DonD964

Hi everyone,

I'm baffled on this one....I'll try to keep it short.
HISTORY
Engine has been fully rebuilt and was running fine for past year in garage & driving up and down the street.
I then drove it to a shop for headliner work
It had been backfiring out of the exhaust a bit at low RPM but seems to smooth out when driving.
Drove it 7 miles to the shop and 7 miles back (first actual drive since the rebuild)
Got it home, tried to restart it the next day and that's when the problems started.

ATTEMPTED RESOLUTION
Thought it might be fuel related....
Drained the gas tank.
Tested the fuel pump after the fuel filter which is working great
Checked fuel pressure which shows within spec when idling but the needle jumps up and down due to erratic idle

I haven't changed out the fuel regulator bc most of the posts read that if it doesn't leak it must be good.
It seems like the fuel pump primes the engine, it starts, uses that fuel and then it dies and won't restart.
If I wait and come back to the vehicle after 15 minutes, it will start again but then the cycle repeats.
I posted a video...any help would be greatly appreciated!

Don

systemsc

Check the ignition system, i.e. the spark wires, plugs, distributor caps. Unplug one ignition module at a time, and run on just one.

DonD964

HI Thanks for the quick response!
Engine has new plugs, wires and caps.

If I isolate one of the modules what can I expect?
I haven't done that bc I figured if it can't run on two, how will it run on one module?
Thanks Loren!
Don

systemsc

It'll help isolate an ignition problem to one of the two systems. The 964 DME ECM is very sensitive to high voltage ignition radiation, e.g. via the Hall Sensor.

newsboy

Have you swapped the DME? Possible failing flywheel speed sensor?

LM964

Agree re checking the dizzy caps but definitely check the rotor arm for wear too - will also contribute/cause rough idling.

Good luck

DonD964

Hi Steven,

Thanks...I did swap the DME (both of them with no difference).
Don

jreifler

I’m hunting the same issue in a separate thread. DME relay is my next attempt. I similarly installed new caps, rotors, and coil plugs. I have coils on order as well, but they’re impossible to find right now.

jreifler

I similarly did this test without knowing what it would tell me. In my case, it ran poorly on either module. I guess if it ran flawlessly on one, you’d know you needed to replace the other coil / plugs / wires ?

DonD964

Hi,

Thanks for letting me know in case I need new coils...
Don

540964

Fit a 993 coil.



Retrofit thread:
https://rennlist.com/forums/964-foru...nto-964-a.html

RW964

Check the ignition system, i.e. the spark wires, plugs, distributor caps. Unplug one ignition module at a time, and run on just one.
__________________
Loren

I would try this first easy to do just reach down and unplug a mod and see how it runs I do it while the car is running.. As Loren stated my car was doing the same thing " a 90 " and I could not figure out for the life of me what was going on so I unplugged one module car ran the same like @$# plugged it back in unplugged the other module and the car ran like a top.. The car will run off of on system great so if you have problems with one cap or coil you have 100% backup .... You can tell just down on power but runs good

RW964

Please let us know what you find out as always good to have knowledge

RW964

" I similarly did this test without knowing what it would tell me. In my case, it ran poorly on either module. I guess if it ran flawlessly on one, you’d know you needed to replace the other coil / plugs / wires ? "
__________________ What I ended up doing on my car was swapping out the ing module as I plugged in the wire from the module from suspect bad system and the car ran great showing my that the coils wires caps etc. were in good condition and I just need the module was like 25 American so I have an extra

DonD964

Thanks for letting me know...Do you know what it is with the 993 coils that makes them better?