C4 - 1991 don´t run

[Tomas Portugal]

Hi everybody
I'm Tomas from Portugal - Europe

I need help.
I've a C4 - 1991 and i've just installed a "Corvette Security Override System, VATS Code 4, 1986-1996" from Eckler's . The engine almost started but did not run. Only run with a direct linking.
I achieve invalidate the VATS, but the engine still does not work
The instrument cluster service does not illuminates and I don't have speedometer, trip odometer, fuel level, etc.
The manometers are working and i've some "check engine lights" on (like check gauges...). I think that i have a problem with the ECM...

what's your opinion? what i need?

Thanks a lot for your time.

Tomas Marques
Portugal

[1990-C4-41001]

Hello Tomas:

Sorry you are still having problems.

You may have an ECM problem but the CCM computer is what drives the LCD display and also can cause a no start condition by not turning on the fuel injectors.

First check the ECM Fuse (3 Amp) CLSTR (Cluster) Fuse (5 Amp), A/C (Air Conditioner) Fuse (25 Amp) and the CCM Fuse (10 amp) on the fuse panel located on the right side of the dash. Check them with an ohmmeter set to the Rx1 scale and make sure they all are good. If all of those fuses check good, check all remaining fuses because some fuses are multi-function and current flows through them to accomplish their primary purpose but also secondary purposes.

If all fuses are good, you will need to place your car in the diagnostic mode and search for ECM codes.

There is a web site that explains how to do this:

C4 Corvette Diagnostic Code Recovery Techniques

Since your speedometer display is not working, you will need to follow the procedure at the top of the page where you short pins A and B of the ALDL connector to one another. (The connector is located just above where your right knee would be when you are sitting in the driver's seat. It has two rows of pins, 6 pins each. You use a paper clip to short the pin farthest to the right on the row that is farthest away from you (this is Pin A) to the pin next to it (Pin B). The web site shows the connector so that you can see what to do.)

Once you have shorted the pins together, turn on the ignition but do not start the car. You will see a light begin to flash the ECM trouble codes as explained on the web page. Write down the codes that the flashing lights provide and let us know what you found.

(If the CCM is faulty, that is a problem to troubleshoot because the CCM will only display codes on the LCD (Speedometer etc) display or on a scan tool. Since your speedometer display is not working, you will need a GM dealer to retrieve the codes from your CCM unless you know someone who has a GM Tech 1 Scan tool.)

One step at a time however. Check the fuses, get the ECM codes and post the results back here. Someone will try to help.

John

[c4c5specialist]

HI there,
I would be leaning towards a CCM on this one.
But checking the communications line is critical.
Allthebest, c4c5

[Tomas Portugal]

thank's a lot John. I'll tru it and i'll let you know.
Tomas, Portugal