2Cool68

After accelerating through 1st the car begins to hunt and search WAY erratically. Scanner shows speed jumping all over the place which is the cause. Switched the PCM still does it. Switched the actual speed sensor on the trans, still doing it. Anybody with some thoughts??? The engine and trans are out of a 2002 Trans AM that was wrecked. Could the output shaft be tweaked just enough to send the wrong signal to the speed senor?

Any help would MUCH be appreciated.

2Cool68

Im not sure if this is an electrical interference problem or bad ground either. The mechanic said that he completely disconected all wires to and from the trans and just had the scanner on it and the speed on the scanner still shows jumping all over the place. He did this to eliminate all the posibilities of a wiring problem. He still feels it must be an internal problem. Any thoughts??

streetfytr68

I noticed that your sig says 68 Camaro with an LS1. Is this an aftermarket digital speedo? If so, an uncalibrated or miscalibrated speedo will drive the computer crazy. It's weird because the speedo signal is output, so it should not have an effect, but I see it all the time. In most cases, an uncalibrated speedo just causes the trans to not upshift out of first. Try unplugging or snipping the speedo to sender wire and re-test. If you snip the wire you can add a male/female bullet connector so that you can connect/disconnect at will. This will be helpful down the road for calibrating the trans first and then calibrating the speedo.

If this is the problem, leave the speedo disconnected until you have the trans calibrated. With the trans sorted you will need to rough calibrate the speedo with the rear wheels on jackstands. Get it close enough that the trans shifts properly (i.e. I ran my Auto Meter speedo calibration counter up to 2500 pulses). Then you can go out on the street and do a proper 2 mile calibration.

Worth a shot anyway.