Hello,

I am new to this forum, i am a Porsche guy. But my uncle owns a 2001 Chevy Blazer. The check engine light came on, took it to advance, they said it had multiple Mis-Fire's. So from what i read it is usually the spider injector for this weird thing called CFI So i replaced the CFI with the new MFI spider which actually has individual injectors rather than the poppet valves.


So i got that done, started right up, drove it about 50 miles, then the check engine light came back on, and you could tell it was still mis-firing by the way it idled, not a bad mis-fire but still a misfire. So my uncle took it back up to advance, had them check it, scanner said it was Cylinder 1 misfire. Went home took out cylinder 1 spark plug, which was broke, replaced it, check engine light was still on. Then i took it back, then the scanner read a Multiple cylinder mis-fire again. My uncle had them clear the codes. but instead of the sensors resetting nothing is reading. We hooked it up to a more powerful scanner ( a snap-on scanner 15K). It says that nothing is reading, or resetting. We went through the drive cycles, many times. Still nothing.

Thank's in advance for the help.

 

Many things can cause P0300, however, it is almost always caused by a fault in secondary ignition, (plugs, distributor cap, rotor, plug wires, ignition coil). Plugs, cap & rotor need to be AC Delco on this vehicle, aftermarket stuff doesn't cut it. Checking fuel trims in the freeze frame snapshot will indicate whether the misfire was due to a lean or a rich condition. If the trims are negative, the problem is most likely ignition related. Worn distributor bushings and or drive gear, and incorrect camshaft retard will all cause negative trims. Low fuel pressure will cause positive fuel trims. If that's the case, check fuel pressure and leakdown at the service port, and at the fuel filter outlet.