Intermittent Engine Stall Options

[ThinAir]

I previously asked about swapping my ECU to troubleshoot a intermittent stalling issued (http://www.914world.com/bbs2/index.php?sho...=347323&hl=). I've been working on trying to pin this down, but no luck so far.

The current behavior is that the engine will suddenly shut off. If I'm driving down the road (in gear with clutch disengaged), it will often start back up on it's own. If I'm coasting down a street to come to a stop (clutch engaged) the oil& generator lights will come on, but if I let the clutch out the engine will restart.

What I've done so far:
Cleaned every contact on relay board and all relays with Dremel wire wheel
Replaced coil, pertronix and rotor
Replaced cylinder head temp sender (and swapped out 300 ohm resistor)
Ensured that injector points connector is secure on the distributor
Re-crimped connectors on 4 wires that connect to the positive terminal of the battery

The problem can occur after running fine for an hour or within minutes of starting a test drive. It doesn't match up with any event like hitting a bump and doesn't seem temperature related. I've previously checked the fuel pump electrical connections (my pump has been relocated to the front).

I have a spare ECU that I'm going to try tomorrow, but I figured it was worth asking if anyone has any other things to look at. I'm leaving for Red Rocks Classic on Thursday and would really love to know I can trust this car.

[mark04usa]

When the problem occurs, does the tachometer drop instantly to zero?
If it does, you likely have an ignition problem. (IMG:style_emoticons/default/beerchug.gif)

[rjames]

I had a similar thing happening. Sometimes it would stall right away, other times I could drive for over an hour before it stalled. Replacing the injection harness <I think> made it go away.

Something easy to check: Make sure your ground wires on the injection harness are all connected and making good contact. There are three grounds from the harness that all terminate at the middle of the rear firewall. You will need to remove the air filter box to see them.

[ThinAir]

Yesterday I decided to do the ground wires and pass for now on swapping the ECU. Cleaned the contacts with my Dremmel wire brush and reconnected. Moved wires to different ground connectors to help ensure a good connection. Test drove for an hour with no hiccups at all. Too soon to say for sure, but it seems promising.

Since the problem hasn't reoccurred, I can't say if tac goes to zero.

Thanks for the suggestions!

[ThinAir]

Thanks to @JamesM for following me on the RRC Saturday drive and noticing that I had puffs of black smoke from the tailpipe. These corresponded to hesitations from the engine. He suggested that it was likely my MPS.

Once back home, I confirmed that I had a spare compatible MPS (turns out I had it in the trunk at RRC). I tried this MPS and the problem went away. In addition, I tested my MPS and confirmed that it will not hold vacuum.

The bonus in all this is that with the "new" MPS I have been able to use my exhaust gas analyzer to set the CO level. It was so rich previously that I could never get it down to 3% CO. In addition, I've gained a new appreciation of how the FI system works.

I had told my wife that even if I wasn't confident that I had fixed the issue, I was going to tow the teener to RRC just to get the input from others at the event. I'm sure glad that I did. If you are ever wondering whether these kinds of events are worth the effort to attend, you'll be amazed at the wealth of knowledge which is present.

[JamesM]

Thanks to @JamesM for following me on the RRC Saturday drive and noticing that I had puffs of black smoke from the tailpipe. These corresponded to hesitations from the engine. He suggested that it was likely my MPS.

Once back home, I confirmed that I had a spare compatible MPS (turns out I had it in the trunk at RRC). I tried this MPS and the problem went away. In addition, I tested my MPS and confirmed that it will not hold vacuum.

The bonus in all this is that with the "new" MPS I have been able to use my exhaust gas analyzer to set the CO level. It was so rich previously that I could never get it down to 3% CO. In addition, I've gained a new appreciation of how the FI system works.

I had told my wife that even if I wasn't confident that I had fixed the issue, I was going to tow the teener to RRC just to get the input from others at the event. I'm sure glad that I did. If you are ever wondering whether these kinds of events are worth the effort to attend, you'll be amazed at the wealth of knowledge which is present.

Glad I could help and that you got it sorted out!

[ThinAir]

Well I spoke too soon about the problem being resolved. About 2 days later it was back again.

Since the ECU was the only component yet to be replaced (and I now had a spare ECU), I swapped parts. When I pulled the connector out of my original ECU, I discovered a wire that was cut/worn through and sticking out of the harness. I taped it up and repositioned it where it belonged, then installed the "new" ECU.



I have now run the car often enough that I can say confidently that the problem is gone. I haven't put the old ECU back in so that I can confirm that the wire was the problem, but since I don't see anything conductive that it would have contacted I'm thinking it really was the ECU.

It's nice to have confidence in my teener again!