NEED HELP: 1974 1.8L Will Only Start with Brake Clean, Runs with AFM disconnected only Options

[Nor.Cal.914]

Hello everyone,

I have a 1974 1.8L that needs a new fuel pump and the customer purchased this pump from Pelican:

https://www.pelicanparts.com/More_Info/0439...59&DID=4630

I have already figured out the line routing in terms of inlet and outlet, but I do have a few questions about some other aspects. Being that the stock pump is a 3-port pump, first question is, what was the reasoning behind the 3 ports instead of just an inlet and outlet? My first thought was maybe an internal FPR, but I see there is a one in the engine compartment so that doesn't seem to be the case, but please correct me if I'm wrong! Second question involves mounting the pump. I have a 1975 so I'm not as familiar with how the 1974's were setup. This car has the coil style ring bracket around the pump which I'm now trying to figure out if I can utilize to mount the new pump. Main issue of course is the fact that all 3 lines came out on one side of the factory pump, whereas this pump has inlet/outlet on either side.

So my question is, what have you guys done to mount your pumps either in the same location or where did you place it instead of the factory location? Thank you in advance for the help! (IMG:style_emoticons/default/beerchug.gif)

-Christopher

[Geezer914]

Get a Delphi pump from Rock Auto for $108!

[Nor.Cal.914]

Get a Delphi pump from Rock Auto for $108!

This was the customer's choice for pump, but yes, I would've gone for a cheaper option myself! (IMG:style_emoticons/default/biggrin.gif)

[Artfrombama]

Get a Delphi pump from Rock Auto for $108!

(IMG:style_emoticons/default/agree.gif) Works for me, mine came from Amazon.

[wonkipop]

have rebuilt two of the old bosch 3 port pumps.
link to the topic with plenty of pics.
go to page 2. some cross sections through the 3 port assembly.

http://www.914world.com/bbs2/index.php?showtopic=350416

its really a kind of staged port assembly with a spring loaded valve.
i think part of what it does is not only relieve pressure if it builds too high for some reason - but also i think it helps dampen pulses from the rotary cell pump.
also remember in these old cars the entire injector circuit was pressurized but using flexible cloth reinforced hoses. so i think the idea was to pressure relieve as a fall back under the threshold where the hoses would fail. which would be catastrophic - you know another thing 914s were famous for. burning.

ultimately the fuel pressure regulator does most of the work relieving pressure and sends fuel back down to the tank via the return line. after the fpr its all just flow not pressure.
but if for any reason the fpr fails or the injector circuit blocks and can''t relieve the whole thing blows out the third port (which is called a return port but really its a relief port) and returns to the tank via the t with the return line coming from the fpr.

the third port blows at about 60-70 psi.
thats how you test them. in a bench test. you should be able to get the pump to build about 60 psi min before it relieves.

but in reality i think not only is fuel being delivered to the injector supply line and the pump building pressure in it, it also always dribbles a bit back through the third port.
esp as the pump ages.

i'm not entire sure why bosch went for these three ports.
i do know that there are some similar bosch pumps that are even slightly earlier that are fitted to mercedes that in fact have the pressure relief inside the pump at the supply (from tank) port and these blow back through the supply line. and are two port while still being roller cell pumps.

but as far as i know all the cars (different makes and models) that ran D jet and early L jet ran these 3 port pumps. not exactly sure what the mercedes two port pumps ran in.
carb? i don't think it was D jet in the case of the pump i was looking at.

however when the 914 went to a front fuel pump in 75 it ran the two port pump or so i think, never having actually seen an original one of those pumps.

i've rebuilt my original 74 1.8 pump and also a virtually identical one from a 74 SAAB that i have as a spare.

----
they evolved quite a bit during the years they were used for D jet applcations.
most of the evolution is on the interior. for instance the early ones have turbulence shrouds inside. later they don't. found to be unnecessary. typical initial german "over engineering". also they gradually shrunk them down in size.

[wonkipop]

and yes you will have a bit of trouble mounting a modern turbine pump in the stock location under the right hand side of the engine bay in a 74. most of the pumps are a bit too long in length.

the issue will be the loop the supply fuel line has to make to get into the top of the pump.
if you can even get a satisfactory slow curve. which i doubt. and if you did it would likely give you trouble with collapsing. producing symptoms like the dread vapor lock problem of legend. but slightly different of course.

i had a turbine 2 port pump mounted in mine while i was rebuilding. i mounted it on the rear wall of the engine side of the passenger compartment. fire wall. this i believe was an earlier location for 3 port pumps in the first few model years. that let me get the lines in and out without any tight curves. later when i reinstalled my rebuilt 3 port i could put it all back in using the original mounting location.

can i suggest if you use a modern rotary fuel pump that you include a high pressure fuel filter in the line after the pump. you can usually mount in the engine bay in line before it gets to the injectors. the original roller cell pumps are real tough dependable units and unlikely to blow themselves apart internally. but modern fuel pumps are another matter.
the last thing you want is pump implosion debris getting to the fuel injectors these days, given they are getting a bit hard to get hold of in some cases.

[wonkipop]

postscript.

went back and re-read my own thread that i posted link to.
its been a while since i rebuilt those pumps.

i thought there was something else the third port does.
it helps with expelling any air in the system and the pump.
if you go to the link i posted above and second page right at the end are some diagrams and a cross section through the pump. the little cylindrical spring loaded valve in the port has a spiral groove in it that lets air bubbles escape down the return port and into the t with the fuel return line from the fpr to the tank.

i guess air bubbles can form in fuel as it cools following shut down. inside the pump and the supply line. so these can escape that way rather than go into the pressurized injector supply line via the delivery port. no doubt helps with cavitation etc. the correct place to put this in the case of EFI cars was in the pump head after pressurization which is really after the fuel supply port. as the body of the fuel pump and supply pprt even though they are full of fuel is not pressurized in one of these roller cell pumps. or it is at least not as pressurized as much as it is right at the delivery port.

whereas in a turbine pump really the whole interior of the pump is pressurized i believe.
so you can do the relief thing and possibly even air bubble relief thing back through the tank supply port.

[Nor.Cal.914]

have rebuilt two of the old bosch 3 port pumps.
link to the topic with plenty of pics.
go to page 2. some cross sections through the 3 port assembly.

http://www.914world.com/bbs2/index.php?showtopic=350416

its really a kind of staged port assembly with a spring loaded valve.
i think part of what it does is not only relieve pressure if it builds too high for some reason - but also i think it helps dampen pulses from the rotary cell pump.
also remember in these old cars the entire injector circuit was pressurized but using flexible cloth reinforced hoses. so i think the idea was to pressure relieve as a fall back under the threshold where the hoses would fail. which would be catastrophic - you know another thing 914s were famous for. burning.

ultimately the fuel pressure regulator does most of the work relieving pressure and sends fuel back down to the tank via the return line. after the fpr its all just flow not pressure.
but if for any reason the fpr fails or the injector circuit blocks and can''t relieve the whole thing blows out the third port (which is called a return port but really its a relief port) and returns to the tank via the t with the return line coming from the fpr.

the third port blows at about 60-70 psi.
thats how you test them. in a bench test. you should be able to get the pump to build about 60 psi min before it relieves.

but in reality i think not only is fuel being delivered to the injector supply line and the pump building pressure in it, it also always dribbles a bit back through the third port.
esp as the pump ages.

i'm not entire sure why bosch went for these three ports.
i do know that there are some similar bosch pumps that are even slightly earlier that are fitted to mercedes that in fact have the pressure relief inside the pump at the supply (from tank) port and these blow back through the supply line. and are two port while still being roller cell pumps.

but as far as i know all the cars (different makes and models) that ran D jet and early L jet ran these 3 port pumps. not exactly sure what the mercedes two port pumps ran in.
carb? i don't think it was D jet in the case of the pump i was looking at.

however when the 914 went to a front fuel pump in 75 it ran the two port pump or so i think, never having actually seen an original one of those pumps.

i've rebuilt my original 74 1.8 pump and also a virtually identical one from a 74 SAAB that i have as a spare.

----
they evolved quite a bit during the years they were used for D jet applcations.
most of the evolution is on the interior. for instance the early ones have turbulence shrouds inside. later they don't. found to be unnecessary. typical initial german "over engineering". also they gradually shrunk them down in size.

Thank you so much for all of the information! It was really interesting to read through it all and through the thread you referenced! I might hang onto this pump to take it apart later and learn from it!


UPDATE:

I was able to install the new fuel pump and get rid of all of my leaks that arose after the pump replacement, but now I'm having starting issues. The engine will only run with the AFM disconnected and will only start after spraying brake clean into the intake. Engine will stay running (poorly - idle speed about 1,200 RPM and feels rough) until you shut it off, but definitely doesn't like to rev up and feels like it's bogging down pretty heavily. I'm not very well versed on this system (L-Jet?), but I've been trying to do some reading in order to figure out where to go next. If the AFM is bad, will it prevent the engine from starting up on its own? What can I do to test it to see if it is actually bad or not? Any advice will be greatly appreciated! Thank you so much!

-Christopher

[dr914@autoatlanta.com]

we sell the conversion kit for 125.00 that includes the pump lines and filter, so the installation is an easy one, if you need good tech advice, just call and we can discuss

Hello everyone,

I have a 1974 1.8L that needs a new fuel pump and the customer purchased this pump from Pelican:

https://www.pelicanparts.com/More_Info/0439...59&DID=4630

I have already figured out the line routing in terms of inlet and outlet, but I do have a few questions about some other aspects. Being that the stock pump is a 3-port pump, first question is, what was the reasoning behind the 3 ports instead of just an inlet and outlet? My first thought was maybe an internal FPR, but I see there is a one in the engine compartment so that doesn't seem to be the case, but please correct me if I'm wrong! Second question involves mounting the pump. I have a 1975 so I'm not as familiar with how the 1974's were setup. This car has the coil style ring bracket around the pump which I'm now trying to figure out if I can utilize to mount the new pump. Main issue of course is the fact that all 3 lines came out on one side of the factory pump, whereas this pump has inlet/outlet on either side.

So my question is, what have you guys done to mount your pumps either in the same location or where did you place it instead of the factory location? Thank you in advance for the help! (IMG:style_emoticons/default/beerchug.gif)

-Christopher

[Nor.Cal.914]

we sell the conversion kit for 125.00 that includes the pump lines and filter, so the installation is an easy one, if you need good tech advice, just call and we can discuss

Thank you very much! I have the new pump installed already and it's working, but now I am trying to tackle the no-start condition.

[StarBear]

Weird that it runs only with the AFM disconnected. Usually it will run for 3-5 seconds before the ECU recognizes that there’s no signal. Try diagnosing with AFM connected to get truer feel for what’s going on.

[Nor.Cal.914]

Weird that it runs only with the AFM disconnected. Usually it will run for 3-5 seconds before the ECU recognizes that there’s no signal. Try diagnosing with AFM connected to get truer feel for what’s going on.

I was able to get it to start on its own with the AFM disconnected one time, but otherwise it will not run with it connected. I tried driving it a short distance with the AFM disconnected and as long as there was minimal throttle input it would drive, but the moment there was anything more than about 15% throttle it choked out and died. I don't have access to any wiring diagrams here, looks like a lot of what's out there is missing most of the fuel injection aspect.

[Artfrombama]

Forgive me if you have already done this but have you checked the fuel pressure? Should be 32-35PSI at idle and should increase slightly as RPM's increase.
Confirm none of the hoses are kinked underneath the tank

Good luck, keep us posted

[Nor.Cal.914]

Forgive me if you have already done this but have you checked the fuel pressure? Should be 32-35PSI at idle and should increase slightly as RPM's increase.
Confirm none of the hoses are kinked underneath the tank

Good luck, keep us posted

Thank you! I haven't checked actual pressure, but I can hook up a gauge to see what it's reading. I might not be working on it again for a few days, but I will update as I can!

[wonkipop]

here is what i think.

a few us here with 1.8s have established that an L jet with its fuel pump wired as per factory original set up will not run with the AFM disconnected.

reason. fuel pump is activated when the ignition is cranked to start - note cranked not just ignition to on. after the engine fires the AFM takes over. the flap will be moved very slightly and activate the fuel pump contact in the AFM unit. the dual relay fitted to the battery tray support on the rhs of the engine bay is part of the equation.
those with heads around electrical can tell you the why and the how.
but thats how it works stock.

hence fuel pump will not run in a stock wired fuel pump set up unless the AFM activates it after the cranking phase. if AFM is disconnected with its plug out it cannot run the fuel pump.

usually the engine will fire initially then pretty much immediately die within seconds if the AFM plug is out. this is how mine behaves. i still have factory stock set up of fuel pump operation.

the whole idea of the L jet fuel pump set up is safety. ie in a crash. engine usually dies/
fuel pump switches off. lowers risk of a dangerous fire with trapped occupants.

-----

now many L jets over the years have had the fuel pump either moved (to front trunk location) or replaced in stock location and have been wired to run when the ignition is in on position. no matter what. hence will always supply fuel regardless of AFM being connected or not connected.

in this sceanario, with the AFM unplugged the car will start and it will idle.
usually slightly elevated. say at 1200-1400 seems to be the usual experience.
if left alone the idle will continue to elevate slowly. it will rise and rise.
gettng to somewhere in the 2000-3000 range. after a few minutes it will die on its own.
but it will run. and you can probably keep it running the way you have with extremely tender throttle inputs. but basically it will not run in any thing you could describe as a satisfactory way.

what you are describing seems to fit this scenario.

ie your fuel pump has been wired to run all the time.
and hence will run without AFM connected. sort of run that is.


---------

so the real problem is with the AFM connected it does not what to fire.
doesn't even want to catch on cranking and at least initially fire let alone continue to run.
i am not sure what exactly that might be causing that.
i have a couple of L jet trouble shooting manuals and can look them up.
see what i can find.

in the meantime some other L jet owner might be able to input here with their suggestions.

if you post a couple of photos of the engine bay that might help.
try and cover all the top of the engine so we can see if anything is obviously missing or disconnected.

--------

in summary what i am saying is i think that it starts on fluild and runs with the AFM disconnected is what we in australia call a "furphy".
you can look that up on google.
don't be distracted by it. its meaningless that it runs in that way.
although it does prove its got spark.
and its got fuel. so its not that.
and maybe not ECU.

your problem is with the AFM connected it does not want to start at all.
this is the REAL problem.
so its AFM?
CHT (cylinder head temp sensor)?
or maybe the dual relay?
or the EFI wiring?
as with all things EFI it will be a matter of methodically testing and checking each component and the wiring.

its also possible your cold start injector is not working.
usually they will fire off that and run briefly off the fuel it provides at cold start.
but you are starting off brake fluid or other starter fluid. so......

i doubt its any kind of vacuum leak, since it will run with the AFM disconnected.
usually an L jet will not run at all with a vacuum leak.

[Nor.Cal.914]

here is what i think.

a few us here with 1.8s have established that an L jet with its fuel pump wired as per factory original set up will not run with the AFM disconnected.

reason. fuel pump is activated when the ignition is cranked to start - note cranked not just ignition to on. after the engine fires the AFM takes over. the flap will be moved very slightly and activate the fuel pump contact in the AFM unit. the dual relay fitted to the battery tray support on the rhs of the engine bay is part of the equation.
those with heads around electrical can tell you the why and the how.
but thats how it works stock.

hence fuel pump will not run in a stock wired fuel pump set up unless the AFM activates it after the cranking phase. if AFM is disconnected with its plug out it cannot run the fuel pump.

usually the engine will fire initially then pretty much immediately die within seconds if the AFM plug is out. this is how mine behaves. i still have factory stock set up of fuel pump operation.

the whole idea of the L jet fuel pump set up is safety. ie in a crash. engine usually dies/
fuel pump switches off. lowers risk of a dangerous fire with trapped occupants.

-----

now many L jets over the years have had the fuel pump either moved (to front trunk location) or replaced in stock location and have been wired to run when the ignition is in on position. no matter what. hence will always supply fuel regardless of AFM being connected or not connected.

in this sceanario, with the AFM unplugged the car will start and it will idle.
usually slightly elevated. say at 1200-1400 seems to be the usual experience.
if left alone the idle will continue to elevate slowly. it will rise and rise.
gettng to somewhere in the 2000-3000 range. after a few minutes it will die on its own.
but it will run. and you can probably keep it running the way you have with extremely tender throttle inputs. but basically it will not run in any thing you could describe as a satisfactory way.

what you are describing seems to fit this scenario.

ie your fuel pump has been wired to run all the time.
and hence will run without AFM connected. sort of run that is.


---------

so the real problem is with the AFM connected it does not what to fire.
doesn't even want to catch on cranking and at least initially fire let alone continue to run.
i am not sure what exactly that might be causing that.
i have a couple of L jet trouble shooting manuals and can look them up.
see what i can find.

in the meantime some other L jet owner might be able to input here with their suggestions.

if you post a couple of photos of the engine bay that might help.
try and cover all the top of the engine so we can see if anything is obviously missing or disconnected.

--------

in summary what i am saying is i think that it starts on fluild and runs with the AFM disconnected is what we in australia call a "furphy".
you can look that up on google.
don't be distracted by it. its meaningless that it runs in that way.
although it does prove its got spark.
and its got fuel. so its not that.
and maybe not ECU.

your problem is with the AFM connected it does not want to start at all.
this is the REAL problem.
so its AFM?
CHT (cylinder head temp sensor)?
or maybe the dual relay?
or the EFI wiring?
as with all things EFI it will be a matter of methodically testing and checking each component and the wiring.

its also possible your cold start injector is not working.
usually they will fire off that and run briefly off the fuel it provides at cold start.
but you are starting off brake fluid or other starter fluid. so......

i doubt its any kind of vacuum leak, since it will run with the AFM disconnected.
usually an L jet will not run at all with a vacuum leak.

wonkipop,

Thank you so much for all of the information! You've been very helpful already! I finally got back onto this car and put a fuel gauge in line to see what I'm working with. I found that with KOEO, there is no pressure, but will build to about 68 PSI when cranking, which seems like it is still wired properly in terms of not running all the time. The engine sputters occasionally with the AFM disconnected, but still won't start on its own and doesn't even attempt to sputter with the AFM connected. By any chance, were you able to locate the L jet troubleshooting manuals? I'm not exactly sure where to go next at the moment. If the dual relay was bad, would it still build fuel pressure when cranking? I wish I knew more in terms of how to test these systems, but any sort of guidance, flow chart, or wiring diagram would be incredibly helpful! I will have to look at my manual when I get home tonight as well to see if there's something in there that I can use. Thank you all for your input so far, I greatly appreciate it!

-Christopher

[Nor.Cal.914]

Here are some pictures of the engine bay. If there's anything I need to take in more detail, please let me know. Thank you!

[Nor.Cal.914]

Last one:

[wonkipop]

@Nor.Cal.914

this link will get you started.
you can download the factory workshop manuals for the 914.
you only need group 2 four cylinder fuel injection volume.

http://p914-6info.net/Manuals.htm

it can be a bit confusing as all the D jet stuff is mixed in there.
the way these factory manuals worked i gather is they issued them at the introduction of the car and then as the model years progressed added sections in.
so the L jet stuff is scattered through out though it is mostly concentrated at the end.

there are some test procedures for each component in the L jet EFI.

but not everything is there.
i have some other stuff which is VW L jet troubleshooting guides which apply to the type 4 VWs. pretty close to the same system as in 914.
and i think somewhere else diagrams for testing the dual relays and ECU harness and plugs etc. but i have to dig them up.
will post later.

[fiacra]

A few thoughts that came to mind when reading your posts. Hopefully these will be helpful....

Here's a thread from another L-Jet owner with a similar problem. One problem was a loose connection at the AFM that wasn't evident until he "wiggled" the wire. The other problem (not in the thread but known from private communication) was that there were multiple vacuum leaks.

http://www.914world.com/bbs2/index.php?sho...342895&st=0

Here's a link to the "914 Tech Notebook" section on Jeff Bowlsby's website. There are multiple L-Jet manuals in this section. Just scroll down through the list and you'll see them, with clickable links. Jeff's website is worth exploring whenever you have the time. Lot's of links to resources there.

https://bowlsby.net/914/Classic/TechNotebook.htm

I had a several week education in L-Let when I revived a 1979 VW Super Beetle from a 16 year nap. By far the best explanation of the system that helped me was in the Bentley manual. There is a section at the rear of the manual dedicated to explaining the system. It was clear and concise, but also probably duplicative of the resources on Jeff's website. PM me with an email and I can probably scan that section for you and email it to you. I might be local to you, depending upon where you are in NorCal, so I could just lend you the manual. I'm in the East Bay. Also, sounds like you have eliminated the dual relay as an issue, but if you are local and are still concerned I do have a known good dual relay you can plug in to confirm.