Speedometer not working proprely
Thread Starter
7th Gear
Joined: Jul 2013
Posts: 7
Likes: 0
Speedometer not working proprely
Hello every one I have a 1987 corvette. I have a huge problem my speedometer is not working properly. I have a new ECM, new speedsensor, new cluster. I replace everything... Chevrolet does not want to help me. The speedometer work just fine sometime and jump around some other time. My car is an auto.
Do you have any ideas? I am desperate...
Do you have any ideas? I am desperate...
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
Patience !! You waited less than an hour for a problem with a 26 year old car.
You need to start with the work that you've done and that I'd say is start with the VSS. Post the part # of the VSS that you bought for starters, I'd suggest that the operation of the VSS be confirmed, also the condition of the drive and driven gear in the transmission. That means you need to remove the VSS again but it's the first leg of what you've changed. You changed all of the mentioned pieces to attempt the repair? Do you have a FSM?
You need to start with the work that you've done and that I'd say is start with the VSS. Post the part # of the VSS that you bought for starters, I'd suggest that the operation of the VSS be confirmed, also the condition of the drive and driven gear in the transmission. That means you need to remove the VSS again but it's the first leg of what you've changed. You changed all of the mentioned pieces to attempt the repair? Do you have a FSM?
Thread Starter
7th Gear
Joined: Jul 2013
Posts: 7
Likes: 0
Sorry about that 
So What I have done is the speedsensor has been replace for another one (original part), the ECM has been replace this summer as well, the Cluster has been rebuilt in august.
I also test the speed sensor and the ECM with a big snap on computer. The signal drop for both. However if I unplug the cluster the signal from the speedsensor stay stable. However the cluster just has been replaced.
So What I have done is the speedsensor has been replace for another one (original part), the ECM has been replace this summer as well, the Cluster has been rebuilt in august.
I also test the speed sensor and the ECM with a big snap on computer. The signal drop for both. However if I unplug the cluster the signal from the speedsensor stay stable. However the cluster just has been replaced.
Thread Starter
7th Gear
Joined: Jul 2013
Posts: 7
Likes: 0
Patience !! You waited less than an hour for a problem with a 26 year old car.
You need to start with the work that you've done and that I'd say is start with the VSS. Post the part # of the VSS that you bought for starters, I'd suggest that the operation of the VSS be confirmed, also the condition of the drive and driven gear in the transmission. That means you need to remove the VSS again but it's the first leg of what you've changed. You changed all of the mentioned pieces to attempt the repair? Do you have a FSM?
You need to start with the work that you've done and that I'd say is start with the VSS. Post the part # of the VSS that you bought for starters, I'd suggest that the operation of the VSS be confirmed, also the condition of the drive and driven gear in the transmission. That means you need to remove the VSS again but it's the first leg of what you've changed. You changed all of the mentioned pieces to attempt the repair? Do you have a FSM?
Pardon my ignorance but what is a FSM? Nevermind found it. No I don't.
Last edited by Brett Jetstarkiller; Nov 25, 2013 at 06:50 PM.
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
If you're mentioning that if the cluster is removed and the VSS signal at that time is correct and stable it would hint that the issue is with the cluster. That's only based on your comments of the check with "big" Snap-On computer. Where did your cluster come from?
If you had the FSM you could see the cluster is the "first stop" from the VSS - for others it's to the ECM and then cluster but yours I believe the cluster is the "first stop" and the ECM is supplied from the cluster.
If you had the FSM you could see the cluster is the "first stop" from the VSS - for others it's to the ECM and then cluster but yours I believe the cluster is the "first stop" and the ECM is supplied from the cluster.
Last edited by WVZR-1; Nov 25, 2013 at 08:18 PM.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
There are a couple of tests you can do to verify where the problem is.
One is to measure the resistance of the VSS at the cluster end of the harness. Take the cluster out, stick some straight pins into sockets D11 (yellow wire) and C15 (purple wire). You should measure the resistance of the VSS. It's basically an AC motor operated as an alternator and you're measuring the resistance of the VSS winding. I got 435 ohms on my car. This test verifies that the VSS, connectors and wiring are all good.
Another test you can do is to use a drill motor to spin the VSS and measure the output voltage with a voltmeter in the AC voltage mode. According to Gordon Killebrew's cluster manual the voltage should be between 2 volts and 28 volts, depending on the speed (it goes up as the speed increases). Or you can use an oscilloscope:
One is to measure the resistance of the VSS at the cluster end of the harness. Take the cluster out, stick some straight pins into sockets D11 (yellow wire) and C15 (purple wire). You should measure the resistance of the VSS. It's basically an AC motor operated as an alternator and you're measuring the resistance of the VSS winding. I got 435 ohms on my car. This test verifies that the VSS, connectors and wiring are all good.
Another test you can do is to use a drill motor to spin the VSS and measure the output voltage with a voltmeter in the AC voltage mode. According to Gordon Killebrew's cluster manual the voltage should be between 2 volts and 28 volts, depending on the speed (it goes up as the speed increases). Or you can use an oscilloscope:
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