DME relay is flickering

[edbaus]

So, My 86 944 is having an issue.

It starts and runs great. It will not drive very well.

Even as it sits and idles it seems to turn on and off. Just for a moment. If you put your hand on the DME relay you can feel it turn on and off.

I have swapped out DMEs, DME relays, air flow sensor, speed and reference sensor, checked the ignition. Still have the issue.

I am looking for the next thing to try.

Thanks

Ed

[TibetanT]

Hey Ed:

I didn't know you had a 944?

My thoughts right now are, you may have a bad DME relay.

[tnporsche]

I elliminated the dme relay!

Well sortof, I coverted it to a much more reliable 40 amp SPST available at any autozone. ( $5.00! ) If your interested I can post how.

[edbaus]

Yes. I have it to go 944Cup racing. All set except for this problem.

I used a jumper wire and jumped it out. Still have the same problem. My understanding is that the DME actually powers the relay, not the other way around.

Thanks

Ed

[tnporsche]

Originally Posted by edbaus

Yes. I have it to go 944Cup racing. All set except for this problem.

I used a jumper wire and jumped it out. Still have the same problem. My understanding is that the DME actually powers the relay, not the other way around.

Thanks

Ed

If the jumper did not help, then yes eliminating that dog! of a relay wont help. :-)

Although even when new, I question how good that relay is? I went through 3 shutdowns about 12 or more no starts. Usally when it was dog a%$ cold , or hot. I would put the jumper wire and it would start or go. I started using backup dme relays. I had one used and one new, rotating them when it failed. It was Interesting I noticed if I put the original one back in, then it would work again also. I have been running on the auto-zone relay for about six months. Not a single failure yet, Ha !take that bad designed relay!

So if your sure its not the relay how about.

Have you swapped the dme out?

How about ref sensors and connections?

Grounds?

[alantica]

Originally Posted by edbaus

So, My 86 944 is having an issue.

It starts and runs great. It will not drive very well.

Even as it sits and idles it seems to turn on and off. Just for a moment. If you put your hand on the DME relay you can feel it turn on and off.

I have swapped out DMEs, DME relays, air flow sensor, speed and reference sensor, checked the ignition. Still have the issue.

I am looking for the next thing to try.

Thanks

Ed

edbaus,

I would suspect a vacuum leakage in the fuel injection system, intake manifold or vacuum hoses. You have covered all of the electronics plus the AFS. Have you checked the spark plugs? Are they fouled?

[944 Ecology]

Check your ignition switch.

[edbaus]

AND THE WINNER IS......


The ground.


Despite checking, cleaning, and fussing with it, when I put a jumper cable between the ground, the chassis and the motor the problem disappeared.

Now if only I can get that reference sensor bolt that I dropped into the clutch inspection hole back...

Thanks

Ed

[edbaus]

OK,

New answer. The ground was not it.

Turned out that the car had solid core wires causing an RF problem with the speed sensor. New one on me.

Thanks

Ed

[Razorback1980]

Hey Ed,

Could you please explain what you mean by a solid core wire and how the reference got the wire? Just trying to understand....and how did you figure that out?

[edbaus]

My nephew can explain it better, but solid core wires, although do a good job of transmitting spark energy, also emit a HUGE amount of RF noise. Enough noise that even the well shielded speed and ref sensors can get interfered with.

Solid core wires should only be used with magneto or points style ignition systems. Nothing with a brain.

[Razorback1980]

Are you saying solid core ignition wires? Sorry for being confused here.

[edbaus]

Yes, the wires that run from the distributor to the spark plugs.

Thanks

Ed