ANDYZ28

I am in the process of restoring a 1990 IROCZ (5.0 TPI 5 speed)back to it's original configuration. But a couple unexpected of problems have come up.

1) Original ECM was missing (and engine bay gutted) when I aquired the car. I am installing a 1991 Z28 5.0 TPI 5 speed engine, harnesses, ECM, etc. The doner car was equipped with a 3.08 rear. I want to install a 3.42 rear which I already have. How do I get the speedometer, and ECM to read and indicate the correct speed?

2) I am also going the install the 140 MPH guage cluster from a doner 1990 IROCZ. Am I going to have any speed problems here?

Thanks, andyZ28

Berlinetta

theres a company that sells a electronic speedo adjustment box that splices in to your existing speedo wiring and allows you to adjust the signal from the VSS until your speedo registers the proper speed. I believe it can be found at summits website. That should allow you to tune around the gear changes and tire change. Im not sure about the new gauge cluster though.

samdog1232000

The speedo you acquired will be fine. All the speedos read the same but the different gears and tire size can throw it off. But for the speedo, you can use any of the electronic ones from 90-92 and you will be fine. The 90 Iroc came with a 140 speedo anyway so the one you have will be fine!

ANDYZ28

I managed to get this problem solved by changing the speedo drive and driven gears. The driven gear is part of the vehicle speed sensor, so I had to buy the whole unit. But it seems to work just fine.

I have not driven the car on the road yet because of the upgrades I am doing are rather time consuming and I am also taking pictures along the way to add to my CD.

Thanks for the help.