hockeydude

Hey guys!

The last few times that i have had my '87 951 out, it has run perfectly fine for a few minutes, then the engine just stops running (in gear, neutral, seems not to matter). It then takes a few tries turning the key to fire back up... BANG! (Huge backfire?), then either runs fine or keeps doing this process.

Any idea what may be the cause of this? DME? TPS? Refrence Sensor? Other?

Thanks a lot guys. I hate having a car that i can't depend on. :-(

toddk911

Backfire is just a bunch of fuel when trying to restart.

But I would start with ref sensors and then check others you listed. DME would be only if died and would not re start.

951Doc

It might still be the DME, but somewhat indirectly. Check the integrity of the DME power cables to the positive terminal of the battery. A loose connection there drove me crazy for a while - the car would run fine then out of the blue quit. Just by luck noticed it, tightened it, and voila!

I agree with the reference sensor as a likely culprit. An oscilloscope is a great tool to have in the workshop. You may be able to pick one up for $50 on craigslist, and you'll feel like quite the pro using it to diagnose electrical problems. See Clarks Garage for more on the subject.

951Doc

schip43

Fuel pressure?

piperporsche180944

I have a similar issue, I was WOT on a highway on ramp and it shut off and wont start. No spark. Im starting with the easy stuff first, cap, rotor, dme relay, etc

I wish you luck friend.

xsboost90

do you have a spare DME relay? it could have a bad contactor on the ignition side of the relay- has two- one for spark/one for fuel- and its loosing spark while driving, which would flood the engine slightly- then when you go to start it finally gets spark and boom- backfire. You can try taking the top off of the DME relay and getting some small pieces of cardboard and sticking them in there to hold both contacts closed. Then see if it still does this.

quinnfiske

I had a similar problem and it turned out to be the DME itself. The circuit that sends a signal to the ignition coil failed. I could hook up a timing light and shine it in the inspecion hole for the cam sprocket. With the engine idling, the timing would retard itself until the engine stalled.

An oscilliscope would be a better way to watch the signal, but I don't have one.

Keithr726

From what I recall I had something similar happen which was caused by bad speed & reference sensors. Also take a good look at the wiring because mine was really bad so I cut and spliced a bit. I plan on replacing the whole harness with the LR kits over time; after 20 years my harness is quite tired.

hockeydude

thanks for all the ideas, guys! I'm going to order a set of sensors and a spare DME relay from Lindsey, and see if the DME relay does the trick... if not i'll change out the sensors and hope that does it. :-)

INURGRL951

Check the female side of the reference sensors i had a busted wire creating the same issue but you have to peel off the old wire lome to see right at the bend it tends to break.

Mighty Shilling

I recently had an issue where I'd be driving and it'd stall out, crank, nothing, then fire up again. turned out to be the AFM. Check that, open the door and if it squeaks, replace it.