ahofam123

My 944 has developed a no-spark issue which seems to be linked to the reference sensors. Per clark's garage, I checked the resistance between the two signal terminals and got 1000 ohms on one sensor and infinite ohms on the other one (should be between 600 and 1600 ohms).


Before I go off and spend the $100+ on a new sensor, has anyone had any success in rebuilding their old ones or finding a generic aftermarket sensor?

Also, for the early cars, will a bad DME relay cause a no spark problem, or does it just control the fuel pump.

Thanks,
Tom

austin944

Perhaps you could get a used sensor for less than $100.

Mr. Avionics

Nope, bad relay doesn't affect spark. Without ref sensors the DME will not turn on fuel pump. Try wiggling the wires where they go into the plugs, I sometimes have a start problem, a simple wiggle and away I go. This happens very rarly. Appears to be an intermittent connection within the plug. Just haven't gotten arroud to looking at it yet, not really a problem. Check arroound for used sensors, sombody got to have some laying arround.
Good Luck.
Bill

MichelleJD

I replaced both of mine while the engine was out (no, you DON'T want to know what I've spent on this rebuild ) and have one of the old ones laying in the carriage house. I trashed the other one getting it out. Good news is I'll let it go cheap (free); bad news is I glued a washer to the bottom of it to calibrate my new ones. I don't know how hard it would be to remove the washer. BTW, do NOT move the bracket the sensors are in when you replace them. You'll have to recalibrate as well.

Jared944

Did you try adjusting them? I believe they are supposed to be .8mm away from the flywheel :P

Granite 944

I had the same condition on my '85/1 project car when I picked it up. It wouldn't startup. I checked the resistance values of the sensors (as per Clark's), and the reference sensor showed infinate on the meter. Its SHOT. I replaced that sensor, and it started right up. Nope, that sensor is toast, unless its just a bad connection at the amp connector. Agreed. Don't move the bracket. Spray a little (don't over do it) PB blaster around the top of the sensor, and gently turn it back and forth, while pulling up till it comes out of bracket hole. On re-install, make sure the amp connector female prongs are clean, and closed up enough to make good contact with the male counterpart, a dab of dielectric grease, and your good to go. Save the bad sensor, cut off the wire, and glue on a washer, and you now have a tool for setting the sensor gap. Thats what I did. Good luck!

Bart

There's some used ones on ebay right now for less than $10 (ten) bucks. Search under "944"

ahofam123

Thanks for the responses. Hopefully this is the only thing that is keeping it from sparking.

Also, thanks Michelle for offering your old sensor. I think that I've found a cheap one locally, but if it falls through, I'll let you know.

Its funny that the car started acting up when it did. I was living in Charlotte last semester for an internship and the 944 performed flawlessly as a daily driver. Then as soon as it returned to Atlanta, it refused to start. I guess that it was just afraid of Atlanta traffic.

robG

I recently replaced my speed and reference sensors with new ones. Checking the resitance values per clark's, terminals 8-23 and 25-78 have a resistance of zero ohms. Not good. I put the connectors on backwards (speed to reference and vice versa) while reconnecting, dumb I know . Could this have junked the sensors? In the interest of disclosure I did turn it over while they were hooked up backwards. I didn't adjust the mounting bracket while I was in there, AFAIK.

jns

I checked the resistance on the outer terminals of my old sensors per Clark's and got nothing, but the middle and outer ones checked out good. I replaced the sensors and got zero on the outer ones again and it later turned out to be a different problem I was having with wiring elsewhere on the car. Looks like I replaced my sensors for nothing but I still don't understand how I didn't get the readings per Clark's on the outer terminals but they were good sensors. Anyone else have this problem?

Zero10

robG, the DME reads a signal generated by the speed and reference sensors by a nice little property of magnets and coils of wire called induction. It actually generates the voltage. So, there is no way that hooking them up backwards could damage them.
I hooked mine up backwards, no issues at all.

jns,
That is a little odd. When you say the middle and outer ones checked out good, do you mean infinite resistance? Perhaps your meter was on the wrong range?

robG

Zero10,
Thanks ... I was leaning towards the same conclusion, but you never know with Porsches and electronics!

jns, I'm getting the same resistance readings that you were between the outer terminals, i.e. zero ohms resistance. What was the wiring issue that you had? Does your car now run with those same sensors?

Rob