I am helping a friend diagnose a misfire over the telephone on a 2000 model chevy truck.
Its giving a p0300b code and every revolution on 3&4 it misfires. Plugs were checked and changed and the coils and wires were moved and it didn't affect it. I suggested he check the ltft to see if it might be a clogged convertor, he checked and at idle it was 5.5 bank 1 and 7.2 bank 2. all the injectors are working correctly and he says the maf was showing frequency but couldn't tell me what exactly it was before i had to jump off the phone.

Next idea i had was a crank and cam relearn along with a flash of the pcm from the dealer???? What do you guys suggest?

 

oh and you can rev the truck to 1500 rpm and it stops the misfire!

 

when you find out...LET ME KNOW!!!! its driving me iNsAnE on my 2000 silverado...i was told i should check the O2's but mine are doing the same thing your friends are, working fine that is.

 

Is the truck in question stock or modded? Cam?...tuning for cam? How does he know that the injectors are working as they should? Just because their being commanded doesn't mean that their doing their job (not saying that an injector is the problem, especially since the misfire only seems to be at idle, just curious how they checked the injectors).

Vacuum leak? Tell him to try spraying some carb or intake cleaner around the intake ports and whatnot and see if the idle and AF readings change when doing so...

 

i had a 2000 that would miss bad on 3 and 4 at idle... BAD i thought it was low compression.. but it ended up being the fuel pressure regulator was shot

 

Hmm, that's cool, and an easy fix...pull the hose and see if fuel comes out...