1990 Chevy Truck stumbling at 1/3 throttle and loss of powe

SSBREAKDWN

MEMBER
1990 CHEVROLET TRUCK
6 CYL
4WD
MANUAL
196,000 MILES

I replaced my 4.3 engine a few months ago. The engine I installed is a freshened engine. All new Gaskets, seals, oil pump, timing chain, cleaned and reinstalled all components. Ever since the truck has had a stumbling and loss of power issue. The plugs, wires, cap and rotor have all been replaced. Along with the throttle position sensor and fuel filter. I have checked all the vaccum lines for leaks with no luck. The truck idles ok, a slight rise and fall of rpm but nothing major. The throttle body gasket has been inspected and replaced. The plugs are white and don't show signs of oil or fouling. When sitting at red light the engine seems to load up a little and blows some smoke when pulling out. I figured that is from the new oil pump and old rings. I had the timing set to factory specs. I am getting ready to replace the EGR valve and Air control motor, but i'm tired of spending all this money replacing things that aren't bad. Any idea whats wrong?

Thanks, Rob

1 Reply

CARADIODOC

MECHANIC
33,916 POSTS

Fuel delivery is based on air flowing into the engine. That is measured by the Mass Air Flow (MAF) sensor and MAP sensor. Any air that leaks into the air intake system and bypasses the MAF sensor will not be measured and the corresponding fuel will not be delivered by the injectors. If the MAF sensing element is dirty, it won't measure the proper amount of incoming air.

The MAP sensor is used to read barometric pressure. If the reading is not correct, fuel metering won't be either. If the MAF fails, the MAP is used as a backup measurement but it is not as accurate.

Caradiodoc