1996 GMC Sierra Engine stumbles

HVGERG

MEMBER
1996 GMC SIERRA

Engine Performance problem
1996 GMC Sierra V8 Four Wheel Drive Automatic 198.76 miles

The engine stumbles when rpm get to around 3100. Also sometime hard to start, like it tries to run on half the cylinders and finaly will run on all. Fuel pressure is 52psi, fluxulaty exhaust back pressure of 0 to 1 lb, new cap, rotor, plug wires, spark plugs, fuel filter, new mass air flow sensor has been tried, new knock sensor, timing adjusted and engine vaccum at 18 in. Engine code show lean at both front oxygen sensors, no miss fires and pop back through intake and exhaust. The mechanic looking at it is thinking maybe crankshaft sensor.

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

Hi hvgerg, Welcome to 2carpros and TY for the donation. Be advised this is not an easy fix troubshooting/testing has to be performed to get to the root of the problem not guessing or throwing parts at it-

Could be the crankshaft positoning sensor and also one of the following listed below,

Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking, fuel filter or defective fuel pump.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note:If it doesn't apply disregard meaning if it doesn't come with one ignore it and keep testing