Tykho

Hello all,

Looking for some advice/troubleshooting ideas with my 99 FRC. Car currently has just over 70k miles on it. Anyway, I got some XS Power longtube put on the car by a local shop around 3 months ago. At first all seemed fine with the car, but the headers torched through a plug wire on a trip to Nebraska from Colorado, and shortly after, I've had this persistent electrical problem.

Basically, I start to get wild gauge bouncing on the speedo and tach, and when I had a scanner plugged into the car, it also seems to be missing on 5-6 cylinders when WOT. The car is still driveable, and the problem is intermittent, and seems to happen more often immediately when I go WOT. I have no consistent codes that are thrown, except I do get a Loss of Communication with the EBCM, which comes back when the car is turned off/on after the issue starts. I have also had the right side fuel injector rail fuse blow twice in the last 1000ish miles, but I'm not sure if that's a symptom of the same problem.

I have tried to do a lot of research and troubleshooting on my own before posting here, but I'm at a loss. All of the grounds have been checked, and cleaned, and some have even been reterminated. These include the block grounds, battery ground strap, front two chassis grounds, door accordion grounds, and ground by the starter. I have also replaced the plugs, wires, and tested another set of coil packs. The alternator and battery have tested good. I have also yanked out the star plugs in the cabin, and that also did not keep the issue from happening.

I realize the modules kind of communicate in a round-about fashion through the SDM on the pre-01s, and I really hope my EBCM is not causing the issue since absfixer is not an option. Really hoping you guys can maybe help me find some other cause.

Anyway, thanks for reading, and thank you in advance for any advice.

69

A Couple of threads to help your troubleshooting.

Perform a detailed visual inspection on the injector wire harness in the area posted in the photos on this thread http://forums.corvetteforum.com/c5-t...verything.html

https://www.corvetteforum.com/forums...g-harness.html

https://www.corvetteforum.com/forums...s-popping.html

Bill Curlee

The BCM is the key module as all modules communicte with the BCM.

That being said, please read and post ALL your DTCs. IF,,,, there are a crap load of old history DTCs that make diagnosis difficult,,, PLEASE clear ALL the DTCs and take the car for a drive. Then read and post what comes back.

The serial data buss is very sensitive to corrupt data and bad serial data signals.

To the left of the BCM are two thin connectors. Find the one with FOUR wires and pop the TOP off that connector. See if that clears up your issue. Removing the top isolates the LDCM, RDCM and SCM from the rest of the modules serial data lines.

The LDCM, RDCM and SCM will show NO COMMS with that connector apart.

Bill

Bill

Tykho

Thank you 69 and Bill, I will check that out and post my codes when I get home, I'm unfortunately out of town until Saturday. There were a ton of codes after the issue first occured, but I have been getting the loss of comm consistently. I appreciate the help!

dadaroo

Here is what the 2 serial bus connectors look like that Bill described.