My Speed and Reference Sensor Thread
 

So I have had an issue with my 951 since I got it. When I first bought it and knew absolutely nothing about the car and how it works, sometimes it wouldn't start, then I finally started wiggling wires around under the hood and BAM it would start.

After I sorted the car, I knew they were the speed and reference sensors that I was wiggling and everything would come to life if it wouldn't start, so not a big deal.

Then the car was pretty much perfect, but would stall sometimes after warming up and being run, but ONLY at idle, i.e. I would be on the highway or driving around, normally when it got really good and warmed up, get off the highway, and it might stall on me at a stop light. Put the hazards on, open the hood, jiggle the speed and reference sensor wires right at the connector from the sensor to the DME wiring, close the hood, the car would start right up. And it would run normal, and it would never stall except at idle.

The wiring did not look good on the DME side, so I bought the kit from one of the two suppliers and ran new wires back to the DME with the new connections for the sensors. I thought I had the problem resolved. It sure seemed to not happen for a long time, but then it finally did again (I hardly drive the car at all, 500 miles a year if that), and it's done it multiple times since then.

Funny thing is, I had to go into the clutch before I replaced the DME wiring side, so I had the speed and reference sensors out previously and have re-gapped them when I put everything back together.

Last year I bought new Bosch sensors from Rockauto that was on close out, I have yet to put them in, but will when I take the car out of storage.

It's odd, because the existing speed and reference sensor wiring appears to be in good shape (like perfect shape), and this only happens at idle.....anybody BTDT and can tell me what I am missing?

Thanks.

Paul, I've had the same issue in the past, and a quick wiggle of the connector always fixed it. I also had an aftermarket DME-to-Connector wiring kit installed. I had replaced reference sensor in the past with no change.
I was about to replace the sensor and wiring again a few months ago. After replacing the sensor (I used an FAE brand, but had used this brand in the past), the car seems to be running fine. I drove an entire DE weekend with no issues.
So, it could be something as simple as a poor connection between the sensor and harness. Worth just replacing the sensor to see if that fixes it. It would be interesting to see if there is a difference in length between the Bosch and other sensors..

I wouldn't personally use an FAE sensor after seeing some with the shielding wire shorted to the sensor output. That's clearly a quality control issue when manufactured, and not intentional (since the car won't run that way). If an FAE sensor tests good on the bench, how can one be sure that an intermittent issue like this isn't just an intermittent version of the shielding wire grounding out the signal inside the sensor? I'd stick with Bosch personally. If wiggling the harness under the hood seems to always fix the problem, then I suppose you have to concentrate on the sensor and harness wires/connectors. You might also look closely at the fuel injector connectors. They suffer the same problem, and also kill the motor when bad. Check for tach bounce when it won't start -- that will help confirm if it's the speed/ref sensors or not. Also check to confirm the boost gauge goes to 1 when the ignition is on (and if not, consider the DME relay). If the problem is more random and doesn't always respond to wiggling the harness, you might also look for cracked solder joints on the DME.

So I pulled the 951 out of storage this afternoon, she started right up like normal.

Then it was idling while I was moving the other cars around and then died after about 3 minutes just as I was getting back in. Cycled the ignition, the boost gauge comes up to 1 bar, and then crank it and no tach bounce. Open the hood, jiggle the reference and speed wires on the sensor side just a bit and BAM comes back to life when the key is turned again. So it's either the connector between the harness and the sensor or it's the wiring in the sensor and changing the sensors will fix it. Tomorrow I will put this on the connections:

https://encrypted-tbn1.gstatic.com/s...RnxxM&usqp=CAY

I used that stuff when the driver's seat height adjustment would go up, but not down, and I didn't want to pull the whole seat apart to get to the switch, just sprayed that stuff from the outside of the switch and BAM it started working again and has yet to stop 3 or 4 years later.

dirty contact or possibly a broken wire?

I figured it today, or I believe I have. Once I took the connectors apart and sprayed them with the detoxit, then put it back together, the car would not start, no tach bounce. I just moved the sensor side of the wire, then the car fired right up, so I'm 99.9% certain it's an intermittent open on the sensor side, will replace the sensors soon. Sometimes just writing your problem down on the forum sure makes it a lot easier to solve.

I drove it about 40 miles today, the car is a hoot! But when I got back my 996, that car is just so much more comfortable in almost every way. But I LOVE my 951!

https://cimg8.ibsrv.net/gimg/rennlis...6a73a28a7e.jpg
https://cimg2.ibsrv.net/gimg/rennlis...f025b51d29.jpg

Long time no post, but I wanted to update this thread for the next owner of the car. After everything above, still had the issue where it would stall and had to wiggle the wires sometimes. I mention that I bought new speed and reference sensors but I had not yet put them in. I did put them in shortly after the post above in 2019 and I can confirm that it has never stalled since.

new sensor going in my 951 build as well. the wires were replaced recently and look like new.