924Board.org

[Michael2200]

Hiya folks,

Got a 924 that was recently at the mechanics, getting some work done. This included a cleaning of the injectors and new injector gaskets. The car ran great for a few days, but then one day I heard a whining from the rear sporadically, which I thought may be a dying fuel pump?

The noise went away, but a day or two later, the car began to feel sluggish at higher RPM/under hard acceleration, as well as it started to sound like it was misfiring/sputtering(?). The problem seemed to get worse, happening more and more often under lower and lower RPM. Start-ups and idles were completely fine, though.

I pulled the plugs and they seemed a little wet, but not bad at all, so I got a new distributor cap, rotor, and plug wires. Having swapped those out, the car is now running terribly (won't rev up over 1/2000), etc. I have made sure the wires are in the correct order, and the distributor cap should be in the same place the old one was.

The external fuel pump was hooked up by a PO to run when the key is in the 2nd position, so I know the car is getting fuel (as the fuel pump can be heard), and considering the fuel lines are new and tank was cleaned. Could it be that my in-tank pump died? I still don't think this would explain the issue, though, seeing as it shouldn't even need the in-tank pump to run. I sadly don't have a pressure gauge to test the CIS system, yet.

Here's a video of a rough idle: https://imgur.com/a/yEnhwas

I decided to test my ignition coil resistance, but whilst unbolting it, the plastic around one of the terminals snapped off, so as a first step, anyone know what a suitable replacement is? Would this one work https://www.burtonpower.com/bosch-blue-high-performance-non-ballasted-ignition-coil-12v-0221119027.html? The NGK 48302 seems out of stock everywhere.

Anyone have ideas what my issue could be? I'm thinking it might just be a bad coil, but would love some input.

[Beartooth]

You should hear kind of a whining sound from the fuel pump - loud enough to be heard sitting in the car with the engine off, but not once it's running unless you go back there. If the pump got noticeably louder, I'd be looking in that direction - and it could be the pump (main or in-tank), or it could be some kind of blockage. If it is a bad fuel pump, it'd be obvious if you could hook up a fuel pressure gauge - running that badly, I can't imagine fuel pressure is anywhere near what it should be. Sometimes the tricky thing with a failing fuel pump is it can get enough pressure with no fuel demand, but can't maintain pressure and causes power loss or rough running when you put your foot down. I can't think of one I've had do that - they've either seized or had to be replaced because of leakage. My in-tank pump was long dead when I got my car - along with the main fuel pump - so I just eliminated it and put a sock filter in its place (or for a little more money, you can use the 944 fuel strainer). It could be the in-tank pump failing and causing a restriction, but I don't know if that's likely to happen if it fails. You should be able to test that by either powering it directly, or disconnecting the main fuel pump, turning the key on, and seeing if you hear and sound from it.

On the ignition, that doesn't seem like the primary issue to me. Obviously, it shouldn't have made things worse to replace some things - maybe something on it's last legs failed when it was disturbed. Can you confirm that you didn't move the distributor? Maybe the coil got damaged while you were replacing things - also double check connections and such. I think the coil is a pretty common type: I replaced mine with an MSD blaster 2, and it's worked fine for around 5000 miles. The spec for primary resistance is 1 to 1.3 ohms, and I doubt you can hurt anything if you're in that range. The MSD coil I've got is actually 0.7, so going a little lower won't hurt anything, at least in the short run. I'll not say you could drop in any old coil that'll fit in it, but I'd bet most universal cylindrical coils would work here.
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1980 931 diamond in the rough

[Michael2200]

[Beartooth]

I only mention the distributor because if the nut for the hold-down plate wasn't tight enough, it might have moved a bit and thrown the timing off. If the nut is loose the distributor will rotate freely, it doesn't set into one particular position. Checking the timing would be a good idea, but probably not necessary if the distributor is tight. Air leaks could definitely be a problem. Any cracks in the hoses or boots after the air flow plate would cause issues - most likely leaning out, high or low idle, etc. Visual inspection might find them, or if you can keep it running, spraying brake cleaner or starting fluid (definitely work in small sections and give it time to evaporate if you use that) sprayed on the rubber pieces and interfaces might help find them. The best method is a smoke machine that pumps smoke into the intake, which should reveal any leaks. Another tell-tale sign is if you can get the engine to idle smoothly by pushing up on the air flow plate, although that might also compensate for low fuel pressure. Anyway, hope this helps - it's a learning process, and there'll always be some trial and error.
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1980 931 diamond in the rough

[morghen]

Runs on 2-3 cyl.
Swap back the parts that were on the car when it ran fine.
You may have a bad ignition lead.

A new coil may also be a good idea.

If you dont find the problem and/or want an update on the engine management system, have a look on my website. I make bolt on EFI kits for these cars, tune included and the kit does not invalidate the historic vehicle status as there are several historical 924s in Germany with this kit.

[Michael2200]

Replaced the coil and checked the spark leads again, and the car sounded a lot better for the 5-10 seconds it ran, before dying.

Sounds like it's getting spark when cranking, but now it won't start. Fuel pumps aren't really heard, so I'm thinking either a bad connection or dead external pump. Interesting the car lit of at all on the first go - must be that it kept pressure in the accumulator or had just enough feed from the internal pump.

Will update in a day or 2!

[Michael2200]

Fuel pump runs, gives pressure.

When the pump is on, I hear some sort of hissing/whistling from the fuel distributor unit, and popping of the airbox showed a little bit of oil at the bottom of the air metering plate.

Did what you shouldn't do, and with the pump running, but not cranking the engine over, pushed the air metering plate up a little bit a time or two. Result was that each of the two times I did that, the car fired up, then died a second later.

Sooo I'm guessing bad fuel distributor not sending [enough] pressure to the injectors? They were cleaned and resealed by my mechanic a few weeks ago (trying previously to hunt down a long crank to start issue), and car ran fine after that, so I'm guessing its not the injectors.

[Michael2200]

Update, in case anyone in the future stumbles upon this thread. Problems aren't resolved, but I checked the external fuel voltage across terminals, and am only getting about 7.5v, which is obviously also not ideal. Going to check and see if it's a grounding issue or something else tomorrow. Seems like potentially several problems at once?

[Beartooth]

Could definitely be multiple problems. I'd focus on electrical and fuel supply first: maybe it's barely getting enough voltage to run the pump. Don't expect full battery voltage, but 7.5v is too low. With the fuel pumps running, you should hear a low-pitched hissing sound from the FD, caused by flow through the fuel pressure regulator, I think. On a healthy system, when you deflect the air flow plate with the pumps running, you'll hear a "wheeeeee" sound. The injectors make that noise when they're delivering fuel. You don't want to do that very long, you'll wash down the cylinders and eventually hydralock a cylinder; I'll play with it a few seconds, then crank it over to make sure I don't build up fuel. The inner workings of the air flow box usually look oily: it's from gas that seeps past the control piston and evaporates. The best backyard way to check the fuel distributor is to disconnect all four injectors, put the injector lines into little jars of some kind, and then run the pumps. There should be virtually no output to the injectors with the air flow plate at rest. A drop every ten seconds or so might be acceptable. If that's ok, deflect the plate 1/4 to 1/2 its travel. You should get flow out all four ports. Run the jars up to halfway full or so and measure each. If they're within 10% or so, the FD is probably fine.
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1980 931 diamond in the rough

[morghen]

Check that the rubber hoses between the kjet and the theottle body are connected and intact.
But if your mechanic opened and messed with the fuel distributor and/or wur, there is a fairly large chance that is the problem.
They are rather difficult to rebuild successfuly.
Many have tried and failed, leaving them with a broken kjet.

If you decide to give up on trying to revive the kjet and want a running car, well you know what to do.

[Michael2200]

[Michael2200]