Thread: Check engine light on and off constantly

I've got a '91 GST (Couldn't find a GSX when I had the money to blow.) Its got a new block, 16GT turbo, Evo3 o2 housing, 3" downpipe all the way back to the Apex'i N1 turbo muffler with an ATS silencer, tranny has bad syncros, new master cylinder, new ported throttle body. NGK Plugs & Wires, Greddy Turbo Timer. Nothing too out there.

Whats odd is that at about 1500 RPMs the check engine light turns off completely, and rarely comes on, when I hit 2500 to 6500 it sporadically turns on and off, and at about 2800 - 3500 its on almost constantly.

I know I'm not pushing the motor that hard, I'm still breaking it in. Motor has about 300 miles on it, and hasn't been totally hot-rodded yet.
I like to be nice for at least the first 500 miles or so.

Any ideas? I haven't been able to pull any codes from the ECU, and it has a new ECU as well. Forgot to mention that.

Thanks guys

Picked up a cheap datalogger cable, and am using some semi decent freeware datalogging software, and found the cause.

ECU is reporting it as the detonation sensor. Not sure why, its a brand spanking new knock sensor. Anyone have any ideas?
I'm sure I can safely clear it, the motor does report knock here and there. Its most likely because I've dumbed down everything so I can attempt to pass smog. Anyhoo, if you guys have any insight that'd help.

Thanks!

If its only that one code, then the reason its flickering is because of a connectivity problem. I would first take out the sensor and make sure its clean and clear of grease/oil since it sits between the axle and head. Also wouldn't hurt to spray the connector on the intake manifold bracket down with some electric cleaner. Though I've had a loose wire in the cabin before. It wouldn't hurt to double check your ECU harness, especially if there are current/previous taps for things such as an SAFC.

The jackass that I got it from had hacked the sh*t out of the harness, I've had to rework some things.

I'll definately double check the connector under the hood though. Thanks for the pointer. Every little bit helps with this bad boy.
Not a cheap car to jump into for my first import build for sure. So totally different than my old '71 F250, and the '68 Fire(chicken)bird.

Much funner car to drive too, course the truck was always a blast because no one had a clue that it had a build 390 small block in it. :)