924Board.org

[Beartooth]

Let us know what you find on those things, RVA. I'm betting there's some simple culprit lurking: so many things that it could be like a bad ground, loose wiring - on and on. CIS really hates old gas and contamination, so you might want to tear into that and clean it all out again. I found in resurrecting my 931 that'd sat with the fuel line undone that I got everything where it should be, only to have it go wrong again because a chunk of varnish broke free and plugged the WUR. On the distributor, I thought about responding, but would just be taking a shot in the dark. What I wonder is if there's a right way and a wrong way to assemble it, or if it's possible to mix and match in the wrong upper part to the shaft. It might still run with the rotor phasing that far off, but I'd think it would cause serious problems. I'd stick with the one that's closer to the alignment notch.
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1980 931 diamond in the rough

[RVA]

Thanks for all the replies, i will defenitly check all the things posted here that could be the problem. I also found a mechanic who will help me this saturday to see if he can find something, so i will post here if i have an update.

[RVA]

Spark plug pictures. They are quite black, that means engine is too rich right?
cilinder 1 and 2:


cilinder 3 and 4:


I also gapped them at 0.7 mm, they were at 0.6 mm before.

Also as for the other things mentioned in the replies.

Vacuum timing advance works, hose also in good condition. and i lubed the center piece.
As for vacuum leaks i didn't check it with a smoke tester because i don't have one as of now. But i did like triple check every single vacuum/air hose for cracks and potential leaks but everything looks good.

Anyways tomorrow ill start the car and try and make it run a bit leaner.

[RVA]

And forgot to mention i should probably do another csi fuel pressure test, i will do as soon as i can get a fuel pressure tester, last time i borrowed one so i don't have it anymore.

[morghen]

Your problem is in plain sight.
All plugs should look the same, if one isnt it means there is something different and likely wrong with that cylinder.
It could be that the cyl2 injector is stuck and either isnt delivering any fuel or is delivering too little or or its just pissing it rather than pulverising it.

I’d take the cyl2 injector out and with a sharp screwdriver gently lift that small conical difuser ar the tip of the injector..only lift it like a milimeter.
That difuser sometimes gets stuck/glued to the injector body so it either barely squirts fuel or just pisses it.
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https://www.the924.com

[924RACR]

Agreed, you've got one cylinder (probably 2 or 3?) not working worth a damn.

When the engine is running, if you disconnect the spark lead from the distributor cap the engine note probably will not change, proving this.

If the engine is running well otherwise, it'll still run decently on 3 cylinders. You do not have this... so you have more problems than just one dead hole.

But once you get the one missing cylinder back in play, then maybe you'll be able to get the rest of the system tuned better.

That's pretty black, quite rich, but trying to get it running/tuned properly on only three cylinders is a fool's mission... check plug/ignition function, maybe try messing with that injector as noted.

Worst case, try moving the plug or injector to another cylinder, see if the problem moves, that will help isolate the problem if you have a bad plug, injector, or ignition wire...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[RVA]

Did some injector testing again. Exaclty the same output on all 4 injectors.



Here is the injector spray pattern, its hard to see on camera but on camera it looks slightly worse than it really is in real life. however its still not the best spray pattern i have ever seen. Keep in mind these where cleaned and tested by a shop specialised in porsche 924. They told me they were OK.
Anyway let me know what you think: (this is cilinder 1 but they all looked the same)
https://youtube.com/shorts/qXn7ofVbTKU

Engine is running much better now than last week, because last week i had set spark plug gap at 0,6 mm by accident. Now its at 0,7mm which made a big difference.

Throttle response is pretty good now, above 1500 rpm it runs really well. This is the engine at idle which is still a bit rough but miles better than last week: https://youtube.com/shorts/uyFhww8V_rs

I made it run a bit leaner, didn't have time to get the plugs out again to see what they looked like unfortunatly but it doens't run as rich as before.

I am having some trouble te let it run well at idle, the idle adjustment screw didn't really seem to be doing anything at all honestly, so the way that i got it to idle in the video is not with the idle adjustment screw, i adjusted the trottle body starting position screw:

And one more thing, sometimes when i turned the car off i would hear a weird high pitched noise, i couldn't tell at all where it was coming from but i have a video of the noise, maybe someone recognizes it. I didn't seem to be electrical because it still heared the noise when i disconnected the battery.
https://youtube.com/shorts/uKH0voCT7Rw

But yeah definitly some good progress this week, really happy with that. Now i think its just a case of finding out why it still has some trouble at low rpm/idle.

[924RACR]

If the (correct) idle adjustment screw isn't making a difference, that's definitely making one concerned that there's vacuum leaks still to find and fix...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[RVA]

Yes that definitly a possibility, i will try to get my hands on a smoke tester.

[morghen]

Had a listen, it sounds like its missfiring.
Mine had a similar thing, turned out to be a bad ignition lead.
Do what Vaughan said, with the engine running pull one spark plug lead at a time and try to figure out which cylinder is problematic.

Then exchange that ignition wire with the one next to it and start the car..see if its the same cylinder or the same wire that causes the problem.
Do the same with the spark plug.

In between trials take out the problematic spark plug and dry it out over the gas-stove flame for a few seconds.
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https://www.the924.com

[RVA]

okay ill try that too when i have some time to work on the car again.

The weird thing is that at higher rpms, something like 1500/2000rpm minimum, the engine sounds really good and no misfires, but anyway i will try what you and Vaughan said.

[morghen]

In your video of testing out the injectors you lift the metering plate by hand, but you do so too much, at idle and under 2000rpm, especially under not much load that plate moves up 1-2mm...so how do your injectors work at that particular plate lift?
My bet is that one of them doesnt open at all or only dribbles some fuel in.

This can be because of a semi-stuck injector...you can take them to get ultrasonic cleaned.
This can also be because of ignition leads being bad, as on higher rpm you wont be able to distinguish the missfire unless on a dyno.
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https://www.the924.com

[RVA]

Its been a few weeks but i did some work on the car.

First thing i did was smoke test the intake, and i did actually find 2 small leaks. 1 at the fuel mixture screw, just put a rubber cap over the hole, and one in the intake where a hose was not sealing properly, so i fixed that. No air leaks anymore, double checked it.


I checked the injectors like you said morghen with only opening the metering plate 1-2mm, and fuel spray is fine. Injectors were also ultrasonic cleaned. So fuel is fine.


Car still kind of ran the same as on the video i linked previously, it had to adjust the fuel a bit because fixing the air leaks obviously changed the fuel mixture as well.

But just to be sure , i actually went back to the ignition side. In particular the spark. I noticed it was quite weak, it was visible but not blue. Spark was orange/yellow. Did a bunch i tests i found in haynes manual, and replaced ignition coil, because the resistance value was off. I used to have a NGK u1065, now i have a NGK u1078 (OE number 211 905 115 b). But that really didn't change anything. The weird thing is, even tho the spark is weak and not blue, it does run, although not perfect.

But during testing i noticed another problem. Probably the actual problem. Sometimes there is no spark at all, i crank the car, looking at the plug thats on the valve cover to check spark, but sometimes it skips a spark. I am explaining this terribly but here is a video: https://youtu.be/nOwGZG5e35I


IMPORTANT: this happens on all 4 spark plug cables, not just this one.
New spark plugs didn't help.
And yes i did alrealy replace rotor (1Kohm bosch), distributor cap, ignition leads, and distributor as well. The only thing in the entire ignition system that i didn't replace is the transistorized ignition unit, but i honestly have no idea if that thing could cause this kind of failure.
I also checked the sparked directly at the coil, bypassing the entire distributor by just attaching an ignition lead with a spark plug directly at the coil. Video here: https://youtube.com/shorts/hXdOIpVS7tI?feature=share


Did some multimeter testing. Coil has 5,5v on it from 15 (+) on coil to ground on battery. During starting that is 7,3v. So it does get a starting boost. Basicly all the other test i found in haynes where also within spec...


For info, my car is 1981 eu model, with transistorized ignition unit and resistance wires(Not the ballast resistors), and the spark disappearing has nothing to do with it not showing up on camera or something, i saw it with my own eyes as well.


So anyways i really hope someone has any idea what could cause this and what i should focus on first. Its sometimes just really confuzing to me since this is my first project car, but i am determined to get it back up and running.

[morghen]

Very interesting!
I had an ignition unit fail on me once on my old 924NA, but if i recall correctly my car just didnt start anymore.
A friend that now has my old 931 was chasing a somewhat similar issue like yours..he had a sort of a missfire at certain RPM.
So it very well could be that your igniton module is acting up.
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https://www.the924.com

[RVA]

yes that could defenitly be the problem. but Its definitly a really strange problem.