1974 1.8L engine fast idle then stalls, Fuel injection issues Options

[tshih914]

Wonkipop. I agree that the TPS may be an issue or even the ECU, but he’s got to solve the obvious issues first… control the variables. In general, people’s approach trouble shooting cars loke theres an OBDII port and a code to read. But we’re talking about an open loop vacuum system. And computers that are little more than if/then statements as code.

-Fix all potential vacuum leaks
-confirm baseline settings
-confirm fuel, air, spark per cylinder
-confirm timing (difficult to do at this point without a stable idle)

We’re doing a whole lot of talking in thinking without much information at this point. You already said it, @tshih914 has got to get methodical. Four pages into this thread and the airbox lid just now being removed is a SMH moment for sure.

Took the throttle body off to inspect and clean the mating surfaces and replaced the seal. The pin hole is clear of any obstruction and was attempting to check the plug harness for continuity at pins 2, 18, 2 to ECU. However the 2 10 mm bolts at the ends of the harness just spins freely without the bolt backing off. I suppose I have to cut the heads off inorder to get access to the pins at the ECU end of the harness.

[wonkipop]

nuts do not release harness plug.

this is how you do it.
press down on the little spring clip.
this will release the bottom of the plug.
pull + swing it out from there, it will pivot on its upper hook connection.
once swung out far enough pull downwards off the hook.




all this is described in factory workshop manual.
have you downloaded it from the links i gave you back on page 1?
it will tell you how to do all these things without breaking anything.


the nuts hold the ECU into its support sleeve.
which should be fixed on to the edge of battery tray.
this does not seem to be the case with yours?
the ECU is just laying around in there?
the nuts have probably stripped the thread in the support sleeve.
the sleeve is made of plastic and is delicate.
EDIT, its been a while since i had my ECU out to clean around in that area.
i got the ECU out of that sleeve and i seem to remember those bolts are captured.
once you undo them a certain amount the ECU just slides out of sleeve.
i could be wrong, its been a while. but irrelevant to releasing the plug connector.

you missed inspecting the throttle position switch. TPS.
and testing it?
its connected to the underside of the throttle body.
checking whether you hear click of switch when you open t/b from closed.
but we can return to that.

[wonkipop]

take a photo of the ECU pins and harness plug when you have them apart and post it.

be delicate with it all. it looks like it might not have been off for a long time maybe.
so just go easy at it.

[wonkipop]

Wonkipop. I agree that the TPS may be an issue or even the ECU, but he’s got to solve the obvious issues first… control the variables. In general, people’s approach trouble shooting cars loke theres an OBDII port and a code to read. But we’re talking about an open loop vacuum system. And computers that are little more than if/then statements as code.

-Fix all potential vacuum leaks
-confirm baseline settings
-confirm fuel, air, spark per cylinder
-confirm timing (difficult to do at this point without a stable idle)

We’re doing a whole lot of talking in thinking without much information at this point. You already said it, @tshih914 has got to get methodical. Four pages into this thread and the airbox lid just now being removed is a SMH moment for sure.

yes to all.

thats why i was keen for him to see if he could at least bring the idle down a little with the idle screw and the errant AAV and decel out of the picture and isolated.
its important to know if he can affect the idle with the screw at all and start to get something like a lower steady idle close or closer to normal.
or is the whole thing still being overwhelmed by another air leak that has not been found.

------

i think the TPS needs close inspection.
electrical test to see if its working.
and the mechanical test to listen for the audible click from the switch as the throttle is closed.
there is the ability to adjust its position with the fixing screws.
so that it can be put back in spec mechanically if its ok inside electrically.

they are vulnerable to filling with gunk as the car ages.
similar to the wear bushing problem of the throttle body itself.
the o-ring seal goes between t/b and TPS. lets condensed crankcase vapors etc gradually build up inside it if it can get in there.
its one of the faults of choosing a vertically alligned throttle plate pivot.
a lot of other manufacturers used a horizontally alligned throttle pivot with TPS off to one side rather than at bottom. a slightly friendlier position.

TPS must be fully ticked off.
its not a hard test to do.
you have to be able to trust each of these things by checking them one at a time.

we have to be sure the ECU knows when the throttle is closed so it can operate correctly on its idle circuit (or mode whatever you want to call it in one of these old analogue devices). .........as part of getting to a basic timing setting/adjustment.
we also need to know if the switch is doing its job to let the ECU know the throttle has opened. then we can trust it and move on.

[tshih914]

Thanks wonkipop for saving my bacon and not butchering the ECU mount. I have followed your instructions and got the cable opened up without damaging it. I have also learned how to post a video on my Youtube channel https://www.youtube.com/shorts/HT8ScUYyYdw showing the throttle switch making the clicking sound for what its worth. Next I will use a ohm meter to check continuity of cable pin #3, 18, and 2 from throttle valve cable to ECU harness pin(which number pin corresponds to those connected to the valve?)

[tshih914]

Thanks wonkipop for saving my bacon and not butchering the ECU mount. I have followed your instructions and got the cable opened up without damaging it. I have also learned how to post a video on my Youtube channel https://www.youtube.com/shorts/HT8ScUYyYdw showing the throttle switch making the clicking sound for what its worth. Next I will use a ohm meter to check continuity of cable pin #3, 18, and 2 from throttle valve cable to ECU harness pin(which number pin corresponds to those connected to the valve?)

I went to the manual and checked the wiring diagram which shows wires # 9, 20, and 17 which I think corresponds to pin # 3, 18, and 2 . Would someone provide the key for the pin position at the attachment point to the ECU for me to identify pins 9, 20 and 17.

[wonkipop]

thats great about the tps making the clicking sound.
it should do it just as you crack open the throttle and just as its closing.
sounds like its ok.
you can do an electrical test on it too.
to confirm it all.
but it sounds like you can tick that off. (IMG:style_emoticons/default/beerchug.gif)

i'll have a look later and see if i can find the pin diagram for the ECU and post it.
with a bit of luck someone else might post it for you before i get hold of it.

[bob164]

Jeff Bowlsby's excellent website has a "914 Tech Notebook " section.

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

The ECU Connector pin-out is on page 22 of the "Technical Manual L-Jetronic Fuel Injection System".

Hope this helps,
Bob

[wonkipop]

ah good.
@bob164 has given you the links.

in case you can't stumble on it.

here





(IMG:style_emoticons/default/beerchug.gif)

BTW i always had the battery disconnected when i pulled that ECU plug.

[wonkipop]

by the way i think i have had a thought about how this thing is actually running.
@Van B can offer his criticism on my ridiculous idea? (IMG:style_emoticons/default/biggrin.gif)
or any one else for that matter.

i don't think its starting and going to "idle" with the usual assistance of say the cold start injector etc. ie a normal start to a fast warm up idle. hence the hard starting.

nor do i think the original description of high idle at 3000 rpm is correct.
thats not an idle. thats what we used to call an engine that was "racing".
its half way to red line!!!

i think this thing might actually have been permanently in the twilight zone of thinking it was deaccelerating. with enough cranking, it sprayed enough juice in there to finally fire.
and once it fired with all the air it was getting from the faulty deacceleration valve and AVV it went straight to stuck wide open decel valve mode. 3000 rpm and stayed there.
because it can? there is no fuel cut off at throttle close off from high revs in an L jet except via the AFM flap. and if fuel cut off does happen it only happens if the afm flap descends past the point where the contacts are to activate the f/p. (why the decel is there in an L jet in the first place, to stop that). i put a proviso on that of course, it will only cut off the fuel if the fuel pump is properly wired to AFM control as it is stock.

i'll think more about this.

but in summary so far.

car:

1) starts with difficulty. (something is amiss in the cold start set up).

2) when it starts runs in jammed decel mode with tps indicating idle position and communicating closed throttle but AFM flap at elevated point on arc of contacts.
(which is a perfectly legit situation for L jet - although usually only momentary ).
its kind of a zombie?

beyond that i can't think whats going on when you try to gas it.

everything has to be properly set to really test transition to opening throttle.
valves adjusted.
points. timing (including dist advance function checked).

we know its got legit fuel pressure.

anyway its just a thought at this stage and further testing of components has to be done.

the cold start injector and the thermo time switch that controls it need checking in relation to hard starting.

[tshih914]

I tried to check the wires from the throttle valve switch pins 3,18,and 2 for continuity at the 2 ends (ECU and valve) as shown in the 3 photos. Meter set for audible beep and there was no sound. Am I doing the test correctly?

photo below testing pin #2 to #2 on ECU end

[tshih914]

Between pins #3

[tshih914]

testing pins #18

[wonkipop]

you operate the throttle while doing the test.
and thats

1) testing the switch itself.

and then

2)
if you want to test the connection to the ECU you need that plugged back in and test it at the ECU plug pins.

is that what you are doing?


--------

[wonkipop]

@Van B

i spoke to mike this morning.
as i thought the AFM will run the engine according to where the flap is and the ECU will provide the fuel, no matter the throttle switch saying its in idle.
it accepts the inputs. despite the real throttle being closed and the psuedo throttles open (the decel and aav). both of these are acting as "metered air".

he doesn't think that is why it stumbles when you open the throttle.

[tshih914]

[quote name='wonkipop' date='Mar 8 2023, 05:17 PM' post='3063545']


you operate the throttle while doing the test.
and thats

1) testing the switch itself.

and then

2)
if you want to test the connection to the ECU you need that plugged back in and test it at the ECU plug pins.

is that what you are doing?

Initially , no. When I did as you described the throttle switch test pass when the throttle was opened sufficiently for there to be continuity between pins 18 and 3.

2) when plugged in there was continuity between pins 2 or 3 with 18when throttle is fully closed.

[wonkipop]

here is a y t vid i came across a few years back on t p s for L jet.
he opens one up so you can see how it all works.
including the type that is on the 914.

https://www.youtube.com/watch?v=WHoeE81ZcHU

[Van B]

@Van B

i spoke to mike this morning.
as i thought the AFM will run the engine according to where the flap is and the ECU will provide the fuel, no matter the throttle switch saying its in idle.
it accepts the inputs. despite the real throttle being closed and the psuedo throttles open (the decel and aav). both of these are acting as "metered air".

he doesn't think that is why it stumbles when you open the throttle.

Our TPS really only tells the ECU to send fuel for idle, neutral for driving range, and then enrichment for wide open.

[tshih914]

here is a y t vid i came across a few years back on t p s for L jet.
he opens one up so you can see how it all works.
including the type that is on the 914.

https://www.youtube.com/watch?v=WHoeE81ZcHU

The inside of my TBS is reasonably clean and it passed the test of throttle opening resulting in 0 ohms resistance when throttle is opened. So the racing/idling at 3000 rpm with throttle fully closed is indication of what's not working correctly?

What component should we test next?

[wonkipop]

CHT

cylinder head temp sensor.


after that pull the AAV off. Aux Air Valve.
clean it out. carb cleaner is good. get it thoroughly cleaned out.
probably full of gunk.
put it in the freezer/cold fridge for half an hour after you have cleaned it.
see if its (EDIT) open. you look down the bore and hold it up to the light.
if it is (EDIT) open hook it up to a 12V source. like a car battery for instance.
after 5 minutes or so on the current it should be closed. or very nearly closed.
hold it up to the light again and inspect to see if thats the case.

basically you should be testing everything on the EFI.
everything.

then the ignition. in particular the distributor.

you need to be sure everything is working.

while you wait to get your hoses and seals.

the ECU is the hard one to really know.
you still have not answered my question.
how long has it been lying around loose in the engine bay.
the plastic sleeve you almost went hammer and tongs at provides it with an isolated mounting so its never lying on anything hot or subject to random electrical shocks etc.
?


we have already explained to you why it was racing at 3000 rpm.
its pulling air through the decel valve and the AAV.
this is metered air, not air leaks. ie those malfunctioning components were pulling the afm flap open just the same as if you had the throttle opened.
you (or someone before you?) had screwed the throttle idle screw right down hard closed to try and calm it down. your car has never been idling in that state.
its been racing with a psuedo throttle open.
the timing is probably out. etc.

what we don't know is why it stumbles when you open the throttle.
although there was a clue when you did one of the tests i suggested to close off the decel and AAV hoses and you reported it almost did not stumble over when you opened the throttle. unless i misread your report.
this might offer you some hope.
i could guess the stumbling might be in part antagonised by some further genuine air leaks in the system. ie air which is not pulling the flap open in the AFM but causing the mixture to lean out. but i am really not sure. its impossible to know until the entire system is verified. vacuum hoses, seals and all. its always been my experience that unmetered air leaks do not cause the engine to race, rather they cause it to be unstable and unsteady at idle and often mean it just dies and won't run.

the point you need to get to is a proper idle and a proper cold start.
by proper idle i mean an idle set off the t/b idle screw and with the ignition timing verified and properly set. thats step 1.
and you won't get there until you go right through the system.
by the end of it you will know every bit and what it does.