Challenging problem! As I have been following the thread, it occurred to me that maybe the DME failed at the moment you turned off the engine after that 30-second test run. You mention there are a lot of loose wires in the engine area. Is it possible that there is some mis-connection or missing connection that allowed the battery/system voltage to become un-regulated ? Perhaps it pushed up too high and damaged the DME or at the instant of shut-down a voltage spike occurred that took it out? Seems like the only reason you have no spark would be bad crank sensor or a dead DME.

Part of the problem is not knowing what problems would cause the DME to not send a pulse trigger signal to the coil.

If something were wrong with injectors, would that cause the DME to not send the pulse? Which other engine sensors would cause the DME to not fire the coil if something were wrong with them?

Mysteries.... I am going to try and see if I can find someone local with a 3.2 that I could swap my DME into and see if it runs.

Well if you can get a working DME and test it in you car it would be good but the odds that you will find someone to lend you one are slim.

Bad injectors would not cause a non start problem.

While some of the items you tested are ok statically, they might not be under power. The fact that it start up once it might be a clue that something fried under power.

Before you take it to a $100+/hour shop, I would get new; DME Relay, Coil, Coil wire, Distributor Cap & Rotor. If it still a no start, well you tune up is done and you get spare part for the next time you'll need to isolate a fault.

Put an '85 3.2 in my '73 911 then ran it for several months. Pulled it out and put it in my son's '71 and no start. Bought and replaced all the sensors, no start.
Started checking all the ground wires on the wiring harness and found one broken. Old copper is brittle. Fixed it and engine fired immediately and hasn't failed to start for 8 years running.
If all your feed wires are OK check your ground wires, they are there for a purpose.
Good luck, I was ready to blame Gremlins.

check this parallel thread - some excellent links in embedded answers

http://forums.pelicanparts.com/porsche-911-technical-forum/767428-84-carrera-no-start-questions.html

http://forums.pelicanparts.com/porsche-911-technical-forum/738792-3-2-starts-dies-immediately-all-tests-good.html
.

Ok... some progress. I called up an old racing buddy who has a 3.2 track car. Drove down to his house with my DME. Plugged it into his car. Nothing - would not start. Plugged his DME back in - fired right up.

Bad DME.

So - Where is the best place to source a new one or ship mine out for repairs??? I am in Atlanta.

Since you already open the DME and look for cold solder joint problem, one more swap before sending it for repair... DME chip.

That should be easier to find as everybody that upgraded to a performance one (like SW one) still has their original.

eBay - several rebuilders advertise there - about $750 with your core

I haven't dealt with either of these companies, but here are two Pelicans that contribute information to the Forum.

Systems Consulting - Products

911Chips.com - Porsche Motronic ECU / DME Repair

No pressure - but the Petit Le Mans countdown has begun - Petit Le Mans

Mike

Right here at PP, $450 and 2 years warranty; Pelican Parts - Product Information: DME-REBUILD

TOTAL NIGHTMARE GRRRRRRRRRRRRRRRRRRRRRRRRRRRR

So I shipped my DME off for repair, and a fellow P-Car nut who had an extra offered to let me borrow his to get the car running and driving until mine came back. So installed the DME he lent me and the car fired right up and ran great.

I take it down off the jack stands, get the drivers seat bolted back in and go for a test drive. Car runs great! Awesome!

I pull back into the driveway, shut her down and come back out about 30 minutes later to go get some gas.

No start. Exactly like before.

I am going to again remove the DME and see about heading to my buddies house to test it in his car again, but it appears that there is something wrong in this car that intermittently causes it to fry the DME.

So every time you want to test a possible fix - if you have it wrong, it costs you $450.

What could possibly cause damage to the DME?

Any ideas or suggestions are greatly appreciated.


Terry

Not sure if anyone is following this thread any more or not.... it does seem a lost cause.

I took this second DME down to my friends house to give it a try in his 3.2. Surprisingly enough - his car fired right up with it. It did not seem to idle all that well... but it certainly fired up. In my car it does not start and gives zero indication of starting.

Utterly baffled at this point. Steve Wong has my old DME and is digging into it, hopefully what he finds wrong can help point me toward whatever is wrong.

A bad alternator putting out too much power will fry the brain..
Bruce

I know you check it, but did you ever change the DME relay?

3.2 test stand
 

Terry- If you don't get this solved and cold weather sets in-consider building a test stand and setting up your engine DME coil fuel pump etc on it. I know that is a lot of backtracking-but it may be worth it. Then you will have full access to check output of all the sensors, and to the DME pins. Here is a photo of a test stand I made out of angle iron for my 3.2-it allowed me to fix a couple of issues before the install. I used a starter ring adaptor, and made a small fuel tank.http://forums.pelicanparts.com/uploa...1378467433.jpg

I would start by confirming the wiring for the ECM.

Disconnect battery and ECM.

Take a ohm meter and connect 1 lead to each pin of the 35 pin connector of the ECM plug. (Pin 1 is the coil)

Disconnect the wire from the device at the other end (coil) and put the other lead at the other end of the harness. (disconnect coil wire and connect to meter)

Make sure that you have ~zero ohms through the harness, and that all the other 34 pins on the ECM connector have infinite ohms to confirm no shorts through harness.

Move on to pin 2. (idle speed switch).

Mike

Verify the alternator, regulator, battery are putting out correct voltage. I would say to make sure every ground is clean and solidly connected. Transmission ground strap, terminations on intake runner, rear electrical console ground strap, alternator ground strap, all the pins in the 14 pin connectors and the connector to the injectors. Check with 12v to injectors to verify each one clicks open and none are shorted or sticking.

I can think of something that may cause these symptoms - if the reference or speed sensors are too far from the flywheel, they will give a weak signal. I could see this weak signal 'sometimes' being read and sometimes not, and I could see some DME's being able to trigger on the signal, and some not. Maybe the ref sensor holder is loose? Just something to check, I haven't reviewed all the posts to see if this has been done. I always try to get sensors like this as close as possible to their trigger wheels.

HTH,
Chuck.H
'89 TurboLookTarga, 362k miles

Another DME relay nightmare! Almost like post 54

Steve Wong has my original DME for repair.... says it is toast, the primary chip is fried, caused apparently by attempts to make the signal from the DME work with a '73 model tach. The tach has never worked since I owned the car but I know the prior owner attempted to wire the stock '73 tach to the DME tach wiring without success.

None of this makes any sense at all to me. The car DID NOT stop running... it refused to start again after being shut down. The problem has never been the car dying while running but always refusing to start - even if it did start only moments before. If something was fried in the DME, would the car not have stopped running the instant the frying occurred???

I tried replacing the relay - no change, still will not start.

I have tested and checked pretty much everything there is to test or check on the car. It simply will not start.

At this point, I am seeking some Porsche technical GOD to try and take the car too for repair - OR - planning to tear it all apart again and launch into the process of replacing this Motronic CRAP with carbs and a sane ignition system.