Is this the dreaded 914 vapor lock?, Asking for your ideas and thoughts Options

[Superhawk996]

This is a head scratcher for sure!

I was reading on the bird forum about a seat belt interlock under the passenger seat that was designed to keep the car from running if the belts aren’t buckled. I do remember trying to start the car right after I bought it, a buzzing sound from that area.

Seat belt interlock / yellow wire bypass will be related to no crank condition, not a no run condition

[Shivers]

I had a leak develop under the fuel tank. Pulled the tank, changed the lines and put it back in. I took it for a drive and it was fine until it died. I stayed near home so I pushed it back and pulled the tank again. When it got warm the fuel line kinked and cut off the fuel. You waited for 3 hours for AAA, I don't think I've ever had vapor lock last that long after the car was off

[ClayPerrine]

This is a head scratcher for sure!

I was reading on the bird forum about a seat belt interlock under the passenger seat that was designed to keep the car from running if the belts aren’t buckled. I do remember trying to start the car right after I bought it, a buzzing sound from that area.
Would the starter work if this relay were malfunctioning?

The relay under the passenger seat blocked the starter from engaging if the seats were occupied and the seat belts were not buckled. If it has not already been bypassed, I suggest you do it. Connect the Yellow and yellow with red heavy wires. I would also suggest that you find the black with a blue tracer wire on the back of the fuse box, fuse 8 that goes to the relay under the passenger seat. It can come out of the relay plug and ground out on the floor. That wire comes from the unfused side of the fuse box, and it is the circuit that powers the coil.

[Chris914n6]

The 3-port recirculates fuel around the engine, instead of putting it back into the tank. So yes, vapor lock happens, because the fuel gets too hot.

You need to wrap the pump so it doesn't get hot air blown on it, from the heat exchanger/heater outlet and the engine cooling air.
It wouldn't hurt to insulate the fuel lines that cross over the engine.

chris, thats not entirely true as i understand them to work.

Your understanding of fluid pumps is off. Too much typing to explain why.

OP issue could be something other than vapor lock. But it is possible that the volume of fuel consumed at speed (adding cool tank gas) exceeded the threshold for vapor lock but at idle conditions were ideal.

A pressure gauge would answer some questions the next time it happens.

[Superhawk996]

On the 3 port pump the port labeled R isn’t flowing any major flow unless the pressure port (D) gets blocked. This R port is controlled by its own mini regulator that is on the pump. In hooking the system up with clear tube there can be a tiny flow OUT of the R port at normal operating pressure.

There is a continual flow back to the tank via tank return line.

[Superhawk996]

Here is the cutaway of the 3 ports as well as the relief valve on the pump that Wonki has previously posted and I’ve personally verified during a 3 port tear down / rebuild.



http://www.914world.com/bbs2/index.php?sho...350416&st=0

Bottom line: the port labeled R ought to be thought of as a pressure RELIEF port. R doesn’t indicate a return path within the pump.

[Artfrombama]

Checked fuel pressure
23 psi regulated, regulator plugged 43psi

I assume the pump and regulator operating normally

[wonkipop]

The 3-port recirculates fuel around the engine, instead of putting it back into the tank. So yes, vapor lock happens, because the fuel gets too hot.

You need to wrap the pump so it doesn't get hot air blown on it, from the heat exchanger/heater outlet and the engine cooling air.
It wouldn't hurt to insulate the fuel lines that cross over the engine.

chris, thats not entirely true as i understand them to work.

Your understanding of fluid pumps is off. Too much typing to explain why.

OP issue could be something other than vapor lock. But it is possible that the volume of fuel consumed at speed (adding cool tank gas) exceeded the threshold for vapor lock but at idle conditions were ideal.

A pressure gauge would answer some questions the next time it happens.

have a look at superhawkes diagram above.

that third port on the fuel pump is not a line where fuel comes back into the pump.
its a port where fuel escapes the pump if excessive pressure builds in the injector supply line out of the pump. that can happen if your fuel pressure regulator sticks shut and does not release pressure and fuel flow out at the design pressure. which in the case of an L jet is 35psi (+/-).

how do i know. i have fully pulled 3 of those pumps apart and rebuilt them.
if you want tech info on the pump to see how the head works with the three ports its in the topic i linked to. port 3 or R is a spring loaded sliding pin that gets pushed by fuel pressure out. it blows open at around 60-70psi. its flow is in one direction. out.

remember the fuel returning from the injector circuit after the fprv is not under pressure. its under pressure before the fprv not after. it flows back to the fuel tank. it physically cannot force its way through that third port on the pump. on the other side of the port inside the pump the fuel is at pressure. 35psi. fuel in the return line to tank is not under pressure. its flowing. the laws of physics prevent it from making its way back into the fuel pump. there is not circuit there. the circuit is the bigger one back through tank.

any fuel in the injector line after the pump and before the fprv should remain under pressure after hot shut down in an engine with a properly function fprv and a fuel pump in good condition. in fact for up to 24 hrs. i've tested mine. same car as one being discussed here. if that line is losing pressure straight away its time to lose the fuel pump. so the injector line does not boil or vaporise fuel after hot shutdown. pressurized fuel is immune to the problem. its the unpressurized fuel before the fuel pump that is a problem in vapor lock conditions.

i am with superhawke on this one.
i doubt this is a vapor lock problem.

the car cut out on the exit ramp off the freeway.
i've never had vapor lock do that. only happens after you shut down and walk away from the car for a time. and i;ve never had it last 3 hours.
so i think its something else.

travelling at freeway speed, even on a hot day, that hot air being released from heater exchanger valve is being instantly sucked out by wind passing under the car. esp if it has the little flaps on the undeside of the body still there. so its not suffering heat problems while the car is moving. esp at higher velocities. maybe stuck it traffic heat can build up there while its running, but not when its moving. no heat comes off the magnesium fan casting while the engine is running. if you don't believe me put your hand on it. it will be stone cold. the heat builds up in the casting after shut down. so there is no heat radiating at the fuel pump etc from it while the car is running at speed.

i've suggested checking the AFM plug and the electrical loom up to it - along with all its connections at the other end. into the ECU and also i think the dual relay.
the symptoms are identical to a AFM plug thats not connecting.
not saying it is that, but its something that ought to be eliminated.

the fact that its staring the next day and running fine from stone cold suggests to me some kind of heat or vibration related issue may the cause. but again not saying it is.

the L jets are a bit different how the fuel pump works.
cranking activates the fuel pump. which pressurizes the circuit.
however as soon as the engine fires there is a hand off to the AFM to run the fuel pump.
the reason this can happen is that the draw from the engine moves the flap and it hits the fuel pump contact switch and takes over running the pump and pressurizing the injector lines. if for any reason that hand off does not happen it won't keep running.

it wil fire off that bit of pressure it gets during cranking, but almost immediately cease running. this does not happen in D jet cars or carb cars. most if not all have the fuel pump running all the time the ignition is on. the L jet car is designed to switch the fuel pump off if the engine stops running. its a safety feature. say in the event of a crash.

sounds like art's car is very original. from what i have seen in photos of it - its vey intact. i'd say all the pump wiring is factory and unmeddled with.

anyone who has owned an L jet knows the embarrassment of not plugging that AFM back in after working on the car and then wondering why it won't run. Starbears done it.
i've done it. interestingly the guys with L jet who have wired in the fuel pump to run all the time get a different phenomina. the engine will start and it will run at elevated idle. the idle just keeps creeping up. and it will run for a while before cutting out. mine is still original. it just fires, runs very briefly and then cuts out.

from what art is describing - its sounds identical.
certainly worth investigating.

[wonkipop]

Checked fuel pressure
23 psi regulated, regulator plugged 43psi

I assume the pump and regulator operating normally

thats a bit out for an L jet.
ones a bit high and ones a bit low.

i'll dig up the proper test from the VW L jet trouble shoot i have.
unplugging the vac hose is involved.
you want to check two values.
i'll post it when it dig it up.

EDIT
here is the test.
from 914 factory manual.
i worked out this is not the full test.
its not testing the drop that should occur at idle or off throttle.
you don't have engine running with this test.




here is the more complete test from a VW Let trouble shoot guide i have.
engine running.



you are after finding those two values.
the higher one quoted in bar is 35psi.
the lower one (at idle) is around 28 psi.

[Artfrombama]

The 3-port recirculates fuel around the engine, instead of putting it back into the tank. So yes, vapor lock happens, because the fuel gets too hot.

You need to wrap the pump so it doesn't get hot air blown on it, from the heat exchanger/heater outlet and the engine cooling air.
It wouldn't hurt to insulate the fuel lines that cross over the engine.

chris, thats not entirely true as i understand them to work.

Your understanding of fluid pumps is off. Too much typing to explain why.

OP issue could be something other than vapor lock. But it is possible that the volume of fuel consumed at speed (adding cool tank gas) exceeded the threshold for vapor lock but at idle conditions were ideal.
I've come to the conclusion that I have an intermittent fuel pressure problem. I checked this morning and the pressures were to spec
A pressure gauge would answer some questions the next time it happens.

have a look at superhawkes diagram above.

that third port on the fuel pump is not a line where fuel comes back into the pump.
its a port where fuel escapes the pump if excessive pressure builds in the injector supply line out of the pump. that can happen if your fuel pressure regulator sticks shut and does not release pressure and fuel flow out at the design pressure. which in the case of an L jet is 35psi (+/-).

how do i know. i have fully pulled 3 of those pumps apart and rebuilt them.
if you want tech info on the pump to see how the head works with the three ports its in the topic i linked to. port 3 or R is a spring loaded sliding pin that gets pushed by fuel pressure out. it blows open at around 60-70psi. its flow is in one direction. out.

remember the fuel returning from the injector circuit after the fprv is not under pressure. its under pressure before the fprv not after. it flows back to the fuel tank. it physically cannot force its way through that third port on the pump. on the other side of the port inside the pump the fuel is at pressure. 35psi. fuel in the return line to tank is not under pressure. its flowing. the laws of physics prevent it from making its way back into the fuel pump. there is not circuit there. the circuit is the bigger one back through tank.

any fuel in the injector line after the pump and before the fprv should remain under pressure after hot shut down in an engine with a properly function fprv and a fuel pump in good condition. in fact for up to 24 hrs. i've tested mine. same car as one being discussed here. if that line is losing pressure straight away its time to lose the fuel pump. so the injector line does not boil or vaporise fuel after hot shutdown. pressurized fuel is immune to the problem. its the unpressurized fuel before the fuel pump that is a problem in vapor lock conditions.

i am with superhawke on this one.
i doubt this is a vapor lock problem.

the car cut out on the exit ramp off the freeway.
i've never had vapor lock do that. only happens after you shut down and walk away from the car for a time. and i;ve never had it last 3 hours.
so i think its something else.

travelling at freeway speed, even on a hot day, that hot air being released from heater exchanger valve is being instantly sucked out by wind passing under the car. esp if it has the little flaps on the undeside of the body still there. so its not suffering heat problems while the car is moving. esp at higher velocities. maybe stuck it traffic heat can build up there while its running, but not when its moving. no heat comes off the magnesium fan casting while the engine is running. if you don't believe me put your hand on it. it will be stone cold. the heat builds up in the casting after shut down. so there is no heat radiating at the fuel pump etc from it while the car is running at speed.

i've suggested checking the AFM plug and the electrical loom up to it - along with all its connections at the other end. into the ECU and also i think the dual relay.
the symptoms are identical to a AFM plug thats not connecting.
not saying it is that, but its something that ought to be eliminated.

the fact that its staring the next day and running fine from stone cold suggests to me some kind of heat or vibration related issue may the cause. but again not saying it is.

the L jets are a bit different how the fuel pump works.
cranking activates the fuel pump. which pressurizes the circuit.
however as soon as the engine fires there is a hand off to the AFM to run the fuel pump.
the reason this can happen is that the draw from the engine moves the flap and it hits the fuel pump contact switch and takes over running the pump and pressurizing the injector lines. if for any reason that hand off does not happen it won't keep running.

it wil fire off that bit of pressure it gets during cranking, but almost immediately cease running. this does not happen in D jet cars or carb cars. most if not all have the fuel pump running all the time the ignition is on. the L jet car is designed to switch the fuel pump off if the engine stops running. its a safety feature. say in the event of a crash.

sounds like art's car is very original. from what i have seen in photos of it - its vey intact. i'd say all the pump wiring is factory and unmeddled with.

anyone who has owned an L jet knows the embarrassment of not plugging that AFM back in after working on the car and then wondering why it won't run. Starbears done it.
i've done it. interestingly the guys who have wired in the fuel pump to run all the time get a different phenomina. the engine will start and it will run at elevated idle. the idle just keeps creeping up. and it will run for a while before cutting out. mine is still original. it just fires, runs very briefly and then cuts out.

from what art is describing - its sounds identical.
certainly worth investigating.

@wonkipop I've come to the conclusion that I have intermittent fuel pressure fluctuations and the rebuilt fuel pump is at fault. Checked pressures earlier and seemed normal (see my previous post) but when I checked again the unregulated pressure was only 14psi.
The reason I don't suspect the AFM is I've been actuating the fuel pump thru the air vane in the AFM.
I've already put in a call to the fuel pump rebuilders and they will test, tear down and repair the pump under warranty. The same company rebuilt the original pump in my 911 and it's been running great since 2018.
This car is sooo much fun, I'm going to miss driving it until repairs have been made.

Thank you, @Chris914n6 @starbear and others for spending the time to help out a 914 noob! (IMG:style_emoticons/default/pray.gif)

[wonkipop]

The 3-port recirculates fuel around the engine, instead of putting it back into the tank. So yes, vapor lock happens, because the fuel gets too hot.

You need to wrap the pump so it doesn't get hot air blown on it, from the heat exchanger/heater outlet and the engine cooling air.
It wouldn't hurt to insulate the fuel lines that cross over the engine.

chris, thats not entirely true as i understand them to work.

Your understanding of fluid pumps is off. Too much typing to explain why.

OP issue could be something other than vapor lock. But it is possible that the volume of fuel consumed at speed (adding cool tank gas) exceeded the threshold for vapor lock but at idle conditions were ideal.
I've come to the conclusion that I have an intermittent fuel pressure problem. I checked this morning and the pressures were to spec
A pressure gauge would answer some questions the next time it happens.

have a look at superhawkes diagram above.

that third port on the fuel pump is not a line where fuel comes back into the pump.
its a port where fuel escapes the pump if excessive pressure builds in the injector supply line out of the pump. that can happen if your fuel pressure regulator sticks shut and does not release pressure and fuel flow out at the design pressure. which in the case of an L jet is 35psi (+/-).

how do i know. i have fully pulled 3 of those pumps apart and rebuilt them.
if you want tech info on the pump to see how the head works with the three ports its in the topic i linked to. port 3 or R is a spring loaded sliding pin that gets pushed by fuel pressure out. it blows open at around 60-70psi. its flow is in one direction. out.

remember the fuel returning from the injector circuit after the fprv is not under pressure. its under pressure before the fprv not after. it flows back to the fuel tank. it physically cannot force its way through that third port on the pump. on the other side of the port inside the pump the fuel is at pressure. 35psi. fuel in the return line to tank is not under pressure. its flowing. the laws of physics prevent it from making its way back into the fuel pump. there is not circuit there. the circuit is the bigger one back through tank.

any fuel in the injector line after the pump and before the fprv should remain under pressure after hot shut down in an engine with a properly function fprv and a fuel pump in good condition. in fact for up to 24 hrs. i've tested mine. same car as one being discussed here. if that line is losing pressure straight away its time to lose the fuel pump. so the injector line does not boil or vaporise fuel after hot shutdown. pressurized fuel is immune to the problem. its the unpressurized fuel before the fuel pump that is a problem in vapor lock conditions.

i am with superhawke on this one.
i doubt this is a vapor lock problem.

the car cut out on the exit ramp off the freeway.
i've never had vapor lock do that. only happens after you shut down and walk away from the car for a time. and i;ve never had it last 3 hours.
so i think its something else.

travelling at freeway speed, even on a hot day, that hot air being released from heater exchanger valve is being instantly sucked out by wind passing under the car. esp if it has the little flaps on the undeside of the body still there. so its not suffering heat problems while the car is moving. esp at higher velocities. maybe stuck it traffic heat can build up there while its running, but not when its moving. no heat comes off the magnesium fan casting while the engine is running. if you don't believe me put your hand on it. it will be stone cold. the heat builds up in the casting after shut down. so there is no heat radiating at the fuel pump etc from it while the car is running at speed.

i've suggested checking the AFM plug and the electrical loom up to it - along with all its connections at the other end. into the ECU and also i think the dual relay.
the symptoms are identical to a AFM plug thats not connecting.
not saying it is that, but its something that ought to be eliminated.

the fact that its staring the next day and running fine from stone cold suggests to me some kind of heat or vibration related issue may the cause. but again not saying it is.

the L jets are a bit different how the fuel pump works.
cranking activates the fuel pump. which pressurizes the circuit.
however as soon as the engine fires there is a hand off to the AFM to run the fuel pump.
the reason this can happen is that the draw from the engine moves the flap and it hits the fuel pump contact switch and takes over running the pump and pressurizing the injector lines. if for any reason that hand off does not happen it won't keep running.

it wil fire off that bit of pressure it gets during cranking, but almost immediately cease running. this does not happen in D jet cars or carb cars. most if not all have the fuel pump running all the time the ignition is on. the L jet car is designed to switch the fuel pump off if the engine stops running. its a safety feature. say in the event of a crash.

sounds like art's car is very original. from what i have seen in photos of it - its vey intact. i'd say all the pump wiring is factory and unmeddled with.

anyone who has owned an L jet knows the embarrassment of not plugging that AFM back in after working on the car and then wondering why it won't run. Starbears done it.
i've done it. interestingly the guys who have wired in the fuel pump to run all the time get a different phenomina. the engine will start and it will run at elevated idle. the idle just keeps creeping up. and it will run for a while before cutting out. mine is still original. it just fires, runs very briefly and then cuts out.

from what art is describing - its sounds identical.
certainly worth investigating.

@wonkipop I've come to the conclusion that I have intermittent fuel pressure fluctuations and the rebuilt fuel pump is at fault. Checked pressures earlier and seemed normal (see my previous post) but when I checked again the unregulated pressure was only 14psi.
The reason I don't suspect the AFM is I've been actuating the fuel pump thru the air vane in the AFM.
I've already put in a call to the fuel pump rebuilders and they will test, tear down and repair the pump under warranty. The same company rebuilt the original pump in my 911 and it's been running great since 2018.
This car is sooo much fun, I'm going to miss driving it until repairs have been made.

Thank you, @Chris914n6 @starbear and others for spending the time to help out a 914 noob! (IMG:style_emoticons/default/pray.gif)

yeah i can see the values. they are a bit out.
highly likely it simply was unable to build sufficient fuel pressure to fire the injectors when you were having that problem.

the AFM problem i was hinting at would have been a bastard to locate.
because i was getting at the idea it was losing a connection due to heat or something like that. it would have been real hard to track down.
sort of thing though that starts to happen with ancient half a century old wiring and components.

re the pump. problem is likely to be in that third port. the one i was explaining the function of to chris914n6. that pin and spring could well be defective and its allowing itself to open far under design pressure. hence pressure leaks out there.
this happens to the pumps over time as they age. if you switch off and the injector loop does not hold fuel pressure it means its instantly leaking out of that port on the pump. there is a little rubber tip on it that seals in the fuel pressure remaining in the injector loop.
obviously if the car runs it is not the fuel pressure regulator. what the pump is having to do is work overtime to hold pressure in the line against the regulator but also against itself because its just flowing out the "emergency back door.."

my memory of taking it all apart is you have to be incredibly careful with the soft aluminium crimped cap that holds all that relief valve spring gear in there. if for any reason the springs can catch on its inside face the whole gizmo just won't work correctly. it can stick.

as i say a good pump and a good fpr should hold pressure in the injector rail for a surprisingly long amount of time. anything up to 24 hrs believe it or not. a good system in an L jet being driven every day will give absolutely instant starting of the engine.
starter motor barely turns.

[wonkipop]

so let me get this right with the test you did.
you unplugged fuel regulator and plugged line and tested and got 43 psi.
that means your pump could only muster 43 psi before it was blowing out the back door.
a good one will get to about 60-70 psi.
thats basically the same test i did on my rebuilt pumps if i understand you right.
we were using a guage that had an adjustable tap on it.
setting it to values of first 28 then 35 simulating the fpr. it was making it.
then we kept cranking it until we got it to shoot out port 3.
happened at 60-70 depending on the pump i was testing.

additional to the ultimate pressure test the whole deal has to be able to do those two values i posted. theoretically with the fuel pressure regulator plugged in and being tested it should still be able to make the pressures of 28 and 35 in the injector line even with weaker value of 43 max made by pump. its a bit of a close margin but its there.
thats if the fpr is good.

unless that 43 is not something its able to make consistently.

i'm reading your second test again carefully.
so you are saying that once again you plugged line before fpr.
ie ultimate test of pump against completely closed line.
and all it could muster was 14psi.
so was blowing out the back door at 14 psi.

if so. pump ratshit. probably in that spring thing.
either backflowing down supply line frpm tank because rubber tip on pin is rooted or not there or not seated properly. or the spring is catching and the whole jigger is jammed open letting it flow out of the final escape port back to the tank.

[bkrantz]

Here is what I would do to diagnose it.

Get a mechanical fuel pressure gauge. Take your engine lid off the car. Hook the pressure gauge up so the hose is long enough that you can use duct tape to tape it to the rear window, where it can be seen from the driver's seat with the rear view mirror. (Fuel in the passenger compartment is not a good idea) Then drive it in the same conditions (as close as you can get) on the same route. If it happens again, check the fuel pressure gauge. If it is vapor locked, you will not have fuel pressure.

I would consider moving the pump up front as they did in the 75 and later cars. It may not be the absolutely concourse stock location, but it would help if it is vapor locking.

If you do that, be VERY, VERY careful about all the connections, including the fluid integrity of the gauge itself. Spraying fuel from a high point over a hot engine could be exciting.

[Artfrombama]

so let me get this right with the test you did.
you unplugged fuel regulator and plugged line and tested and got 43 psi.
that means your pump could only muster 43 psi before it was blowing out the back door.
a good one will get to about 60-70 psi.
thats basically the same test i did on my rebuilt pumps if i understand you right.
we were using a guage that had an adjustable tap on it.
setting it to values of first 28 then 35 simulating the fpr. it was making it.
then we kept cranking it until we got it to shoot out port 3.
happened at 60-70 depending on the pump i was testing.

additional to the ultimate pressure test the whole deal has to be able to do those two values i posted. theoretically with the fuel pressure regulator plugged in and being tested it should still be able to make the pressures of 28 and 35 in the injector line even with weaker value of 43 max made by pump. its a bit of a close margin but its there.
thats if the fpr is good.

unless that 43 is not something its able to make consistently.

i'm reading your second test again carefully.
so you are saying that once again you plugged line before fpr.
ie ultimate test of pump against completely closed line.
and all it could muster was 14psi.
so was blowing out the back door at 14 psi.

if so. pump ratshit. probably in that spring thing.
either backflowing down supply line frpm tank because rubber tip on pin is rooted or not there or not seated properly. or the spring is catching and the whole jigger is jammed open letting it flow out of the final escape port back to the tank.

Yeh Sunday I got in the car, hit the key and immediately fired and idled great. I didn’t drive the car because it had been raining.
Got under the car and checked the fuel hoses from the tank, we’re ok.
Hooked up my pressure gauge to the test nipple and read 23psi, clamped the hose before the PR with hemostats and read dead head pressure, 43psi. Then I checked pressure straight out of the pump 14psi

[wonkipop]

so let me get this right with the test you did.
you unplugged fuel regulator and plugged line and tested and got 43 psi.
that means your pump could only muster 43 psi before it was blowing out the back door.
a good one will get to about 60-70 psi.
thats basically the same test i did on my rebuilt pumps if i understand you right.
we were using a guage that had an adjustable tap on it.
setting it to values of first 28 then 35 simulating the fpr. it was making it.
then we kept cranking it until we got it to shoot out port 3.
happened at 60-70 depending on the pump i was testing.

additional to the ultimate pressure test the whole deal has to be able to do those two values i posted. theoretically with the fuel pressure regulator plugged in and being tested it should still be able to make the pressures of 28 and 35 in the injector line even with weaker value of 43 max made by pump. its a bit of a close margin but its there.
thats if the fpr is good.

unless that 43 is not something its able to make consistently.

i'm reading your second test again carefully.
so you are saying that once again you plugged line before fpr.
ie ultimate test of pump against completely closed line.
and all it could muster was 14psi.
so was blowing out the back door at 14 psi.

if so. pump ratshit. probably in that spring thing.
either backflowing down supply line frpm tank because rubber tip on pin is rooted or not there or not seated properly. or the spring is catching and the whole jigger is jammed open letting it flow out of the final escape port back to the tank.

Yeh Sunday I got in the car, hit the key and immediately fired and idled great. I didn’t drive the car because it had been raining.
Got under the car and checked the fuel hoses from the tank, we’re ok.
Hooked up my pressure gauge to the test nipple and read 23psi, clamped the hose before the PR with hemostats and read dead head pressure, 43psi. Then I checked pressure straight out of the pump 14psi

yeah when its idling the vac line to the fuel pressure regulator reduces pressure to 28psi - all it needs for idle. so the pump is able to just make that pressure. sort of, against the fuel pressure regulator. enough for it to idle anyway. would have been interesting to give it a bit of stick and see what happens. its got to make 35psi in that circumstance.

a bit more stress on it with a hard dead head pressure and its just blowing the relief port open on the pump. it really should be able to climb all the way to somewhere in that vicinity of 60psi before it lets go.

really sounds like the spring bit inside that port is all wrong. that little cap on the pump head that is made of soft aluminium holds it all in. from memory its two springs. one inside the other. its like a two stage thing. one spring keeps it against the injector feed port when the pumps off and closes off the port so the injector line keeps pressure. the fuel pressure regulator keeps it pressured at the other end. normal operation of pump can compress that spring and allows delivery to the injector line.

the other spring comes in to play when the pressures rise in the pump head and it gets forced further out. that spring resists up to about 60 psi and then gets compressed enough to open the third port, the so called return port. sounds like spring is kaput somehow.

when you say you were checking the pressure straight out of pump.
which hose or port where you connecting to.
was that the third port. the so called return port.
straight out of pump it should be able to do the equal of your dead head test.
43 psi. thats at the delivery port.
?

[JamesM]

With a recirculating fuel system...can a 914 **really** get vapor lock?

Dead-end fuel system with carbs, sure. But L- or D-Jet...?

Discuss.

Yes.

If it boils just in the fuel rail lines you can usually clear with with a few key cycles however if it boils in/before the pump with the pump in the engine bay you lose prime on the pump and nothing but time and cooling the pump down will get you going again.


Here is something else to think about, the boiling point of ethanol at sea level is only 173F and it just gets worse as you go up in altitude. Near 10,000 feet its only 155F

Just another reason corn gas absolutely sucks in these cars.

This is something I have witnessed and repeated first hand. There is a drive I like to take out here over Guardsman's pass that hits 10,000 feet and one of my 914s still has the fuel pump in the stock location. Warm summer days in Utah tend to hit over 100F. I always try to run ethanol free gas however there are occasions where ill go on drives, need gas, and there just isnt any around. Now if I have ethanol free gas in the tank I wont have any problems up on the pass, if I however forget that I have filled up with ethanol blend and make the same drive (which I have done on a couple occasions) I am in for a long day.

Made the same mistake at Red Rocks Classic a few years back, took the car with the rear pump out to Colorado. No issues at all on the way out as I know where to get ethanol free on the way. 2nd day of driving in Colorado I had to fill with Ethanol blend, and we were driving Grand Mesa (which i didnt realize was over 11,000 elevation) and I found myself stopped a few times dumping water on my fuel pump to cool things off.

When you have ambient temps near 100, asphalt temps near 150, an engine case running 200+ right next to your fuel pump and a component making up 10% of your fuel that turns to air bubbles at 155, it doesn't take long after the fuel flow stops for there to be problems. Sometimes you even get problems before the flow stops.

Not an issue with the pump under the tank, pump stays cooler, gas before the pump stays much cooler, and you don't have as long a feed line for air bubbles to get trapped in and all the lines that take the engine bay heat are under pressure greatly increasing the boiling temp.

[ClayPerrine]

If it boils just in the fuel rail lines you can usually clear with with a few key cycles however if it boils in/before the pump with the pump in the engine bay you lose prime on the pump and nothing but time and cooling the pump down will get you going again.

Unfortunately this won't work in this case. This is L-Jet. It does not have the 2 second fuel pump prime function that is in D-Jet.

[Artfrombama]

so let me get this right with the test you did.
you unplugged fuel regulator and plugged line and tested and got 43 psi.
that means your pump could only muster 43 psi before it was blowing out the back door.
a good one will get to about 60-70 psi.
thats basically the same test i did on my rebuilt pumps if i understand you right.
we were using a guage that had an adjustable tap on it.
setting it to values of first 28 then 35 simulating the fpr. it was making it.
then we kept cranking it until we got it to shoot out port 3.
happened at 60-70 depending on the pump i was testing.

additional to the ultimate pressure test the whole deal has to be able to do those two values i posted. theoretically with the fuel pressure regulator plugged in and being tested it should still be able to make the pressures of 28 and 35 in the injector line even with weaker value of 43 max made by pump. its a bit of a close margin but its there.
thats if the fpr is good.

unless that 43 is not something its able to make consistently.

i'm reading your second test again carefully.
so you are saying that once again you plugged line before fpr.
ie ultimate test of pump against completely closed line.
and all it could muster was 14psi.
so was blowing out the back door at 14 psi.

if so. pump ratshit. probably in that spring thing.
either backflowing down supply line frpm tank because rubber tip on pin is rooted or not there or not seated properly. or the spring is catching and the whole jigger is jammed open letting it flow out of the final escape port back to the tank.

Yeh Sunday I got in the car, hit the key and immediately fired and idled great. I didn’t drive the car because it had been raining.
Got under the car and checked the fuel hoses from the tank, we’re ok.
Hooked up my pressure gauge to the test nipple and read 23psi, clamped the hose before the PR with hemostats and read dead head pressure, 43psi. Then I checked pressure straight out of the pump 14psi

yeah when its idling the vac line to the fuel pressure regulator reduces pressure to 28psi - all it needs for idle. so the pump is able to just make that pressure. sort of, against the fuel pressure regulator. enough for it to idle anyway. would have been interesting to give it a bit of stick and see what happens. its got to make 35psi in that circumstance.

a bit more stress on it with a hard dead head pressure and its just blowing the relief port open on the pump. it really should be able to climb all the way to somewhere in that vicinity of 60psi before it lets go.

really sounds like the spring bit inside that port is all wrong. that little cap on the pump head that is made of soft aluminium holds it all in. from memory its two springs. one inside the other. its like a two stage thing. one spring keeps it against the injector feed port when the pumps off and closes off the port so the injector line keeps pressure. the fuel pressure regulator keeps it pressured at the other end. normal operation of pump can compress that spring and allows delivery to the injector line.

the other spring comes in to play when the pressures rise in the pump head and it gets forced further out. that spring resists up to about 60 psi and then gets compressed enough to open the third port, the so called return port. sounds like spring is kaput somehow.

when you say you were checking the pressure straight out of pump.
which hose or port where you connecting to.

The middle "D" port

was that the third port. the so called return port.
straight out of pump it should be able to do the equal of your dead head test.
43 psi. thats at the delivery port.
?

I too believe the problem is with the bypass, the pump runs, doesn't leak just no pressure.
Pump is headed back to the rebuilders for round 2. Ordered a Pierburg (sp?) from the jungle site to get the car going for the 3+ weeks it's going to take to get my 0 580 463 009 original back.

[wonkipop]

so let me get this right with the test you did.
you unplugged fuel regulator and plugged line and tested and got 43 psi.
that means your pump could only muster 43 psi before it was blowing out the back door.
a good one will get to about 60-70 psi.
thats basically the same test i did on my rebuilt pumps if i understand you right.
we were using a guage that had an adjustable tap on it.
setting it to values of first 28 then 35 simulating the fpr. it was making it.
then we kept cranking it until we got it to shoot out port 3.
happened at 60-70 depending on the pump i was testing.

additional to the ultimate pressure test the whole deal has to be able to do those two values i posted. theoretically with the fuel pressure regulator plugged in and being tested it should still be able to make the pressures of 28 and 35 in the injector line even with weaker value of 43 max made by pump. its a bit of a close margin but its there.
thats if the fpr is good.

unless that 43 is not something its able to make consistently.

i'm reading your second test again carefully.
so you are saying that once again you plugged line before fpr.
ie ultimate test of pump against completely closed line.
and all it could muster was 14psi.
so was blowing out the back door at 14 psi.

if so. pump ratshit. probably in that spring thing.
either backflowing down supply line frpm tank because rubber tip on pin is rooted or not there or not seated properly. or the spring is catching and the whole jigger is jammed open letting it flow out of the final escape port back to the tank.

Yeh Sunday I got in the car, hit the key and immediately fired and idled great. I didn’t drive the car because it had been raining.
Got under the car and checked the fuel hoses from the tank, we’re ok.
Hooked up my pressure gauge to the test nipple and read 23psi, clamped the hose before the PR with hemostats and read dead head pressure, 43psi. Then I checked pressure straight out of the pump 14psi

yeah when its idling the vac line to the fuel pressure regulator reduces pressure to 28psi - all it needs for idle. so the pump is able to just make that pressure. sort of, against the fuel pressure regulator. enough for it to idle anyway. would have been interesting to give it a bit of stick and see what happens. its got to make 35psi in that circumstance.

a bit more stress on it with a hard dead head pressure and its just blowing the relief port open on the pump. it really should be able to climb all the way to somewhere in that vicinity of 60psi before it lets go.

really sounds like the spring bit inside that port is all wrong. that little cap on the pump head that is made of soft aluminium holds it all in. from memory its two springs. one inside the other. its like a two stage thing. one spring keeps it against the injector feed port when the pumps off and closes off the port so the injector line keeps pressure. the fuel pressure regulator keeps it pressured at the other end. normal operation of pump can compress that spring and allows delivery to the injector line.

the other spring comes in to play when the pressures rise in the pump head and it gets forced further out. that spring resists up to about 60 psi and then gets compressed enough to open the third port, the so called return port. sounds like spring is kaput somehow.

when you say you were checking the pressure straight out of pump.
which hose or port where you connecting to.

The middle "D" port

was that the third port. the so called return port.
straight out of pump it should be able to do the equal of your dead head test.
43 psi. thats at the delivery port.
?

I too believe the problem is with the bypass, the pump runs, doesn't leak just no pressure.
Pump is headed back to the rebuilders for round 2. Ordered a Pierburg (sp?) from the jungle site to get the car going for the 3+ weeks it's going to take to get my 0 580 463 009 original back.

yes
but i was just concerned you were getting only 23/24 psi on the test with the fuel pressure regulator in circuit.

when you get the pump back and hooked up do the full proper test.

you can see how it works from the tech pages i posted.
you can do the upper pressure test either with engine running or not.
you just activate the pump via the flapper as you have been doing without engine running.
when you do that one you have to get 35 psi +/- i psi or so.
its different from d jets and some literature confuses saying 28 psi. its not its 35.

the more full test is to have the engine running and the vac hose in the fpr.
you use the test nipple on the injector ring. at idle it should be 28 psi. or plus or minus 1. the vacuum is activating the fpr to open more than when no vac. then raise the revs up. go to 2000 or more. fuel pressure should rise to 35 psi. drop the revs off, should fall to 28 again. this will ensure your fpr is also behaving. i don't know if you replaced your fpr when you got it back on the road. but make sure its operating correctly too.

they are non serviceable and non adjustable on L jets and different from the fpr on the D jets. if its not working probably you have to find a replacement unit.

all the best with it.
and yes, very fun cars to drive. (IMG:style_emoticons/default/beerchug.gif) (IMG:style_emoticons/default/beerchug.gif)

[Artfrombama]

Discovered the temp sensor in the RH head became disconnected.