wjm2002Chevy

Random Multiple Cylinder Misfire Trouble

Already Replaced:
Plug & Wires
Mass Air Flow Sensor
Cam Position Sensor
Crankshaft Position Sensor
and checked for vacuum leaks..

Before replacing all this i had a lean code and the multiple misfire code (PO 0300)..now it just has a misfire code (PO 0300) and still a bad skip...
seems to be worse when cold. Please help, i've been banging my head against the wall with this one!

country_09

Checks cats and o2 sensors?

MDTAHOE

If it a flex fuel engine (Z engine code)? If so replace the intake gaskets. Very common and is always worse cold.

wjm2002Chevy

Wouldn't the O2 sensors show a trouble code if there was a problem with them?? Can I test them without replacing them first??

wjm2002Chevy

Not a flex fuel engine, (engine code "T")
Will try the O2 sensors this weekend.. Is there a way to test them??

EinST

The PCM will usually detect anomalous O2 sensor readings and set a trouble code. However, an O2 sensor can go out of calibration (hard to test for that) or an exhaust leak can affect its measurements (oxygen content inside the exhaust pipe vs. outside). If you have anything aftermarket in the intake or exhaust system, or PCM tune, start your troubleshooting there.

wjm2002Chevy

All factory equipment, just did a fuel pressure test and getting 46-48 lbs. Is that enough??

EinST

If you've measured it with key on, engine off, it should be 55-62 psi. If so, suspect the fuel pump or fuel pressure regulator. If you can raise the pressure by repeatedly priming the fuel system (turn the key on, wait a few until the fuel pump cuts out, turn the key off for a few, and then repeat), it'll usually mean a fuel pump on its way out. Note "usually" rather than "always."

wjm2002Chevy

Ok, today out of desperation i changed the intake gasket because someone at the parts store told me they had a similar problem and that fixed there truck so i went for it and STILL NO FIX Grrrr...
Did another fuel pressure test and with the key on and the engine OFF ive got 50-52 lbs but with the engine running its about 47 lbs. What do you think??

MDTAHOE

When you replaced the crank sensor, how did you do the relearn?