Crank Position Sensor Problem

I now have 250 miles on my rebuilt 3.4L normally aspirated. All seems to run well with one exception. The original Crank Position Sensor had bad insulation on the wires. I repaired the wires but wanted to replace it with a new one. I ordered a new one and replaced the sensor. When I started it up, it would not rev ocer 3000 rpm. I suspected a bad sensor and sent it back. Well. I got a new one from another company and it does the same thing. It is as if you hit a rev limiter at 3000 RPM. If I put the old one back in, it works fine. I called the vendor and they said that I have the correct part. Has anyone neard of this? I have a 1999 996 3.4l with tiptronic.

Maybe try running dedicated wires for the CPS directly from the DME. What P/N did you buy?

I got this 986.606.112.02.

Yep that's what I see... but you put your old one in and it works??? Maybe your torque converter or flywheel is damaged, would be hard to believe though..?

So the original one with the repaired wires works fine but the replacement(s) are limiting the revs?

Yea, I do not understand it. This is my second sensor. When I got the first one and put it in I just assumed the new sensor was bad so I sent it back. I put the old one in and ordered another new one. Popped it in and instant rev limiter at 3000 rpm. The original Bosch part number was 0261210149 and the Porsche Part number was 986.606.112.01. The replacement Bosch part number is 0261210204 and Porsche part number 986.606.112.02. According to the AutoAtlanta site this is correct by the Porsche number. I have read all the posts on others changing this part and it was just plug and play. Why does mine have to be different?

I also had this happen when the spacing between the sensor and toothed wheel was incorrect. Try a shim under the sensor to space it out a bit and see what that does.. Or like I ha emailed, have the ECU flashed.

Does anyone know what the air gap is supposed to be on the crankshaft speed sensor? I found all kinds of information from Bosch but nothing that tells me what it should be?

I did a little expermentation today with the crank position sensor. Comparing the old one to the new one I found no difference between the physical dimensions. Especially important was the distance from the flush side of the mount to the tip of the sensor. Both were exactly the same. I took some measurements of the resistance and see that the new one is 938KOhm compared to the old at 915KOhm. This being the case, the new one would have more windings and a higher output. On the Bosche site the output was determined by the type of metal the toothed wheel was made of, the tooth rotational speed and the air gap between the sensor and the tooth. The only thing that I have control over is the air gap. I slipped a washer in at 60 thousanths and fired her up. It would rev the full range but felt a little uneven. I decreased the spacer to 30 thousanths and got excellent results. So, Jake was right with the spacing and I will fill in a few keywords at the bottom for anyone else that runs into this and hopefully save them time and aggravation. Oh, I also added an O-ring to the sensor since I had a gap now between the probe hole and the sensor just to keep the crud out. crankshaft position sensor crank sensor RPM sensor crank pulse sender crankshaft pulse sensor RPM pulse sensor flywheel position sensor flywheel sensor

Nice work. Even though you o-ringed it, isn't there already a big gaping hole though in the bell housing right near the CPS?

I do not see one there. And I do ot remember seeing one there during the engine rebuild.

Might want to put on some anti-seize too. I remember when I had to replace my pulse sender during the engine work I did. Now my car had been through 8+ Chicago winters, but even though the pulse sender body is plastic mine would not come out. Tried prying it out, drilling it and using a screw to pull it out. Finally had to drop the engine and pull off the transmission and the flywheel and beat the damn thing out with a small hand sledge. It came apart into pieces as part of this process. I did use some anti-seize on the new one which slipped right in after I cleaned up the hole. What a PITA that was.