Speed Sensor Connects Into What??

weedhoppin74 · 03-25-2004, 06:22 PM

Hey gang need help. I have a 1986 944. When I bought this car it had a rough idle sounded like it was at a constant backfire. After I drove this car home it stoped running. So I did some searching on the web and ended up changing out the DME relay. The car started and still idled rough. After a few days of pondering why this car is running horribly I noticed a wire that was cut and half a** put together. After re-wiring this the car started and purrs like a kitten. Anyhow, now to my BIG problem. For the past few days my car will start and then stall. I just found out the wire that was cut was the female side of one of the speed/reference sensors. The sensors aren't the problem, the problem is the female part of the sensor was the wire that someone cut. So, needless to say my problem isn't the simple change the sensor it's the oh-no why did someone cut this wire!!!! Does anyone know what this large group of wires is called or how to find out if this wire can be replaced. Any help would be great for this helpless first time porsche owner.

ae1969 · 03-25-2004, 10:03 PM

Was it cut all the way..... ???

I can't remember if the wire is shielded or not? What is funny I just finished putting a new set of reference sensors 1 hour ago..... hehehe

Unfortunately the wire goes into the engine wiring harness. You could buy a used harness on ebay....Not a fun thing to swap out if the engine is still in the car.

This could definitely explain your intermittent stalling.............. you should of seen the shape of my sensor wires............. OH THE HUMANITY

DannoXYZ · 03-26-2004, 03:20 AM

There are three important wires on the back of the engine by the firewall:

- speed sensor
- reference sensor
- O2 sensor

If the wire that was cut had a round connector, then it's the O2-sensor. The other two have a rectangular connector. And they are ALL shielded coax cables. That's because the signals are very, very low and intereference from the coils can cause problems.

Now, if someone had cut into any of these wires, you gotta be really sure that the outer shielding braid doesn't have some eeny tiny little strand of wire that can contact the center conductor.

From your symptoms, sounds like someone tapped into the O2-sensor line to drive an O2-sensor. Really, really bad idea because a bare wire running out in the engine-bay will pick up a lot of interference and make your display worthless anyway. Best to tap in to the O2-sensor inside the DME-connector itself after it's been separated from its surrounding shielding braid.

Ok, so.... take apart the wiring where the splice occured and verify that the inner conductor is whole, with no shorting from any of the surrounding shielding. Then wrap the center connector with some electrical tape. Pull the shielding braid back over the splice and tape all of that down as well.

If either of your speed or reference sensor cables were bad, you'd get no running at all.

weedhoppin74 · 03-26-2004, 04:20 AM

Ok, The wire that was cut came from the wiring harness from the firewall. This wire was completely cut, cut off the engine wiring harness!!! It is the female with the rectangular end on it. The first time I re-wired it I just did a simple re-gathering of the wires and wrapped each one separately. Ran great with no stalling or problems for about two weeks. Then on Monday, I started my car drove to the time clock shut the car off and then it would not start!! After about 2 hours of trying to get this car to start I heard the same high pitch sound that I heard when I found that half *ss wire job someone did. After fooling with the wire, I got the car to start. So I finally made it home and pulled out the good ole soldering iron. So, I re-did the wires again. Car started and ran fine for two days. Now, it starts and stalls after idling for about 5 minutes. It starts right back up. Since I have the weekend off I will pull off the tape and soldered the wires. Hopefully I just missed a little braid from the shielding. This wire was the pain in the but. It only had a tiny tiny little piece of a wire to work with. So I had added some wire to give me something to work with. When I go to look for the wiring harness that I need that runs from the firewall what do I look for? I tried looking it up last night and could not find it. All I could find was the speed / reference sensors. Does anyone know the name or part number that I would need to replace this. Thanks for all the help so far. You guys are great!

ae1969 · 03-26-2004, 08:40 AM

Uhmmmm looks like someone cut the reference sensor feed from the dme..... Like I mentioned it is part of the wiring harness. You can't order the shielded cable on its own. Your only hope is to splice back the original wiring. Unfortunately you may have intermittent starting issues until you replace the harness.

I would not add unshielded wire to increase its length. Like danno mentioned the noise generated by using an unshielded cable will affect the signal.

Your best bet is to find a used harness on ebay.