Rebuilt DME, It Still Dies!
 

:mad:I seem to have a problem that is not going away. First I put on a new coil (Bosch Silver), new DME relay, new distributer cap and bug, and new spark plugs. I also replaced the speed and reference sensors. Test drove the car and it still had a intermittent miss. I then sent the DME to Specialized ECU Repair ( I was told it had some cracked solder joints). Put the DME back in the car and it started and ran for about 30 seconds and died. The car will restart but dies pretty quick again. What could this be now? Bad coil? I am out of ideas. I am throwing money at this thing over and over to fix my problem, but it will not go away.

Talk to Ingo Schmitz, he has a good trouble shooting regimen.

When mine didn't fire it ended up being a bad fuse for the supplied 12v power.

Mine did the same and I am not done diagnosing but I think it was the relay. seems fine now. You can jumper the relay to eliminate that as a problem short term. Dont leave the jumper in long term it will drain the battery. Lots of folks have had brand new relays go bad.

Is this a 3.2 car?

Yes, A 1985 RoW Carrera. I still have my old relay also. How do I jumper the relay?

Dme
 

He is the guy
Good luck,

Gerry

I'd be sure to have a really close look at the female side of the DME relay connector. Make sure those pin receptacles look ok,..ask me how I know.

Best,

Doyle

+ 1 for Ingo, he is great and helped me with this.

To Jumper the relay remove the relay and look carefully at it. There is numbers associated with each pin.

Locate the #30 pin, the #87b pin and the #87 pin.

Now you have to identify the corresponding holes on the relays plug on the chassis wiring harness under the seat.

I used alligator clips with wires to join 30 to 87b and 30 to 87 on the plug.

30 is 12 volts and 87b and 87 are fuel pump and ignition.

Thats it. Try to start the car and see how it goes. Remember if you leave it jumpered the battery will drain. I think the fuel pump runs?

Good luck.

Did any of the plugs look really sooty?

fuel pump pressure test

absolutely- fuel pressure test for sure and replace all filters before doing so as well as check strainer in tank.

I did e-mail Ingo, he directed me to check the speed sensor. I had forgotten to tell him in my e-mail that I had already changed both speed and reference sensors. He also told me that it could be the ignition switch. I ordered the switch today from our host. I plan on checking fuel pressure. I also have a new fuel filter that I tried to change but a PO tightened the bottom nut so tight that I need a line wrench to loosen. Thanks for the input guys!!!

A simple way to check speed/reference sensors is to disconnect them and measure the ohms - it should not be zero or infinite. And while the test meter is connected, use a heat gun to warm them up. In my experience this is the most common failure pattern for this kind of sensor.

Also it's worth saying just because they are new doesn't mean you don't have to check them.

This problem sounds like classic cracked solder joint on the coil transistor, but the symptoms also mirror a sensor that goes bad as it warms up so you need to check them.

Are you getting spark when it dies? I think you need to be sure it's a no-spark condition and not a fuel starvation. Ignition/DME problem will cut the engine very fast, fuel starvation will kinda run rough and then die in my experience.

Chuck.H
'89 TurboLookTarga, 365k miles

When the car dies it will restart just fine, then dies again. It stops running instantly, no sputter or cough it just quits. I do not think it is a fuel issue but I will test fuel pressure also. I had a voltage regulator overcharge episode just before all this problem started, I am wondering if that had something to do with it. Thanks everyone. Just where exactly is the coil transistor?

Open the DME and separate the analog and digital circuit boards (keep yourself grounded, you don't want to build up static. You can do this by touching metal).

Hold the DME in front of you with the connector facing you. The coil transistor is on the right, standing up on the metal heat sink off the board. it's a metal can about the size of 5 nickels stacked together, labeled something like 1012. Check where those pins conencted to the transistor go thru the circuit board (you'll have to remove the bottom plate to see them). If in doubt, reflow them with a solder iron.

Chuck.H
'89 TurboLookTarga, 365k miles

The coil transistor

Bad AFM? If the carbon track wears out in the AFM it will behave just as you described. Will catch on startup and then die.

Test the output voltage of the AFM signal line with key in RUN engine stopped. Then slowly push the barn door inside the AFM open with eraser end of a pencil and monitor the output voltage as you swing the door open. The voltage MUST sweep cleanly from about 0.7 to 4.8 vdc.

My 84 3.2 had a start and die problem a while back.... it turned out to be a fuel regulator and fuel dampener problem. I replaced both of those and the problem was solved.
A fuel pressure test should tell you if that's your problem.

Stop replacing parts. Start testing components.

- Get a cheap used oscilloscope. This one is in Tulsa http://tulsa.craigslist.org/ele/4096219792.html but you can find cheaper on ebay. Don't be intimidated by all the knobs. The manual will get you going immediately and you will have fun testing the flywheel sensor signals.
- Get a fuel pressure gauge and hook it to the pressure test port on the rear of the drivers side fuel rail.

All of this stuff is testable so stop spending more for the unneeded parts and you will end up with a permanent collection of diagnostic tools and a greater understanding of the car.

I had similar (though not exactly the same) symptoms due to a poorly-connected CHT sensor. I presume that a failed or failiing sensor might be a contributor.

Test info in this thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/562175-black-smoke-exhaust.html#post5541332

If I open the DME it voids my warranty. I don't want that. I am going to contact ECU doctors about the coil transistor.

I did some testing per Bentley manual and ECU Doctors. Using a fused jumper between terminal 30 and 87B on the DME relay plug-in with a on/off switch I was able to test fuel pump. It works fine. But using terminal 20 on the DME plug-in per ECU Doctors, the fuel pump did not work. This method goes thru the DME relay, I think my new relay is bad. What do the wizards at Pelican forum think about my findings?