DME outputs help
 

Driving down the road the other day my ‘85 911 sounded as though something gave up under pressure and had a decent backfire. Everything turned off right then and I couldn’t get it restarted. I had just replaced the DME Relay and both crank sensors. Now, I don’t have any injector or ignition pulse output. I have all the inputs needed to run, but no outputs. Next step? Send DME for repair?

Regarding the "turn off" and "not starting" and nothing else you noted, I suggest checking the white connector on the driver's side of the engine towards the front. It's just above the fuel rail. It's the cylinder head temp sensor connection. Below it are 2 other connectors---speed and reference. If that white connector comes loose, the engine will quit and won't start. Very simple to check this and either it solves the problem or is one thing checked off the list.
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You good with a soldering iron? You might try looking for bad solder joints yourself before sending your dme in.

Are you sure you have power to the DME relay ?
Ant.

when you say "Everything turned off right then", what do you mean when referring to "EVERYTHING"? engine, lights, instruments, radio...

Hey all. Thanks for replying. When I say everything I mean all engine components. There was still battery power, but the engine just quit. I could still turn the key and hear the fuel pump and try to turn the engine over, but seemed as though there wasn’t any spark.

Checked the temp sensor since I have just replaced the other two crank sensors the day before. I had it towed to a shop since I was frustrated after working on getting it started for months before and was successful, only for something different to jump in and shut the engine off. I was checking the spark plug wires and noticed that #2 seemed to have come loose and so maybe messed up the initial inputs? The shop got back to me and said everything with the “inputs” to the DME were working fine. Trouble wasn’t the sensors or relay. The “outputs” from the DME aren’t sending. No injector or ignition pulse outputs.

I’m terrible with soldering so I have decided to send my DME into @ischmitz here from the forum for a bench test and possible repair/rebuild. The local shop seems confident nothing else is wrong with the car. We will find out once the DME is back I guess. Not sure where else to look.

Sounds like a good move. Hopefully you can get back on the road soon!

What happened here after post #48?
https://forums.pelicanparts.com/porsche-911-technical-forum/1177269-85-carrera-no-start-help-3.html

Maybe should have continued with the first thread [as Dave pointed out] seems related to your original issue, anyway, good luck getting it sorted, I think [from the symptoms you've described] having your ECU checked out was the correct way to go.
Ant.

I was able to replace both crank sensors. Once those were swapped the car started right up. I then took the car for a drive the following morning and after about 20 minutes I made a right turn and rolled on to the gas and the car backfired and the engine quit. Couldn’t get it started again. Checked the crank sensors (visually just to make sure they were seated still) and spark plug wires since I had replaced those during this whole process. Everything seemed ok and nothing was/is leaking from the car. Towed to a local shop and they reported that the DME wasn’t sending any outputs. Sent the DME to Ingo and the DME apparently checks out as totally fine. No issues. Now I’m at a total loss for what the problem is.

Since the shop said the DME sends no outputs (spark and fuel pulses) and Ingo said the DME is OK, that leaves it to the crank sensors. These are about the only inputs (ref and speed) that would yield no spark and no fuel outputs if the DME doesn't receive them properly.
Since you just replaced both sensors, you should check their proper connection. Make sure connectors are fully seated. Test their resistance at Motronic connector and their AC voltage while cranking. Your shop should know how to do this.

Check the wiring harness between the dme and the engine. Where did the shop make it's measurements? I had a bad wire in my harness that caused the engine not to run. Looked like a dme problem. You can do continuity checks between the 35 pin connector and the respective end points on the engine.

The other possibility is the pin in the flywheel has been damaged, or knocked out, this would mean no pulse from the crank sensors, this could have happened from not setting the gap properly when the new crank sensors were fitted possibly ??? :confused:
Ant.

Bump,
Any update on this ?:confused:
Ant.

You missing a Motronic/DME thread, Ant? :) :D

:D
Just curious!
Ant.

Easiest way to see if you're still getting signals from the sensors is to take an LED and plug it into the ref sensor pins and one in the speed sensor pins on the DME harness plug. If the LEDs pulse as you crank the engine, you're still getting a signal. Other option is to check with an oscilloscope.

There is an LED test light that plugs into the fuel injector connector for this purpose. Auto parts stores sell them.

I think Josh was talking about checking the signal directly from the speed and reference sensors themselves, while cranking the engine, not looking for the signal to the injectors from the DME/ECU itself, if there is no signal directly from the sensors themselves, then there will be no signal to the injectors, or the ignition coil, hope this makes sense.
Ant.

Here are some of the photos the shop sent me as they have worked on figuring out the issue. A few of you have said to measure while cranking and I’ve passed on this info to the shop. Gave them back the perfectly good DME Wednesday night and he was going to get back to working on my car on Monday. Hopefully I know more soon. If not, I’ll be looking to trailer it to another shop.
http://forums.pelicanparts.com/uploa...1754690437.jpg
http://forums.pelicanparts.com/uploa...1754690437.jpg
http://forums.pelicanparts.com/uploa...1754690437.jpg
http://forums.pelicanparts.com/uploa...1754690437.pnghttp://forums.pelicanparts.com/uploa...1754690571.jpg