Solved a stupid tachproblem
Thread Starter
On The Tree
Joined: Jul 2004
Posts: 166
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From: Stockholm, Sweden
Solved a stupid tachproblem Since I got my car running the tach hasn't been working. No movement at all on the needle.
I checked the connection and it had 12V.
I borrowed a oscilloscope from a friend and there was just a straight line of 12V, no signal at all.
This made me start checking the other end of the connection. I have a stock harness that I have adapted. Mine is a 2001 Camaro. I got from a donor car the connectors and cables for C100, C101, C105, C220 and C230 so it was easy to connect everything without cutting in the engine harness.
So now to the solution. Tachsignal is from C105, white cable at pos G. The problem was that my C105 connector had a white cable at pos F, not at pos G. The PCM side of connector C105 has seven out of the eight pins connected but the body side has only four in use. See picture:
So not checking where the white wire came from I connected it to the tach and it didn't work because the white wire I had in my connector was for Cruise Control Engaged Signal.
When I moved the white wire from F to G I got a working tach.
Here is a shot on how the signal looks in the oscilloscope on idle. It is changed in the PCM to output a 8-cylinder signal.
I share this experience so hopefully others doesn't make the same misstake.
Jan
I checked the connection and it had 12V.
I borrowed a oscilloscope from a friend and there was just a straight line of 12V, no signal at all.
This made me start checking the other end of the connection. I have a stock harness that I have adapted. Mine is a 2001 Camaro. I got from a donor car the connectors and cables for C100, C101, C105, C220 and C230 so it was easy to connect everything without cutting in the engine harness.
So now to the solution. Tachsignal is from C105, white cable at pos G. The problem was that my C105 connector had a white cable at pos F, not at pos G. The PCM side of connector C105 has seven out of the eight pins connected but the body side has only four in use. See picture:
So not checking where the white wire came from I connected it to the tach and it didn't work because the white wire I had in my connector was for Cruise Control Engaged Signal.
When I moved the white wire from F to G I got a working tach.
Here is a shot on how the signal looks in the oscilloscope on idle. It is changed in the PCM to output a 8-cylinder signal.
I share this experience so hopefully others doesn't make the same misstake.
Jan
