1998 tahoe misfire / no power high rpm's at full throttle

[Bigbody250]

This issue has me kind of confused.... No CEL's and runs great up to 3/4 throttle. When going full throttle it feels as though timing is extremely retarded. The motor loses power and will slightly miss. Can go 3/4 throttle holding each gear up to 5 grand with no issues. New cap and rotor, plugs, fuel filter and fairly new wires.

I'm not sure if it's a fueling issue or possibly related to an exhaust leak. Fixing the leak this weekend, have been working too much. Could it possibly be the spider or fuel pump crapping out at high flow? Probably 1 out of 10 cold starts it takes a second to build fuel pressure to start. Normally just turns over and I'll cycle the key and will start just fine.

Any help would be appreciated. Have tools in the truck but out of town at the moment so really didn't want to have to change the spider or drop the fuel tank out without being at my house.

 

[SunlitComet]

just have your fuel pressure checked at various stages of engine operation and have the shop do a injector balance test. if it is a fuel problem it will show up on those tests. exhaust leak does not cause power loss.

 

[Bigbody250]

Was thinking exhaust leak might be throwing the o2's off because it's at the manifold collector

 

[gpracer1]

Was thinking exhaust leak might be throwing the o2's off because it's at the manifold collector

O2s are not used by the PCM at full throttle.
Therefore if it runs good at part throttle the O2s are probably good. Mods will however affect full throttle without a tune, as will low fuel pressure, etc.

If you do have a leak at the collector, you should fix it first for sure since the PCM will have stored possible bad O2 data.

 

[Bigbody250]

No mods besides exhaust and k&n filter... Just ordered a fuel pump off eBay. Seller had good ratings and it was only $60 vs 200 everywhere else. Figured I'll need one on hand anyways... Need to do the spider eventually but haven't had the random misfire that you normally see when it goes bad.

Hopefully I can find the collector gasket local tomorrow and reset the computer to see what that does.