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> 1974 1.8L engine fast idle then stalls, Fuel injection issues
tshih914
post Feb 19 2023, 11:45 PM
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My 1.8L 914-4 with stock Bosch L?-Jetronic FI after being stored several years started to develop a hard to start problem. When finally started would stall when I give the gas pedal any input to raise the revs. I suspect there was some kind of intake air leak and while fiddling around had a backfire which blew the AF meter which I had Pelicanparts repaired. After replacing the fuel lines with the stainless ones from Tangerine Racing and flushing out the fuel system with Techron the engine started to run normally for a short time. Now the engine can be started and fast idles at 3000 rpm but again any input to rev up the engine results in stalling. The idle adjustment screw at the base of the throttle housing is fully closed. Any suggestions on how to fix?
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Van B
post Feb 20 2023, 01:28 AM
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Check to make sure your AFM is plugged in first.
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wonkipop
post Feb 20 2023, 01:38 AM
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QUOTE(Van B @ Feb 20 2023, 01:28 AM) *

Check to make sure your AFM is plugged in first.

(IMG:style_emoticons/default/agree.gif)

sort of sounds like its not connected maybe?
moving throttle plate takes throttle position switch off idle position and hands off to AFM.
except AFM might not be there.

check that first.
then troubleshooting step by step can commence.
sounds like this problem was already there before you had unfortunate backfire and wrecked the AFM. kind of pointing at maybe a problem in the harness? or somewhere in the hand off between the TPS and the AFM.
anyway its got to be done methodically.


fast idle is likely a separate problem. maybe.
one step at a time.
save that for later.

what 1.8. 74 or 75?
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Geezer914
post Feb 20 2023, 06:48 AM
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1+ on the AFM not being connected. Check for vacuum leaked. The intake boot may have a crack.
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tshih914
post Feb 20 2023, 11:02 AM
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QUOTE(Geezer914 @ Feb 20 2023, 04:48 AM) *

1+ on the AFM not being connected. Check for vacuum leaked. The intake boot may have a crack.


I assure all that the AFM is plugged in and my fuel pressure gauge reads 28psi. One other piece of info is when the engine is "idling" at 3000 rpm I placed my hand to cover the nozzle of the air box housing feeling for vacuum from the air passing through the air filter into the AFM and felt little air flow! This means that there is an air leak (like when you adjust the idle by opening the screw at the base of the throttle to bypass the AFM). I had replaced the intake boot when the initial problems showed up. When searching for vacuum leaks there are lots of hoses and connections and even the O-ring gasket under the oil filler cap to check. Also is there an auxiliary air flow sensor in the 1974 1.8L FI system?
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dr914@autoatlanta.com
post Feb 20 2023, 11:17 AM
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for the hell of it check the throttle body boot for cracks
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rhodyguy
post Feb 20 2023, 01:22 PM
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Would a vacuum leak down stream of AFM result in a low idle not a high one?
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wonkipop
post Feb 20 2023, 02:17 PM
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QUOTE(rhodyguy @ Feb 20 2023, 01:22 PM) *

Would a vacuum leak down stream of AFM result in a low idle not a high one?


thats been my experience.
air leaks usually mean it won't idle at all or it will have an unsteady idle and hunts around. air leaks won't pull the AFM flap, so usually they lean out.

@tshih914

these are handy if you don't have them.
factory workshop manuals.

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

you may as well download them all (except 914/6 specific).
fuel injection = group 2.
has all the trouble shooting checks for each L jet component.
its a bit tricky to read as its mixed in the with D Jet stuff.

back to high idle, i suspect this is the decel valve.
its come up before with two other members.
fits the pattern. idle stuck at 3000 rpm.
i'd have to dig up the thread.
but @Van B can probably find it easily, he was the original poster for one of them.
or he can lay out the precise process for testing the decel valve to see if its good,
and also to adjust it. the decel valve is adjustable.
its diaphragm has probably stuck.
the air route through the decel valve will pull the AFM flap and let the ECU know its wanting the fuel to match the air. even though the throttle position switch is letting the ECU know the throttle is closed and at idle position. in other words it is perpetually stuck at halfway down from open throttle to closed throttle.


accurate vacuum hose layouts are here on page 3 of this thread.

http://www.914world.com/bbs2/index.php?sho...57407&st=40

for 74 models.
you can check your vacuum hose set up just to be sure.
but i don't think its going to be an air leak that is causing the high idle.
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wonkipop
post Feb 20 2023, 02:33 PM
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QUOTE(tshih914 @ Feb 20 2023, 11:02 AM) *

QUOTE(Geezer914 @ Feb 20 2023, 04:48 AM) *

1+ on the AFM not being connected. Check for vacuum leaked. The intake boot may have a crack.


I assure all that the AFM is plugged in and my fuel pressure gauge reads 28psi. One other piece of info is when the engine is "idling" at 3000 rpm I placed my hand to cover the nozzle of the air box housing feeling for vacuum from the air passing through the air filter into the AFM and felt little air flow! This means that there is an air leak (like when you adjust the idle by opening the screw at the base of the throttle to bypass the AFM). I had replaced the intake boot when the initial problems showed up. When searching for vacuum leaks there are lots of hoses and connections and even the O-ring gasket under the oil filler cap to check. Also is there an auxiliary air flow sensor in the 1974 1.8L FI system?


there is no auxiliary air flow sensor in the L jet.
but there is a cold start aux air flow valve. AAV.
provides extra air to the engine during cold start.
but its connection is in the boot and after the AFM flap.
so it causes the AFM flap to deflect and for the car to receive extra air bypassing the closed throttle. there are two other sensors to measure temp. the main one at a cold start is the cylinder head temp sensor telling the ECU the engine is cold. i doubt the AAV will cause of the 3000 rpm high idle. it will raise the idle if its stuck open but not usually to that extent. not from stone cold anyway.

its a matter of downloading the manual and testing each component methodically 1 by 1.

i'm not sure exactly what is causing the engine to die when you gas it for revs.
apart from the AFM not communicating properly with the ECU.
i've got some other L jet diagnostic manuals. i'll look through them to see if thats a specific fault mentioned. as you mentioned - you had this fault initially before AFM explosion. so its something there you have not found yet despite the rebuilt AFM unit.

i don't want to speculate too far, but one of the components on the check list will the throttle position switch. i'd have to read further on what that might lead to if its faulty or not operating correctly.
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Van B
post Feb 20 2023, 02:51 PM
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QUOTE(tshih914 @ Feb 20 2023, 12:02 PM) *

QUOTE(Geezer914 @ Feb 20 2023, 04:48 AM) *

1+ on the AFM not being connected. Check for vacuum leaked. The intake boot may have a crack.


I assure all that the AFM is plugged in and my fuel pressure gauge reads 28psi. One other piece of info is when the engine is "idling" at 3000 rpm I placed my hand to cover the nozzle of the air box housing feeling for vacuum from the air passing through the air filter into the AFM and felt little air flow! This means that there is an air leak (like when you adjust the idle by opening the screw at the base of the throttle to bypass the AFM). I had replaced the intake boot when the initial problems showed up. When searching for vacuum leaks there are lots of hoses and connections and even the O-ring gasket under the oil filler cap to check. Also is there an auxiliary air flow sensor in the 1974 1.8L FI system?


You covered the snorkel completely and the car kept running??

Here check this out to help you at least get a baseline on your connections:

https://youtu.be/ToxifurNXXg


https://www.youtube.com/watch?v=ToxifurNXXg


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Van B
post Feb 20 2023, 02:57 PM
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@wonkipop What alerts me is the no change in idle with the snorkel completely covered. I made that video because this thread reminded me that I should post this up for future reference.

Let’s confirm connections first and then see what’s working and whats not.

@tshih914 , the high idle started after you made repairs to the car? You said in your original post that it ran normally for a bit. What happened between then and now?

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wonkipop
post Feb 20 2023, 03:20 PM
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QUOTE(Van B @ Feb 20 2023, 02:57 PM) *

@wonkipop What alerts me is the no change in idle with the snorkel completely covered. I made that video because this thread reminded me that I should post this up for future reference.

Let’s confirm connections first and then see what’s working and whats not.

@tshih914 , the high idle started after you made repairs to the car? You said in your original post that it ran normally for a bit. What happened between then and now?


i read that as feeling around for airflow at snorkel rather than putting his hand over it and closing it off? engine should die if its closed off i agree.

nice little video. all there.
its an EC-B too. (IMG:style_emoticons/default/biggrin.gif)
with the vac advance line from distributor to throttle body.
EC-A won't have that. nor a 49 state 75. just the retard vac line in those.
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Van B
post Feb 20 2023, 03:33 PM
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Yeah, I know, but I don’t care about California emissions lol
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wonkipop
post Feb 20 2023, 03:49 PM
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QUOTE(Van B @ Feb 20 2023, 03:33 PM) *

Yeah, I know, but I don’t care about California emissions lol


(IMG:style_emoticons/default/biggrin.gif)
just in case @tshih914 has got a retarded (nation of california) engine and sees a hose that isn't there thats been holding him back for 50 years. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif)

we need to stick that video over in the 1.8 thread in originality.
its 101 L jet vac hoses for compleate idiots and 100% correct,
for idiots like me 5 years ago.

i noticed you carefully waved your hand in the general direction of the "dreaded"charcoal can! (IMG:style_emoticons/default/biggrin.gif)
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jim_hoyland
post Feb 20 2023, 03:52 PM
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Get that VIN ?
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All the above; L-Jet requires that there are no vacuum leaks. I found the small hoses were first to go, even a T connecting them became brittle and broke.
To test the small hoses, try bending them between your fingers. That’s how I found the leaks.
Subsequently, I placed an in-line Vacuum gauge in one of the larger hoses
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wonkipop
post Feb 20 2023, 04:13 PM
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@Van B

thinking about his problem there are two tests he can do right now without fiddling with anything or altering things as they stand. given the engine starts and fast idles at 3000 rpm. its obviously getting fuel at crank and at idle. and plenty of air.

1. before starting check the operation of the throttle valve. move it around by hand and make sure it is moving freely and resting right back at closed position.

2. start it up and let it settle at its 3000 rpm.

3. clamp off the vac hose tightly shut between decel valve and intake plenum.
note what happens if anything. does idle change. (make sure you clamp the right hose, its the one that comes out of side of decel valve and goes to intake plenum EDIT - sorry it comes out of end of decel and goes to plenum - it operates the valve off vacuum, but thinking about it you can also clamp off the hose that comes off side as its getting the air from the intake boot, so either of those can be clamped off shut).

4. unclamp hose. let engine return to 3000 rpm if it did change.

5. clamp Aux Air Valve hose tightly shut between end of AAV and intake boot.
(clamp it before it gets to the Y junction into boot as you want to isolate the AAV. - the other hose off Y junction is going to the decel valve).
note what happens if anything. does idle change.

Refer excellent video by prof Van B of hoses posted above to know which hoses referred to.

report results of 3 and 5 back here.

------
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Van B
post Feb 20 2023, 04:24 PM
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Boy does that all sound familiar.

I’d still like to know what changed from when it ran normal.
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wonkipop
post Feb 20 2023, 04:39 PM
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QUOTE(Van B @ Feb 20 2023, 04:24 PM) *

Boy does that all sound familiar.

I’d still like to know what changed from when it ran normal.


it does sound a bit familiar, but not completely the same.

he said he left it to sit in storage for a few years.
something in there gave up the ghost during rip van winkle period.

they don't like sitting around.


EDIT - i seem to recall you ( @Van B ) got some weird thing where your 1.8 would run at 3000 rpm and not do anything else when you had something off. but its a couple of years ago and i can't find that thread anymore. maybe its my imagination and false memory? there was something i was asked to do by you and i think it was see if mine would start and run without the AFM plug in. mine would not. but yours would? and it was the way the fuel pump in yours had been wired in after moving to the front. mine is still stock and fuel pump is run off the AFM contacts after cranking phase. i could have this wrong. but yours would run and it ran at 3000 rpm? until you hit the throttle. my memory is not that good.

EDIT EDIT - can you see where i am going with this @Van B ?
we have to find your thread again and go through it.
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wonkipop
post Feb 20 2023, 05:11 PM
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QUOTE(tshih914 @ Feb 20 2023, 11:02 AM) *

QUOTE(Geezer914 @ Feb 20 2023, 04:48 AM) *

1+ on the AFM not being connected. Check for vacuum leaked. The intake boot may have a crack.


I assure all that the AFM is plugged in and my fuel pressure gauge reads 28psi. One other piece of info is when the engine is "idling" at 3000 rpm I placed my hand to cover the nozzle of the air box housing feeling for vacuum from the air passing through the air filter into the AFM and felt little air flow! This means that there is an air leak (like when you adjust the idle by opening the screw at the base of the throttle to bypass the AFM). I had replaced the intake boot when the initial problems showed up. When searching for vacuum leaks there are lots of hoses and connections and even the O-ring gasket under the oil filler cap to check. Also is there an auxiliary air flow sensor in the 1974 1.8L FI system?


BTW @tshih914 - thats not the fuel pressure test for L jets.
you are going to find the correct test in the links to the manuals i posted previous.
you are actually looking for 35ilbs pressure when you operate the AFM flap.
its all in the manual. you can also test flow which is important as well as pressure.
again all the manual. but that is jumping ahead at this stage.
you need those manuals. the fuel pressure regulator is non adjustable in the L jets.
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Van B
post Feb 20 2023, 06:45 PM
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@wonkipop . What he described is exactly what happened when I started the car and forgot to plug in the AFM. Steve tried it and the same thing happened for him. You tried it and it didn’t work. That’s when I realized my fuel pump wiring was wrong as yours was OE and Steve and I had a different setup from the relocation to the front.
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