‘74 1.8L L-Jetronic Cold Start Low Idle, Mystery solved! Options

[wonkipop]

If you are starting without the pin hooked up you should be running solely on existing fuel pressure as your pump shouldn't work.

I would’ve said the same thing prior to this, but it ran for a good while. At 2k RPM mind you.

@wonkipop
I can attest that when the thermo time switch is above the rated temp, the circuit is open. As for it ever allowing the CSV to run longer than it’s rated 8sec. I doubt it. But, it would be testable.

As for my current status, technically, I haven’t ruled out a temp sensor 1 issue. As the two resistance tests in the manual only say to test between pin 6 & 9, and 7 & 8 with no explanation as to what those readings are confirming. I think I will call fuel injection corp and ask them.

Further, the way the engine ran when the AFM was unplugged had no stumbling or anything like that. It was smooth and consistent. Which means, I need to drop the theory on a mechanical fault.

For now, I just need to think about what just happened and understand if it is an exception or if other 1.8’s do the same.

thats interesting.
because its saying at rated temp, its on for 8 seconds.

and it needs electricity to warm it.
which isn't going to be instantaneous is it?
and that mechanism is internal to it.
its not unlike an AAV?

its like it goes on at 13C, keeps the CSI open and shuts off the CSI as soon as it warms it to the cut off temp. which must be a little bit higher?
and at that little bit higher temp when its warmed by ambient or engine block temp it never switches on because its open.

i always thought the thing about their factory manual test at 50F (or whatever it is exactly) is to time the CSI squirting is just a kind of standard to see it worked and to time it working at that spec temp.

anyway i could have been running off residual fuel pressure today,
or i could have been running off the CSI even though it wasn't below 13C.
or i could have had fuel pressure and injectors firing but set for warm engine with no other information and it just gave up.

i'll give it another shot from cold with the plug out and give it a second turn of the key after it dies. i'll try and listen to the pump as well for you in all the chaos. with the pin out theoretically it will not be running (even if i crank?). anyway i should have bled off all fuel pressure today in the test i did for you van. so tomorrow might be interesting.
that will tell us at least whether it was just residual fuel pressure and we can settle that question mark for you van. (unless for some reason the fuel pump goes when you crank but switches off unless the AFM plug tells it to keep going?).

can't wait for steve's test.

[StarBear]

Still snowy, icy and sleet here today. Possibly tomorrow; maybe Sunday before I can push it out of the garage to test. (IMG:style_emoticons/default/sad.gif)

[Van B]

No worries! I appreciate the assist!

[wonkipop]

ok @Van B

and @djway .

i had to sleep on this fuel pump working thing.

schematically it is true that the stator flap runs the fuel pump once the engine has started. but.
that is when its above idle.
or below full throttle.

the fuel pump will not be run by the AFM until the AFM takes over.
the AFM takes over when the stator flap opens a small set amount and closes the fuel pump contact. this causes the stator flap to take over operating the fuel pump.

that occurs after the throttle is opened - to move the stator flap - and to move the throttle switch off the idle position - which switches off the throttle switch controlling the fuel pump.

the stator flap can only move (once the engine has warmed and the AAV has closed) if the throttle is opened.

its an on off throttle switch in the L jet cars. its only on at idle and at full throttle.
in between the throttle switch shuts off and does not control fuel supply (ie the fuel pump). the stator flap takes over in between. this works in reverse when you deaccelerate and close the throttle. the stator closes and stops supplying the fuel pump with power to operate, and the throttle switch takes over again and supplies signal for idle fuel metering.

i am fairly sure i have this right.
theoretically a 1.8 can run at idle without the stator flap controlling the fuel pump and the fuel pump will run at least.

to me that says it is possible for van's car to run as it did.

you can also look at it from the AFM flap end of things.
if the car is warm and the aav is closed the stator flap should be closed?
the idle air is drawn in via the idle by pass passage without moving the stator flap.
i believe this is the case. the stator flap is not being deflected when the car is at stable warm idle.
if the stator flap does not move the fuel pump contact does not close.
its impossible for the fuel pump to be operated by the AFM at normal warm idle.
its operated by something else at warm idle.
the throttle switch?

they basically pass the batten once you open the throttle.

now as to why vans ran and mine spluttered to a halt.
i'm not sure.

all his components are in fine form.
maybe that was enough to get it to run.

who knows with mine.
things could have deteriorated over the last 2 years since i woke it up.
aav might not be working so well again.
cht might have gone down hill since bringing it back to life.
i haven't tuned it for 12 months but its still running just fine.

i could do a second test on mine i think which may be more informative.
which is to warm it fully up.
take the cold start out of the equation.
and see if it will start itself and continue to run at idle with the AFM pin pulled out.


---

this is all tied in with the so called safety circuit.
which is designed to stop the fuel pump after an accident if the ignition is still on.
i'm still trying to get my head around that.
somehow once the engine stops it must all switch off even if the ignition is on.
but i don't really understand that bit yet.

but the fuel pump works
1) when the engine is cranked. pressurises the sytem.
which may still have some residual pressure in it that it can hold for some time depending on the state of the regulator, the fuel pump back flow valve etc.
2) when the AFM tells it to work as it opens.
3) by something else when its at idle because it ain't the AFM.

[wonkipop]

test 2 for you @Van B

light pictorial relief of lab conditions.
late summer.
28.5 C
slob australian youth glued to hi phone providing background context so you know its not faked from a location in the northern hemisphere.



warmed it up fully.

now i know my fuel system retains pressure beautifully.
i rarely start it 2 days in a row.
didn't even crank. exploded into life at turn of the key.

pulled switch.

cranked.
ran for i estimate 3 seconds.

cranked again.
struggled and tried to run and got to about 5 seconds maybe 6.

cranked third time.
repeat of 1.

cranked fourth time.
repeat of 1.

mine will not run with the plug out. even warmed.

conclude yesterday it did indeed run off the squirt from the cold start injector for the 10 seconds it went.

could not hear fuel pump during test crank and brief run.
doesn't mean it wasn't running. just could not detect it from where i stood cranking.

mysteries of 914.
might read up again on just how that pump is running in the idle mode.

[Van B]

Thanks @wonkipop love the pic too! Kinda captured an impressionist moment there.

Anyway, your test is what I would’ve expected. I appreciate you doing that. We’ll see what @StarBear gets. This isn’t just a fuel pump running, but also injectors are firing in time…. I just can’t understand this car!

[wonkipop]

was interested myself in how the fuel pump runs at idle.
would have been nice to have detected it going if it was.
impossible to get my stoopid head under car without ramps or something.

interesting that it did fire.
injectors must have fired? even briefly/weakly.
wouldn't have been anything else. was well and truly warmed up.

least i know my csi works.
what made it run for sure yesterday.
it ran strongly at 850 for those 10 seconds.

today it was a barely go situation for the 5 seconds max it tried to run.

[djway]

AFM needed to close the circuit.
You probably ran on stored pressure without any pump.

[wonkipop]

AFM needed to close the circuit.
You probably ran on stored pressure without any pump.

which means the stator flap is moved at idle.
maybe not opened to air flow but sucked by engine vacuum a small amount - enough to close the contact and run the fuel pump?

which means that van's fuel pump has been wired to run un-commanded by the stator flap. only way his could have run?

[Van B]

AFM needed to close the circuit.
You probably ran on stored pressure without any pump.

which means the stator flap is moved at idle.
maybe not opened to air flow but sucked by engine vacuum a small amount - enough to close the contact and run the fuel pump?

which means that van's fuel pump has been wired to run un-commanded by the stator flap. only way his could have run?

That is another thing to check for sure. But It’s a secondary target. The question I want to answer is not how did it run? Rather, I want to to know why it ran the way that it did?

Since the fuel pump runs with or without the AFM plugged in, then it cancels out of the equation.

[wonkipop]

AFM needed to close the circuit.
You probably ran on stored pressure without any pump.

which means the stator flap is moved at idle.
maybe not opened to air flow but sucked by engine vacuum a small amount - enough to close the contact and run the fuel pump?

which means that van's fuel pump has been wired to run un-commanded by the stator flap. only way his could have run?

That is another thing to check for sure. But It’s a secondary target. The question I want to answer is not how did it run? Rather, I want to to know why it ran the way that it did?

Since the fuel pump runs with or without the AFM plugged in, then it cancels out of the equation.

true.

i think its a separate problem from the warm up problem, which remains similar in profile to mine.

yours ran without the afm connected because -
it ran off the throttle switch in the idle position.
the only way it could have? and it got fuel.

i got my head around the AFM.
its not an arc inside like i pictured it.
more like a rotary engine combustion chamber.
at idle the engine vacuum is enough to pull the stator flap in the first pure arc to operate the fuel pump but not admit additional combustion air.
the warm idle fuel amount is controlled by the throttle switch, not the AFM in that region?
thats what i can work out.

though there is a little bit of conflicting information on that in the manual that implies the idle position on the throttle switch is not used. but elsewhere it says it is.
having to read and re read this stuff.

the aav happily sucked the stator flap well open to let the additional air in without the computer knowing about it?
it kind of went half mechanical in a way?
mixing that air that it didn't know was coming in with the fuel it was happily supplying.

the errant fuel pump let it do it?

so, it doesn't really get us any closer to whats the warm up hole our engines fall into.

-------

emery can likely explain why it ran the way it did precisely.
but factors could be something like this.
cht told the computer it was stone cold? so whatever idle switch normally wanted for fuel it got more because it was stone cold?
aav closing slowly changes amount of air but let a lot in to start.
engine warms up a bit as it proceeds changing combustion chamber conditions.
fuel condensation etc.
engine speed rises on its own because aav is acting like a kind of throttle in relation to rising engine temp. and it kind of does a little runaway?......for a while.

and ------ whatever fuel it got from the throttle switch position with an input from the cht was more than it would have got from the aav sucking the stator flap open and the afm controlling the warm up when its plugged in? why it started at 1400. that amount of fuel and that amount of air let it run at 1400 from cold. and for a while the two graphs of diminishing air and rising temp kept the fuel mix in the zone for it to sit at 1400 rpm.

i can't think of anything else that would explain it.

[StarBear]

Ok folks, here are my results. Day at about 35F:
Test 1- sitting for 2-3 weeks, started on sixth crank with no throttle. Ran about 10 secs at wavering idle of 850-1000 rpm. Died.
Test 2- Waited 30 secs. Started on second crank and ran for 30 secs first at 850-1000 rpm then crept up to 1500 rpm before died.
Test 3- Waited 30 secs. Started on second crank and ran for 40 secs first at 1000 rpm then crept up to 1800-2000 rpm then died.
Weird behavior, eh? Neither of ours show the same action. Somewhat similar but not the same. (IMG:style_emoticons/default/confused24.gif) Temp? Barometer? Magic? (IMG:style_emoticons/default/w00t.gif)
At least they start and winter hasn’t killed the battery so getting ready for actual driving! (IMG:style_emoticons/default/driving.gif)

[Van B]

@StarBear @wonkipop
This is very informative! So, setting aside the likely theory that when my fuel pump was moved it was wired to pull from a different 12v source, your test confirms that they will start and go to an abnormally high idle without the AFM. And, importantly, yours ran longer and at a faster rpm than the cold start injector could support meaning the injectors are functional without the AFM.

Today has been another day of mystery for me. My timing was still a little off from my previous experiments, but when I cold started the car today, other than needing 4-5 revolutions before firing, it had proper cold start behavior!

Before I attempted the start, I took the points out and discovered that the washer on the screw was split in two pieces (IMG:style_emoticons/default/confused24.gif) and that the points action was a little sticky. So I replaced the washer, sanded the points lightly to make them a little more parallel, ran a bunch of WD-40 through the lever arm, and then re-gapped them to .38mm.

After a few cranks, the car started, went to 1400RPM just like it did without the AFM, but didn’t climb higher this time. After a couple minutes, it fell to around 1000RPM and stayed there. I let it keep running until fully warm and found that the timing and air screw both needed to be adjusted.

I went for a short drive (rolled 53k miles btw) and the car definitely likes .38mm vs the .4mm I had previously. But I was also wondering how that broken washer may have been effecting the points? I started to think it had allowed the points to move or something.

I’m also wondering if starting without the AFM had reset something in the computer? What I need now is repeatability. So, I’ll let the car get cold again and hopefully get another chance for a cold start and another in the morning.

I suppose I can investigate the fuel pump 12v wire in the meantime…

Thanks guys!

Van

[StarBear]

(IMG:style_emoticons/default/pray.gif)

[emerygt350]

That sounds like a good start! I would not be surprised if that points issue was causing issues.

[Van B]

@emerygt350
Me either. That would bring the total of main contributing causes to three:
-Malfunctioning injectors causing a dead cylinder on cold starts
-Bad TTS not providing signal for full fuel from CSV
-Points drift or binding on cold start

Honorable mentions would be:
-incorrect spark plugs not seating
-multiple vac leaks (lines and intake boots)


But I have yet to see if what happened today is repeatable so, I won’t allow any optimism just yet lol…

[wonkipop]

f-en weird.

i did not try repeated cranks on mine cold - test 1.
might redo test 1.

though starbears is very similar to mine on the first time it started - about 10 seconds.
sb's would have taken those six cranks to build fuel pressure from cranking as it had been sitting a while? the running for 10 seconds bit is exactly like mine.
i just didn't do the repeated cranks after 30 seconds - so who knows, mine might do that from cold. wouldn't do it warm though.

i was going to ask you van if your fuel pump had been moved.

steve - has your fuel pump been moved up front.

mine is in original spot.
but is a new fuel pump - turbine two port.
but i don't believe we rewired anything.

[wonkipop]

it sounds like you might have cracked it with yours van.


steve's could not have run for 30-40 seconds with residual fuel pressure could it?
thats a bit long or is it possible?

wonder if you did some kind of equal to a reboot van. (IMG:style_emoticons/default/smile.gif)
i remember we had to do it all the time with our old 486 computers back in the 90s.
residual errant voltages etc. electricity.

its a funny zone it operates in at cold start is what i now realise.
the afm is definitely being operated by the stator flap with the aav open?
and at the same time the throttle has the idle switch on in that position.
- in some way they are interacting? or handing off to each other?

all of our cars were definitely getting injector commands off the throttle switch?
the test showed they were the same in that way.
how long they ran had something to do with state of tune, fuel pressure/or not, state of info coming in from cht etc but nothing from the afm.

[StarBear]

f-en weird.

i did not try repeated cranks on mine cold - test 1.
might redo test 1.

though starbears is very similar to mine on the first time it started - about 10 seconds.
sb's would have taken those six cranks to build fuel pressure from cranking as it had been sitting a while? the running for 10 seconds bit is exactly like mine.
i just didn't do the repeated cranks after 30 seconds - so who knows, mine might do that from cold. wouldn't do it warm though.

i was going to ask you van if your fuel pump had been moved.

steve - has your fuel pump been moved up front.

mine is in original spot.
but is a new fuel pump - turbine two port.
but i don't believe we rewired anything.

Yes, moved mine to the front a few years ago. A trusted mechanic so doubt it was wired differently.

[wonkipop]

f-en weird.

i did not try repeated cranks on mine cold - test 1.
might redo test 1.

though starbears is very similar to mine on the first time it started - about 10 seconds.
sb's would have taken those six cranks to build fuel pressure from cranking as it had been sitting a while? the running for 10 seconds bit is exactly like mine.
i just didn't do the repeated cranks after 30 seconds - so who knows, mine might do that from cold. wouldn't do it warm though.

i was going to ask you van if your fuel pump had been moved.

steve - has your fuel pump been moved up front.

mine is in original spot.
but is a new fuel pump - turbine two port.
but i don't believe we rewired anything.

Yes, moved mine to the front a few years ago. A trusted mechanic so doubt it was wired differently.

van should be able to spot his.
if its running off the ignition circuit source only, it will be running with the key on.
be the same for you. if its in a spot where you can easily listen for it you can run that little test.

mine definitely does not run with the key in the on position before i crank.
so i know its working like it originally was supposed to.
its in fact right under me with my right hand drive.
i can hear it easily when its working hard on a hot day.

and thinking about it, you have a lot more fuel volume at that pressure that takes longer to bleed off? might explain why it could run for a bit longer - but not sure about that.
emery might have a better idea.

i sure do not have that volume of fuel at full pressure to bleed off. just the injector circuit and short line from the pump.