97 Vortec V8 loss of power at 4k RPM

97 SS 383 · October 8, 2002

Hey all,

I have a truck with a 383ci Vortec engine that ran fine for a few months, but for some reason loses almost all power at around 4200 RPM now. It just falls off. I have checked the fuel pressure, and it never falls off, I have bypassed my MSD module, tried a different coil and coil module, and replaced the cap and rotor. Anyone ever heard of this before or have any other ideas of where to check? It makes an obnoxious noise through the itnake (I think) and I can watch the MAF readings go haywire when this happens. As soon as it shifts, it runs fine until it gets to that RPM range again. Any help would be appreciated.

MarkD · October 8, 2002

Is it a custom engine or a GMPP engine?

If it is a GMPP, I would investigate the MAF, maybe switch it out and see if the problem goes away.

Try unhooking the battery for 30 minutes or so, then try it again.

If it is a custom built motor, quite a few people have been having Valve spring problems lately. You could be having a valve spring float problem.

97 SS 383 · October 8, 2002

At this point, nothin in the engine but the intake and block is GM. The heads are edelbrock Etec-200's, the cam is custom ground for the engine. the MAF seems to be reading correctly, it is reading the air going crazy when whatever hapens is happening.

What would cause a valve float problem when he engine ran fine for the 2 months or so that it did? I was thinking of that, but wouldn't I have chewed up a piston or valve by now if that were the case?