Hate to be that guy but another "no-start"

[Cappt]

I bought another 944 with a problem.
The issue is no fuel pump operation with the DME relay installed. Also no fuel pump operation with DME jumpered from 30-87/87b.
The strange thing is when DME is jumped from 86-87/87b it runs perfect.

What is stopping the fuel pump from operating with good power (12+) volts on pin 30 to 87/87b????

DME computer has been swapped, no change.
DME relay changed.
Ignition switch has been replaced.
Ref sensors have been replaced.
Ref sensors ohm'ed out to DME computer plug- 850 & 869
Ref sensors installedcorrect-DG to pin 8/27
Fuse panel was swapped with another-no change.
No factory alarm model.
Has aftermarket alarm with relay on starter solenoid wire -working.
Engine Block and bell house grounds cleaned.
Battery Neg cable replaced.

With DME installed=no tach bounce=no start.
With DME jumped 30-87/87b=no tach bounce=no start.
With DME jumped 86-87/87b=tach bounce and good start.

Thanks in advance for any helpful suggestions.

[Tom944]

I would check for 12v on pin 30 of the DME relay socket. Looking at the schematic it should be battery positive. If not the DME relay will not work.

[Cappt]

Just some closer because I hate these "problem threads" that just end with no solution!!

First I found the speed ref sensors voltage too low @ <1V when cranking on pin 8-27.
Re-set the ref sensors to .84mm, cranking voltage now good @ 2.7V on 8-27 and .4V on
25-26.
Car still wouldn't start.
Checking cranking voltage on DME harness pin 4 it looked low @10.8V
Found battery-starter cable in poor shape with cracks and corrosion.
Replaced cable with much better one from donor car, cleaned up connections.
Cranking Voltage at pin 4 still looked low, 10.8V. No-start.
Replaced what was a new battery (5/19) from WM.
Cranking voltage on pin 4 now showed 11.8V.
Re-connected DME computer and car fires right up, runs fine.
Next day car still starting and running good.
On to smaller issues!

[jjeffries]

Cars managed by computers are very sensitive to having a good battery. Glad that you're fixed. John

[pfarah]

Good to hear!

[Cappt]

I might have spoke too soon. Twice now the car wouldn't start, no tach bounce.
If I disconnect the battery pos. And then disconnect the DME, reconnect the DME and then the battery pos it will start and run fine.
I have another DME from a different 87NA that wasn't running when I got it. This DME does the exact same thing?

I opened up one DME and it looks kinda nasty?
What do you think? The brown funk brushes off with a toothbrush.

[DannoXYZ]

Surface corrosion won't cause issue because you still have solid connection internally.

Common issue is corrosion on contacts of DME connector. That corrosion gets in between terminals of connector and terminals on DME box. There are de-ox sprays you can get that will dissolve corrosion on those. In process of disconnecting and re-connecting DME, you may scrape some of this corrosion off and get better connection... temporarily.

Another common issue is fingers of DME connector female terminals spread apart over time and no longer makes reliable constant contact with mating male connector on DME. Measure gap-width of every single female terminal on DME connector. If it's over 1mm, you won'd get reliable connection. Easy enough to replace individual terminals. Search for my "DIY harness connectors" thread with part# for replacement terminals from Mouser. Heck, you can even build brand-new harness from scratch if needed.

[Cappt]

Cool, will take a good look at them with a magnifying glass when I get back home.

[Bukowski]

intriguing

I assume the starter is turning the flywheel like it's supposed to

how about :

- cleaning the injectors
- flushing out old fuel with fresh fuel
- could this be a case of bad out-of-the-box DME relay

[Cappt]

Originally Posted by Bukowski

intriguing

I assume the starter is turning the flywheel like it's supposed to

how about :

- cleaning the injectors
- flushing out old fuel with fresh fuel
- could this be a case of bad out-of-the-box DME relay

I have two new relays, no difference.
Relay jumper- runs great off 86/87/87b
Relay jumper- will not run off 30/87/87b
When the tach bounces it starts and runs great. If you shut it off it might not start again because no tach bounce.

When I get home Sun I'm going to inspect the DME harness plug. I also have some other ref sensors out of another car, it may be bad sensors even though their new FAE types.

I ohmed out the temperature sensor and it also checked good.

[Cappt]

Started good yesterday and this morning, this afternoon it wouldn't start, no tach bounce and I can't hear the Focus 9 DME relay prime up the fuel pump?
Inspected the DME harness and it looks OK, I slipped a bayonet into each slot and the couple that felt not as tight I bent closed with a small scribe. Cleaned both sides with electronics cleaner and toothbrush.

[DannoXYZ]

Are you measuring speed/ref sensors at DME plug in cabin or out at sensor connectors themselves?

Connectors and wiring for sensors are often cracked and broken in cases like this. When no tach bounce, try pressing sensor connectors together and wiggle wiring going into them slightly.

You can make replacement harness for speed/ref sensors to DME for about $10.

[Cappt]

Does the DME receive or send any signal to the ref sensors before the ignition is turned to the crank position?
I ask because after close inspection with a mag glass I noticed the DG connector on the harness side had a couple folded fingers and the bayonet side was also showing some damage? I was able to straighten them out enough for now to get a proper connection. The car did start after this. I did however also inspect the battery +pos harness at the battery side. It looks very OLD and stiff there. I tried to move it around some, not sure now if maybe this is the culprit, wish I hadn't done that. I need a smoking gun fix or won't trust the car enough to shut it off.

[DannoXYZ]

Nope, speed/ref sensors are passive and DME only receives their low-level signals.

Battery-cables another possibility. Measure voltage at DME-connector, especially while cranking. Voltage at battery may be OK, but if DME doesn't receive enough, it won't function. Bad battery-cables could also be culprit here.

[Cappt]

Originally Posted by DannoXYZ

Nope, speed/ref sensors are passive and DME only receives their low-level signals.

Battery-cables another possibility. Measure voltage at DME-connector, especially while cranking. Voltage at battery may be OK, but if DME doesn't receive enough, it won't function. Bad battery-cables could also be culprit here.

OK, yeah that's what I thought with the ref sensors, they only send data (voltage) when the engine is cranking.
I have 10.3V at pin 4 while cranking, I believe this in the normal range.

The problem is before the cranking part though. I can tell it's not going to start and will see no tach bounce when the fuel pump doesn't prime up on the first ignition click.
When that happens I test for Voltage and ground at 85/86 under the dme relay and it's good. 30 also shows 12V so no reason for the DME not complete the circuit unless it's getting bad data from one of the other sensors and not allowing completion.

Today I swapped out the AFM with another. Funny thing though it started even when I had forgot to plug it in.

I've tested the ref sensors at the DME plug pins, checked good.
I've also tested for ground on pin 2 with throttle closed.
The temp sensor plug under the intake doesnt look so great, would a bad temp sensor stop the DME from starting the car?
I'm using this chart from specialized ECU.
Porsche 944 DME Diagnostic Flowchart - DocShare.tips

Thanks for your help, I'm running out of ideas other then an entire new DME harness.

[DannoXYZ]

Yeah, DME just dumps fuel & spark blindly to start, and then checks for AFM voltage. If it doesn’t see airflow after about a sec after starting, it turns off engine.

Bad ECT will definitely prevent starting. Measure resistance at room-temp and boiling to compare to values listed in workshop manual.

Search for “DME test plan” for troubleshooting flowchart (ignore KLR tests). Follow steps in order and some part of that flowchart will pinpoint your exact problem.

[Cappt]

I may have found the smoking gun here.
When the car is idling and I grab this cable and move it around the car dies immediately?
The red/green was burned inside for about a 14". I believe it got wet and was probably shorted.

[Cappt]

I will cut them all back to here and splice in new up to the battery.

[DannoXYZ]

Those are not factory wires at all!

Where do they start and where to they end?

I'd remove ALL of them.

[Cappt]

Originally Posted by DannoXYZ

Those are not factory wires at all!

Where do they start and where to they end?

I'd remove ALL of them.

They look just like the ones on my parts car (which are not great either?)
They run from the battery positive post into the big black harness that runs along the top of the rear engine firewall to the relay box.