1999 4.3 Sonoma Missing Under Acceleration

[frichardson1]

I've been through the scenic route on this one. Had the dredded P0300 code forever. Replaced everything prior to motor going out. Put new motor with 35 k miles and all seemed okay.

Now have an intermittent P0300 code that comes and goes. Engine idles fine and under normal highway driving. However, when I hit the throttle hard it misses like crazy, sound like the timming is retarted and only smooths out when I let off and then ease back into the throttle.

Feels like a lack of fuel might be the problem. Checked the fuel pressure before the motor swap at intial start and on highway and it seemed within specs. Anyone got any ideas?

Thanks

[old_master]

All P0300 series DTC's are usually caused by secondary ignition faults: Ignition coil, distributor cap, distributor rotor, spark plug wires, spark plugs.

Fuel pressure: GM does not publish any "engine running" fuel pressure specs, all tests are done with the engnie off. Make sure the fuel filter is not restricted. Ignition in RUN position, engine off, fuel pump running, pressure must be 60psi to 66psi. Pressure must remain above 55psi for 3 to 5 minutes after the fuel pump shuts off.

[2percent]

Sounds like ignition or plugs to me