alexg123

So I have this car, a car Porsche purists despise. its a 1982 924 with an 87 944 turbo motor but its procharged. I have been working my *** off on it, new headgasket, arp head studs, clutch master and slave as of today, coil, distributor cap and rotor, injectors rebuilt and flowmatched, idle control valve, etc. The car has a history of randomly losing spark so it was parked for ten years. I talked to the previous mechanic when it lost spark and he never changed the coil, I changed the coil, spark yay! no. I believe this car is haunted by serious electrical gremlins as the whole ecu was swapped over from the 944 turbo. Help! the car also will kill any battery in 2 days of it being connected, I don't mind disconnecting it I just don't want to get randomly standed. Save me porsche wizards. PS this is my first time ever posting to a form.

divil

Welcome!

How did you verify the spark issue? Do you know that it's only losing spark, or could the entire DME/KLR be dead? When you lose spark, does the tach needle bounce a little when cranking?

The battery issue is probably unrelated - you have a parasitic drain that you need to track down. Hook up a multimeter in current mode and start pulling fuses one at a time, and see which one causes the current to drop.

Northern_aqs

Persistent electric issues like this may be related to a 39 year old under hood wiring harness. I would be surprised if there weren’t cracked, shorted sections of wire causing this.

I’ve replaced the harness in my turbo with a new unit from Kroon and when I removed the old one, there were many more cracked sections I couldn’t see when it was installed in the car.

alexg123

if the DME was also dead it wouldn't supply fuel right, it's definitely getting fuel. and I pulled the plug cap and threw a plugin it to verify, then checked the coil with a test light. No power.

alexg123

how hard is this to do? seems pretty like a pretty advanced job as the most wiring I have done is a killswitch on a dirtbike. Seems like a last resort as couldn't simply be a bad ground?

Northern_aqs

The replacement was costly, but very simple. The Kroon harness is an exact copy of the factory harness down to wire colours and connectors. You simply unplug the old and plug in the new.

Your problem may be a ground issue, yes, but which ground?

alexg123

I'm seeing one on pelican parts for $158. how much did it cost you? and yeah I have no idea what ground. my bike spun a rod last Sunday and I don't know which to fix;(

Chapman951

Randomly losing spark sounds like a faulty DME. I would swap it out and see if that resolves the issue.

I would jiggle the injector harness while it’s running to see if that gets the car to turn off.

Tom M'Guinn

Welcome!

Procharged? Meaning it has a belt-driven supercharger? Does it still have the turbo? I think we need pictures!

I'd probably start by finding the parasitic drain that is causing the car to kill batteries in two days. Youtube has endless videos showing how to do that -- just search 'parasitic drain.' Constant problems like that are much easier to diagnose than intermittent ones, and hey you might get lucky and discover they are one and the same problem.

The harnesses on these cars are old and prime suspects for intermittent problems, but cracked solder joints in the DME are also fairly common, as well as in the KLR (if you have one, try bypassing it), and ignition switches can go bad, and alarms, etc., etc. but as you say some of that will kill fuel too. What happens to the tachometer when you lose spark? Does it drop to zero or keep showing the revs? Knowing that might help too.

Did this start before or after the engine swap?

Dwizle

Have you checked the gap for the Speed and reference sensors?

alexg123

new dme relay same problem, now I can't even get the car to start. If it was a bad wiring harness wouldn't a good bump on the road or something cause it to short? The problem only occurs after the car has been shut off.

alexg123

the previous mechanic replaced them, never solved the problem although I might replace them again just for ****s and giggles.

alexg123

I don't have premium rennslist so I cannot post photos. But yes it has a Paxton ProCharger, I plan on putting a k26/8 on it if I can figure out these damn electrical problems! I do not know how to bypass the DME or KLR, although I do have a new ignition switch somewhere so I will replace that when it stops raining. The tach does bounce with no spark when cranking. This was after the engine swap which I did not perform it was done in the early 2000s late 90s before I was born. I will look into the drain, also the car is overcharging like 16+ volts! I have a new voltage regulator but I have no idea where it is on the car so I can install it.

Thanks a lot guys! -Alex

944M3

I would start by cleaning all your grounds. Look up location for all them. The condition of your grounds will give you an overall indication of how corroded the rest of the wiring harnesses are. I had crude caked on most of my grounds. To resolve a mystery alternator issue, I had to replace the wiring harness from alternator to starter. It looked good to the naked eye but once I replace it alternator worked fine.

If that doesn't work, you might have to start looking at wiring from coil to ignition switch and down to ECU. As a few gave mentioned, wiring is old and brittle in these cars.

But I agree, it could also be a bad ECU. I had one delivering fuel but not spark. Troubleshooting electrical issues is the hardest thing in these cars, especially if its intermittent. Old crusty wires.

jerome951

Sounds like a tough problem. Here are my thoughts....
Doubtful it is the ignition switch or you'd lose power to all systems.
Tach bounce seems to indicate the DME is getting a signal from the reference sensor.
You won't be able to bypass the DME or KLR and get the car to run.
Where are you located? I think best approach would be to borrow a known good DME and KLR to see if that solves your issue.
I suggest you also carefully check the wiring from the DME to the coil for nicks. It could be shorting occasionally.

I'm fighting a similar issue where my car loses spark after driving hard on the track. Allow it to cool for a few minutes and fires back up. Driving on the road is fine. I've had the KLR and DME rebuilt and am just waiting for a chance to test it on track again. If that doesn't solve it, I'll replace the wiring harness as I've swapped out everything else in the car.

The voltage regulator is mounted on the back of the alternator, which is inboard and back of the driver's side headlight bucket (if left hand drive car). You'll think the car was built around the alternator, but you can wiggle it out the top after removing some intake tubing....