odonnell

After thinking about it - if the tach is working, the sensors and DME have to be ok. Why? Because the tach gets it's "signal" piggybacked from the coil ground, DME pin 1. So the DME is trying to pulse the coil at the right frequency, so therefore, the issue must be after the coil ground wire.

944Ross

I had a coil that was fine in cool weather, and short trips, but every time I went on a long trip (>200 miles) it would start doing exactly the kinds of things yours is doing. It apparently would short out internally when it got good and hot.

Dougs951S

Precisely what I was thinking, that it's heat related. It's been fine around town, and only acted up after the car had been running for over an hour. I'll find out this weekend when I get a replacement coil from Michael (Thanks buddy!)

Dougs951S

Car is back to running perfect with a new coil. Thanks a bunch to Michael for the correct diagnosis and the part!

951Dreams

Awesome, and thanks so much for not leaving us hanging!

Dougs951S

The problem returned today (though not nearly as bad as before) on an hour long drive into the country. This time the car wouldnt really die, but it was missing randomly. I visited with a friend for a couple of hours and it did not do it on the way home. I'm frustrated and I don't know where to look next, it obviously isn't the coil since I just replaced it. It still seems to only happen on long drives since it's been fine driving for a few weeks in town. Not sure what to think now, but I need this issue nipped in the bud for good.

odonnell

Is the tach still up? If so, I'd replace the ignition wires and cap/rotor. Not a lot else it could be, assuming you still have fuel.

Dougs951S

yea same as before, tach still up. It has to be ignition wires/dizzy/rotor/power or ground wire to coil. one of the above.

edit: could the problem be in the DME? I guess not if the tach is running?

Dougs951S

See next post

Dougs951S

Let me recap: The car has a severe, random, intermittent miss/stalling issue. it'll be running fine, then randomly miss on all 4 cylinders and try to stall. The pedal will go dead and the car will freewheel down in gear as if someone shut the key off, except that the tach will stay up. Pumping the pedal will produce pops like its TRYING to run but obviously is either not getting enough fuel, or it has an extremely weak spark. Usually after a few seconds of this, the motor will suddenly return to life and I'll get a really strong fuel smell which makes me think something is causing the motor to lose spark. once power returns, it will run perfect for 5 minutes before it happens again. the miss is in no way engine speed or load dependent but seems to happen more when the engine gets good and hot. ive replaced the coil and the fuel pressure regulator and its still happening. I rely on this car and im at my witts end, can you guys help me troubleshoot this. If its losing spark but tach is up, where are the possible places the issue can be?

Things I know it CANT be: Ignition coil, DME, speed and reference sensors, ignition switch, distributor and rotor, fuel pressure regulator. That essentially leaves nothing left as a potential source on the ignition side of the equation since there really are not any other ignition related components. I'm starting to wonder if this is a fuel issue...lets start thinking about that possibility. On that end, there is: Fuel pump, secondary coil in the DME relay feeding the fuel pump, fuel injector drivers in the DME...

Turbodan

what does the rotor and cap look like? that is my guess.
another question is if the car is misfiring and you wait a few hours, does that correct it? I had a diaphrapm fail in a fpr to a vacuum hose and was pouring gas on my ecu on my 951.

Dougs951S

just replaced the fpr yesterday because i know it can cause issues just like I describe (and it was starting to fail, as evidenced by fuel being present on the vacuum line side of the diaphram). that did not fix it. I just pulled the cap and rotor, they lare low mileage and look excellent and I wouldnt think a bad cap or rotor would cause my symptoms, when power cuts away for several seconds it does it instantly and stays dead for several seconds before instantly returning, if you drove the car you'd understand why I'm certain that isnt the issue. I also just replaced the dme relay 5 minutes ago, hopefully that was it. my new theory is that the relay was suffering a temperature related fault in the coil that powers the fuel pump.

StoogeMoe

My guess would be that you are losing power to the coil. This can be tested by running an alligator clip wire from the positive battery post to the black wire on the coil. The only downside is that you can't turn off the engine with the key. You'll have to pop the hood and yank the wire.

If that doesn't work, then clean your connections on the plug to the AFM.

Intermittent problems are a pain. You'd rather just have it fail so you know what to fix.

Dougs951S

yeah this was my other thought, alluded to by Spencer a few weeks back. What gauge wire is appropriate to test this? If that IS the case, then I assume the solution is simply to run a new wire from the ignition switch to the coil?

StoogeMoe

I use standard automotive 18 gauge wire. I actually had this failure in my car once and now carry that jumper in my glove box. Don't worry about running a new wire until you confirm that is the problem.