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> 1974 1.8L engine fast idle then stalls, Fuel injection issues
tshih914
post Feb 23 2023, 08:16 PM
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QUOTE(tshih914 @ Feb 23 2023, 05:58 PM) *

QUOTE(wonkipop @ Feb 23 2023, 10:00 AM) *

ok @tshih914

@Van B (i'm sure) and i would like you to do one more test.

pull the AFM plug out (you can pull it out up at the AFM unit on the aircleaner) and see it if starts and runs at this 3000 rpm. don't touch the gas pedal. just let it start on its own.

if it does start and run do a second thing.

turn if off, restart it without touching the gas pedal or throttle and then once its running again at this steady 3000 open the throttle to give it the gas and see what happens. again with AFM plug out.

report back on the result.
-------
@wonkipop The fuel pump was left as OEM stock just replaced the old fuel hoses to tank and line to engine.

I unplugged the AFM and the engine started after several attempts and started to idle around 1200 rpm initially then rose to 2000 rpm. Shut it off and upon restart while at 2000rpm try to give it gas it immediately stall. All the while unplugged so no AFM inputs

thanks for including the photos.
i am studying them trying to look at area between battery and firewall.
it looks like your ECU is not securely fixed but floating around in there.
its been rotated 90 degrees.
not that its necessarily the cause of your problem,
but @Van B (and i) are thinking of your ECU to AFM connection.
the test i have asked you to do is going to see if this is the problem.


-------

i can see from photos how you have rigged up the fuel lines.
looks fine. i can see most of your vacuum lines and they look right and looks like you have gone over them. i can even see the intake runners appear to have new or good condition woven seals. so all that looks pretty good for being tight and leak free.

its a good idea inserting a full flow high pressure fuel filter in the line like you have.
i have one too which i have installed in almost the same spot.
will save your injectors if you have a newer type fuel pump and it detonates internally.

which leads to the next question.

when this problem of more and more difficult starting first was happening, where was the fuel pump and what was it. original type pump under engine bay on rhs? with original electrical connection?

and did you install a new fuel pump with all your work on the fuel lines.
if you did, where is it, what type and how is it wired in to run?


The fuel pump is the original one that came with the car. Its in the front of the car under the fuel tank next to the brake master cylinder protected by the steel panel that,s bolted to the A-arms front torsion bar area.
I unplugged the AFM and the engine started after several attempts and started to idle around 1200 rpm initially then rose to 2000 rpm. Shut it off and upon restart while at 2000rpm try to give it gas it immediately stall. All the while unplugged so no AFM input
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wonkipop
post Feb 23 2023, 09:01 PM
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wow @tshih914

that was a quick test and reply.
we are making some progress.

first thing. fuel pump may be original or original type.
but its definitely not in stock position for a 74 L jet.

would appear its had the by now common modification of a move up to front of car under fuel tank to guard against vapor lock.
(the original stock position is right under the engine on right hand side tucked right up above the heater tube that goes into the longitudinal).

given the behaviour after you unplugged the afm its definitely not stock OEM wired in. i'd say its running off the ignition circuit.

i'd have to think about this a bit.
no doubt @Van B will come in again at some point.

but the behaviour with the AFM unplugged was not exactly the same as with it plugged in by the sounds of it. i would have expected it to be exactly the same if the fault or problem was that the AFM was not sending a signal and the car was just running off the fuel pump triggered by the ignition circuit and the throttle position switch at idle.

i'd probably think at this stage there was a signal getting through.

i'm going to go with the idea that the AFM signal is not a problem.

you should turn to the second test now.
pull the hoses off the decel valve and plug the hoses so it can't pull air.
try starting it. it should go. and idle should be reduced to level it was when you clamped the decel valve. but you might find the idle air screw is too closed and you might have to adjust that to get it to idle. its been getting a lot of air through that decel valve. but its not "leaking" air. it is actually metered air. it will have been pulling the AFM flap open. the AAV will have too. so this is not an unmetered air leak.

and then try gassing it after you have got it idling.
this should be a good test for @Van B 's thinking its falling over because it leans right out the minute you open the throttle.
see what happens and let us know.
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Van B
post Feb 23 2023, 09:41 PM
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Definitely sounds like the AFM is doing stuff… but also, you can’t have that idle screw all the way down. You won’t idle like that. Put it two turns out and leave it there till you’re ready to set it up correctly.

Ref the video I made for you, remove the vac hose on the decel valve that runs from the side of the valve to the manifold. Block off the manifold and the port on the decel valve. Leave everything else connected for the moment.

Give it a start and lets see how it behaves.

Also, please post up your door placard so, we can confirm your mfg date.
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tshih914
post Feb 25 2023, 04:35 PM
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QUOTE(Van B @ Feb 23 2023, 07:41 PM) *

Definitely sounds like the AFM is doing stuff… but also, you can’t have that idle screw all the way down. You won’t idle like that. Put it two turns out and leave it there till you’re ready to set it up correctly.

Ref the video I made for you, remove the vac hose on the decel valve that runs from the side of the valve to the manifold. Block off the manifold and the port on the decel valve. Leave everything else connected for the moment.

Give it a start and lets see how it behaves.

Also, please post up your door placard so, we can confirm your mfg date.


Did as instructed I opened the idle adjustment screw 2 turns and after cranking a bit the engine started with a rough idle then stayed around 2000-2500 rpm. Again when gassed the rpm drops to almost stall but when I release the throttle it would idle back up to 2500 rpm. After 2 stabs of the throttle it finally stalled. I 've included the photos of the blocked off manifold T and side of Dcel valve along with the door label showing a Jan.1974 build date.


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tshih914
post Feb 25 2023, 04:36 PM
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QUOTE(tshih914 @ Feb 25 2023, 02:35 PM) *

QUOTE(Van B @ Feb 23 2023, 07:41 PM) *

Definitely sounds like the AFM is doing stuff… but also, you can’t have that idle screw all the way down. You won’t idle like that. Put it two turns out and leave it there till you’re ready to set it up correctly.

Ref the video I made for you, remove the vac hose on the decel valve that runs from the side of the valve to the manifold. Block off the manifold and the port on the decel valve. Leave everything else connected for the moment.

Give it a start and lets see how it behaves.

Also, please post up your door placard so, we can confirm your mfg date.


Did as instructed I opened the idle adjustment screw 2 turns and after cranking a bit the engine started with a rough idle then stayed around 2000-2500 rpm. Again when gassed the rpm drops to almost stall but when I release the throttle it would idle back up to 2500 rpm. After 2 stabs of the throttle it finally stalled. I 've included the photos of the blocked off manifold T and side of Dcel valve along with the door label showing a Jan.1974 build date. The "idle" speed does not seem to be changed by turning the screw



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wonkipop
post Feb 25 2023, 05:56 PM
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@tshih914

we are getting somewhere.
this time it did not stall, it almost stalled, but did not stall.
it did try to do the transition to open throttle.
not very well. but it showed hopeful signs! (IMG:style_emoticons/default/smile.gif)

the first time you sealed off the decel hoses it dropped to 1000, much lower than the 2000-2500 with this test. that was because in the first test the idle screw was closed completely shut. the engine was getting a significant portion of its air from the decel valve. to the tune of about 2000 rpms worth. now some of that air that was being supplied by the decel for the elevated revs is being supplied by the idle air passage being opened up.

the auxiliary air valve is probably supplying some rpms worth going by the tests.
when you pinched that one shut in the earlier isolation test you said the rpm dropped but you did not say by how much. if it was in proper working order it would have been in the order of 400-500 rpm worth stone cold. getting less as it warmed up and closed.

from here you really have to go through each component one at a time and test them.
you will need that factory manual i gave link to in page 1 of this topic.
you only need section 1 (engine) and section 2 (EFI).

it will be interesting to hear from other members.
there are some very knowledgable L jet guys on the site.
@Van B will likely have something to say now that could be useful.

i'm going to think about it a bit more.


EDIT
thanks for the VIN label. its built the week before mine.
got the same brown interior.
when we get to the end of this and hopefully get the old girl running i'll ask a favour of you for some archival info, but not now, lets get her going. (IMG:style_emoticons/default/beerchug.gif)
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Van B
post Feb 25 2023, 06:45 PM
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@tshih914

The decel valve is on the other side. I can’t exactly see what you’ve done in the photo but I see an open hose. Is that coming from the aux air regulator?
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Van B
post Feb 25 2023, 06:49 PM
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Yeah this is all wrong. You’ve got the wrong part. You capped off the Y where it attaches to the aux air valve/regulator inlet, but then left the AAV open… which is allowing unmetered air into the manifold.

You need to put all that back together.

Watch my video again and go over to the passenger side and find the decel valve. That’s what we’re trying to get capped off.
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wonkipop
post Feb 25 2023, 07:22 PM
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@Van B .

i think he has got it right.
he seems to have removed the hose between the decel valve and the Y junction.
the route for air to be drawn into the decel valve.
and he has capped the decel valve and the Y junction.
which means the decel valve can't draw air and the boot is sealed.
thats if i am reading his photo correctly?

i don't see any uncapped hoses to plenum in the photo.
so long as he has taken the hose out i understand he has it should be isolating the decel and stopping the air route and not leaving anything open.



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wonkipop
post Feb 25 2023, 07:26 PM
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i think he has pulled this hose out and capped the Y and decel at where it joined them.

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wonkipop
post Feb 25 2023, 07:44 PM
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where i am going with my thinking @Van B is

1. to get this poor old girl to idle without either the decel valve or the AAV being part of the picture. neither are needed for normal warm idle.

2. to see if he can get a warm idle using the idle screw. at around 1000 rpm.

3. do the gassing thing.

trying to get this high idle thing out of the picture if possible.

realise there are a whole lot of things need for stable warm idle.
not least
correctly adjusted valves.
correctly set timing.

if it won't transition to opening the throttle from that state of warm idle.
well?
there is a few thoughts that come to mind.

also if he can't get it down to stable low warm idle and it starts to hunt around as you screw it down it could indicate there are some air leaks. and these will be unmetered air leaks. but want to get these "legit" air routes out of the picture because they are masking whether it will do a normal warm idle.
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Van B
post Feb 25 2023, 07:54 PM
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Looks to me then like the decel valve is connected opposite of mine and he hasn’t unplugged the decel line to the manifold but rather the bridge line from the intake to the valve?

See my mark ups below and tell me if I’m seeing it right?

Also, there is kink in the small line.


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wonkipop
post Feb 25 2023, 08:29 PM
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@Van B .

yes i noticed that kink in the small vac line to the decel.


i think he has only vac line 9 off. bridging line as you call it. and has capped off the connection points. so long as he only has that line off he is alright.

attached pic of set up for vac lines to decel.
but to be honest i don't think it matters which of the large lines you plug in either to side or end. the small line is opening the decel valve and letting the air through.
i think it can work either way, but before i say that i better double check.
(if yours is the other way around from diagram and attached photo it would tend to prove it does work either way, since your valve is operating beautifully anyway!! (IMG:style_emoticons/default/biggrin.gif) )
however most cars are rigged the way it is in the vac hose diagram.
attached example.
which appears to be how his is rigged.



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EDIT
but you might be on to something there with the decel.
i can't really see in to his photo clearly enough.

@tshih914 , can you take a photo in close to the decel valve so we can see it really clearly.
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wonkipop
post Feb 25 2023, 08:56 PM
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i just watched your video @Van B .
your decel is rigged right or at least same as diagrams and how it is normally done.

i'm looking at his and it looks the same.
from what i can see of it.
but it would be nice to see a close in photo just to be sure.
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r_towle
post Feb 25 2023, 09:03 PM
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When I am hunting for a failure in the vacuum system, which has many parts, I remove all vacuum lines and tape over all the ports at the plenum.

This takes the vacuum out of the triage.
This also takes any hose out of triage.

Get the car running at idle (it needs no vacuum)
Add one vacuum line at a time, plugged into whatever device, properly.

Eventually you will create the issue again.

If you still have an issue after taking off all hoses and taping all ports closed, you could have an issue with a hole in the bottom of the plenum or your injector seals are leaking way too much.
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Van B
post Feb 25 2023, 09:19 PM
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74 L-Jetronic needs the distributor vacuum for anything but idle at operating temp when setting timing.

I just realized we haven't confirmed the turns on his idle screw at the TB!
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wonkipop
post Feb 26 2023, 12:37 AM
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QUOTE(Van B @ Feb 25 2023, 09:19 PM) *

74 L-Jetronic needs the distributor vacuum for anything but idle at operating temp when setting timing.

I just realized we haven't confirmed the turns on his idle screw at the TB!


he said he had it two turns out.
i imagine it was either already all the way down closed (which i think the introduction post said) or he at least turned it down to closed and backed it back up two full turns.

but i gather no further adjustment or attempt to bring idle down using it from there.

we probably will end up where r towle is suggesting we go!!!!
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nihil44
post Feb 26 2023, 01:43 AM
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I've come in late here and haven't read all of the posts.

Several times I have forgotten to replace the connector on the AFM with the result that it would start normally but stall as soon as you hit the gas. Similar symptoms as described in this post.

Secondly, I had a problem with the car stumbling when I went over a bumpy surface or railroad tracks. I discovered that, although the AFM appeared to be connected, the connector was not seating all the way home and was going intermittently open circuit when disturbed by the bumps

On exploration I discovered that the AFM connector has a rectangular foam rubber seal around the periphery of the row of 7 pin connectors to prevent water ingress but the seal was preventing the connector from fully seating. I removed the seal and the connector clicked fully home. Problem solved.

This might be worth a look
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wonkipop
post Feb 26 2023, 01:54 AM
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QUOTE(nihil44 @ Feb 26 2023, 01:43 AM) *

I've come in late here and haven't read all of the posts.

Several times I have forgotten to replace the connector on the AFM with the result that it would start normally but stall as soon as you hit the gas. Similar symptoms as described in this post.

Secondly, I had a problem with the car stumbling when I went over a bumpy surface or railroad tracks. I discovered that, although the AFM appeared to be connected, the connector was not seating all the way home and was going intermittently open circuit when disturbed by the bumps

On exploration I discovered that the AFM connector has a rectangular foam rubber seal around the periphery of the row of 7 pin connectors to prevent water ingress but the seal was preventing the connector from fully seating. I removed the seal and the connector clicked fully home. Problem solved.

This might be worth a look



(IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif)
yeah nihil we put him through that test - did not seem to be his problem.

good suggestion however to look at that seal.
his connector will be a 6 pin version.

ah. the joys of prehistoric EFI! (IMG:style_emoticons/default/beer.gif)

by the way, hows your car going mate?
got to get up to brizzy at some stage and drop in on you. (IMG:style_emoticons/default/beerchug.gif)
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Geezer914
post Feb 26 2023, 06:12 AM
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Last resort is to do a smoke test. Search on you tube on how to build one for under $20. You will find the vacuum leak.
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