Need help with speedometer and odometer
Thread Starter
Safety Car
Joined: May 2001
Posts: 4,426
Likes: 0
From: Liberal KS
Need help with speedometer and odometer
Just got the Vette back from the shop (long story!) and I need help with getting the speedometer to work. Recently, a FelPro ECM was installed to help with the engine driveability issues. Engine runs great, problem is that the speedo and the odo no longer works.
My mechanic said that I need to check into a speedometer shop and buy some module that I will need to have installed in order for the speedo to start working again. He mentioned something like a DRAM ? module. Anyway, I am no longer speaking to my mechanic (check this thread for more details http://forums.corvetteforum.com/zero...78004#5478004) so I am desperately seeking this module so that my speedometer and odometer can work again.
Any suggestions are greatly appreciated. Thanks in advance.
My mechanic said that I need to check into a speedometer shop and buy some module that I will need to have installed in order for the speedo to start working again. He mentioned something like a DRAM ? module. Anyway, I am no longer speaking to my mechanic (check this thread for more details http://forums.corvetteforum.com/zero...78004#5478004) so I am desperately seeking this module so that my speedometer and odometer can work again.
Any suggestions are greatly appreciated. Thanks in advance.
3rd Gear
Joined: Oct 2004
Posts: 3
Likes: 0
RE: Speedo / Odo
I'm having the same problem. 
Replaced ECM/PROM, DIC and VSS on my 89. With as many other owners having the same problem someone should have a solution / fix for it. He/she would make a number of people VERY happy! 
Replaced ECM/PROM, DIC and VSS on my 89. With as many other owners having the same problem someone should have a solution / fix for it. He/she would make a number of people VERY happy!
Melting Slicks
Joined: May 2000
Posts: 2,148
Likes: 1
From: Chandler AZ
Ya know what's weird is that the VSS feeds the instrument cluster first (also FX3 if you have it), then the cluster feeds the ECM.
Pin C15 on the cluster grounds one side of the VSS, then D11 is the sinusoidal input frin the VSS (4000 pulses per mile).
Then the cluster outputs a signal at 1/2 frequency (2000 per mile) to the ECM from pin D12 by grounding this pin. The original ECM has this input at A10 pulled normally high (12v).
Only thing I can think is maybe the FelPro is shorting out the signal from the cluster; I would find and disconnect this wire D12 at the cluster (brown/white) or ECM harness A10 (brown).
Technically an engine management system doesn't need to know how fast you're going; original ECM only used this for torque converter lockup (1 to 4 upshift), mileage readout, and canister purge.
Pin C15 on the cluster grounds one side of the VSS, then D11 is the sinusoidal input frin the VSS (4000 pulses per mile).
Then the cluster outputs a signal at 1/2 frequency (2000 per mile) to the ECM from pin D12 by grounding this pin. The original ECM has this input at A10 pulled normally high (12v).
Only thing I can think is maybe the FelPro is shorting out the signal from the cluster; I would find and disconnect this wire D12 at the cluster (brown/white) or ECM harness A10 (brown).
Technically an engine management system doesn't need to know how fast you're going; original ECM only used this for torque converter lockup (1 to 4 upshift), mileage readout, and canister purge.
