No injector pulse, bad DME?

[Bert87]

Hunting down a no start issue with an '88 3.2. Car fires briefly when starting fluid is sprayed in the intake. I am getting spark, fuel pressure, and 12v on the injector but no injector pulse. I have checked the speed sensor, reference sensor, cyl. head temp sensor, voltage supply, grounds, and everything is in spec. Also tried jumping DME relay (30 to 87 & 87b).

I am testing for injector pulse using a noid light, and have manually grounded the injector pins from the DME connector resulting in the injectors clicking and noid light flashing.

At this point I am thinking it must be something wrong with the DME itself. I have taken it out and am about to start taking measurements. Just wondering if anybody has any other insight into this issue.

[gomezoneill]

Flywheel sensors are the usual suspect. The resistance readings are insignificant they're almost always in spec even though the sensors are bad. Replace the sensors cheap enough.

[86 911 Targa]

Originally Posted by gomezoneill

Flywheel sensors are the usual suspect. The resistance readings are insignificant they're almost always in spec even though the sensors are bad. Replace the sensors cheap enough.

^^^^^
I agree.
Just went through this a while back.

Best,

Gerry

[mysocal911]

Originally Posted by Bert87

Hunting down a no start issue with an '88 3.2. Car fires briefly when starting fluid is sprayed in the intake. I am getting spark, fuel pressure, and 12v on the injector but no injector pulse. I have checked the speed sensor, reference sensor, cyl. head temp sensor, voltage supply, grounds, and everything is in spec. Also tried jumping DME relay (30 to 87 & 87b).

I am testing for injector pulse using a noid light, and have manually grounded the injector pins from the DME connector resulting in the injectors clicking and noid light flashing.

At this point I am thinking it must be something wrong with the DME itself. I have taken it out and am about to start taking measurements. Just wondering if anybody has any other insight into this issue.

Good troubleshooting:

1. You get a spark - then the sensors are O.K.
2. You have fuel pressure - DME relay & DME ECM output for FP O.K.
3. You checked voltage on injectors - injector power & wiring O.K.
4. You used starting fluid - engine runs, that leaves the injector driver in ECM

Check again for the injector pulse with the temp sensor disconnected, sometimes noid light isn't
bright enough with sensor connected.

Most likely injector driver output of ECM damaged by over-voltaging alternator.

[ischmitz]

Unfortunately, it sounds like you narrowed it down to the DME itself. It is providing the GND path to the injectors. And since you got spark the sensors are fine.

If you are convinced NOID light results are good and fuel pressure is good there isn't much more.

Did you do anything to the car in the recent past or did it just stop working w/o any prior incident?

Cheers,
Ingo

[Bert87]

Well I got it running.

I took apart the DME and it had definitely been repaired previously including the injector circuit. I do not have a microscope here so I was limited to a crappy magnifying glass thing which didn't reveal cracked joints. I resoldered the leads for the diode and transistors on the injector circuit anyways though as well as pins 14&15.

Put it back in, measured voltage on each injector plug, resistance on injectors, and cleaned the connections (all in spec). Sounded like it wanted to start.

Removed injectors and soaked them in fuel injector cleaner overnight. Placed them back in the rail and checked for spray. One was more of a stream than a spray so I submerged it in cleaner, activated it a few times and let it soak. Buttoned it back up and she started!

So I am thinking it was either the DME solder joints, or could the dirty/stuck injectors have been creating too much of a load? Then manually activating them on the DME connector while testing broke them loose enough for the circuit in the DME to operate correctly?

Thanks for the help guys! Especially ischmitz, read many of your posts concerning the DME in the past week!

BTW prior condition was the car sitting in the garage for the last 15 years, ran when parked.

[Irhmsd]

Based on the fact it was sitting 15 years, I am guessing the major culprit was the dirty/bad injectors.

[mysocal911]

Originally Posted by Bert87

Removed injectors and soaked them in fuel injector cleaner overnight. Placed them back in the rail and checked for spray. One was more of a stream than a spray so I submerged it in cleaner, activated it a few times and let it soak. Buttoned it back up and she started!

So I am thinking it was either the DME solder joints, or could the dirty/stuck injectors have been creating too much of a load? Then manually activating them on the DME connector while testing broke them loose enough for the circuit in the DME to operate correctly?

Most likely it was stuck injectors, i.e. a common problem when an engine sets for a long time,
and not a bad DME ECM. You could have verified that the DME ECM was not the problem
by following the suggestion up-thread of removing the temp sensor to provide a longer
injector pulse width thus having a brighter noid light while cranking.

In any case, you saved not having to send it out for testing or worst case having it rebuilt when
it wasn't necessary.

[mysocal911]

Originally Posted by Irhmsd

Based on the fact it was sitting 15 years, I am guessing the major culprit was the dirty/bad injectors.

Yes, he should have mentioned that in the first post!

[Bert87]

Originally Posted by mysocal911

Most likely it was stuck injectors, i.e. a common problem when an engine sets for a long time,
and not a bad DME ECM. You could have verified that the DME ECM was not the problem
by following the suggestion up-thread of removing the temp sensor to provide a longer
injector pulse width thus having a brighter noid light while cranking.

In any case, you saved not having to send it out for testing or worst case having it rebuilt when
it wasn't necessary.

I did the noid test with all injectors unplugged and the cht sensor unplugged/jumped. Completely dark. Verified wiring by jumping pins 14&15 to ground on DME connector resulting in noid light flashing and injectors clicking.