mojorizing

Who are you sending the DME to for repair?
If you attribute the failure of the DME from washing the car, how can you be sure that re-installing the repaired DME won't be damaged again?

John McM

Did you replace the DME with a known good one to confirm the diagnosis?

Nolift914

Wow, I had a very similar situation. After buying my 89 c4 and having driven it twice i decided to bring it to the car wash. I stepped out to allow the attendant to pull it into the car wash and shortly after the attendant sat in the c4 the car died. The c4 didn't get a drop of water on it . After several attempts to start the c4 , it cranked but wouldn't fire up. I sent the c4 thru the car wash and tried again with no luck.

I had the car towed home, during the next several months, I checked the computer, dme and every thing else i could think of with no success. Finally with the help of my brother at Independent Porsche tech for 30 years we decided to go thru every connection on the wiring harness starting with the computer connector, the alarm module etc. Eventually we got to the DME relay board, we discovered there was no ground on the connector to the DME relay. We then unscrewed the board the check the wiring underneath. We discovered a set of non factory wires running from the DME ground to under the dash.

A prior owner in the 90's wired a kill switch to a factory hazard switch which had been installed between the lighter and the fog lights .
The attendant had turned the switch to put the hazard lights on to run it thru the wash. One turn and the c4 fired right up ending 9 months of frustration

klokwerk

The shop uses ECU Doctors. I haven't read enough good or bad reviews to have my own opinion of that outfit. So, I'm relying on my shop to know best. As for knowing if the repaired DME won't get damaged again, that's a real fear of mine and I've shared it with the shop. I guess I'll feel better after finding out what is actually wrong with the DME. Need more information to solidify the concern.
As for the car wash causing this, I don't think that anymore. I suspect it was about to go and just chose that moment to do it.

I had asked the local PCA group that has 964s if I could give them my ECU to see it would start there car. No one would take the risk. Definitely won't loan me theirs to put in my car. So I am out in the cold there. But in troubleshooting the connections, sensors, etc using both a mutlimeter and oscilloscope I and the shop are certain that no signal is coming out of the DME. Signal from the AFM, the flywheel speed sensor and the engine temp sensor (all needed to start the car) were good signals and getting to the connector of the DME. Signal in but no signal out = something wrong in the DME. At least that was our conclusion.
Really wish someone in the local PCA would have helped out, but oh well.

This is the craziest thing I've heard in a while! I'll have to share this with the shop to make sure nothing like that was done. Thanks for the story!

I really appreciate all of the support guys. I've been trying to stay positive about this whole thing. This has been a royal pain in the ***. Hopefully this will be it and I'll have nothing but smooth driving after this!

Knock on wood!

mojorizing

Have you sent in the DME to the ECU doctors? If not, I have a Baum tool inline diagnostic break out box for the 964.

http://www.baumtools.com/pdf/Pin_Out_Boxes.pdf

I could loan it out to you. You have access to an O'scope?
If you have a buddy that has a 946 where you can get valid signals from a local working car and compare it with yours would be great or I can go through my DME connections to validate inputs/outputs.

Let me know.

klokwerk

mojorizing, just talked with the shop again to get an update. They haven't sent the DME out yet and while we were chatting I brought up Specialized ECU Repair.

That's where we're going to send it instead.

But thanks for the offer! I only wish I had mentioned this earlier now. Honestly, I've lost all energy in troubleshooting this myself. After trying to get it to fire for the last few months I've thrown in the towel.

That Baum breakout box looks a lot like the pile of wires I ended up making in order to test the pin outs of the harness if I wrapped them all up nice and neat! I should have taken pics of me testing. Wires everywhere!

klokwerk

Final update.

The car is running and I'll pick it up from the shop on Friday! European Autohaus in Spokane is where I’ve had this work done and Obie is my mechanic.

The DME was returned from Specialized ECU Repair and the igniter circuit was found to be faulty and repaired. When we got it back and installed it into the car the damn thing still wouldn't start. WTF?!

So Obie went back through the components related to getting the car started and everything seemed to check out. A call back to Specialized and the DME was shipped back to them to verify nothing was wrong and more importantly, they had a 964 that they could test the DME on.

While the DME was in the air, the shop went through the ignition parts again focusing on the parts that I'd recently replaced. Those were the crank position sensor, the ignition control modules, ignition coils and the distributor caps/rotors and wires.

After doing some real digging, Obie found that the crank position sensor that Pelican sold me and that some of us have used is definitely NOT the right part to use. It’s a 993 part that we’ve been told should work in 964s. Even have to swap the connector out for it to fit. They found that this sends the right signal to the DME, but not at the right amplitude. When you look at it in an oscilloscope, the reference signal is there, and the voltage looks right, but the signal is ignored by the DME and so it doesn’t send a pulse out to the ignition control modules. A genuine Porsche sensor was ordered from Germany.

The ignition control modules that I also got from Pelican were bad and don’t work for 964s. These were the Huco units. DO NOT BUY THESE. They're junk. Apparently the ignition circuit relies on the signal coming from the DME to be able to pull down the voltage in order to trip the coil. These Huco, piles of junk, draw the signal to ground. Which kills the signal coming from the DME and prevents the coil from firing. Even having one of these in place will kill the signal to the other good unit. New Bosch units were ordered.

The last thing Obie said to me about this was that I had the distributor caps in 180 degrees off. Brain fart on my part. Thought I felt them click when installing them. Glad the thing didn’t fire when I was working on it. Might have caused a problem!

Well, Specialized got the DME and re-inspected it then put it into their 964 which fired right up. They shipped it right back and wouldn’t you know it…..

After the new reference sensor was installed, and Bosch ignition control modules were installed AND the distributor caps were oriented correctly the f’n car fired right up. Smoked like hell and spit oil from sitting so long. Not to mention from all the cranking done without firing up.

After the smoke cleared, they performed an alignment (while the car was down I installed all new suspension bits) and Obie took it for a test drive.

I couldn’t be happier.

PS: when they were aligning the rear, Obie found that the right rear trailing arm was likely bent. He couldn’t get it 100% to spec. I’ve started another thread to discuss that. For now, I’m glad this is over. I’ve learned WAY more about this cars ignition system then I care for. Give me mechanical **** all day long. Electrical? Fugggetaboutit.

Thanks for hanging in there with me while I suffered through this. Now I can't wait to get out and drive!

dlpalumbo

Could the Huco control modules have killed the DME igniter circuit by putting too much load on it?

911Jetta

You guys have been through hell! So glad both cars are up and running now.
A couple years back I was chasing a "Christmas tree" problem... electrical issues can be very frustrating!

klokwerk

I bought the Huco ignition control modules after the initial failure. So don't think so..
They definitely didn't help the situation!

klokwerk

Thanks man! It certainly hasn't been a ton of fun. And I've missed out on a whole years worth of events and drives. If you know the PNW that window is only 5 months long. Bummed about that, but still very happy I'm up and running again!