derekderek

iTrader: (21)

I am trying to track down a misfire at first it was throwing code p0300 multi misfire I readjusted the valves and it seemed to help for a little bit. But now it is throwing p0303 sometimes and p0304 sometimes just randomly. I will erase codes and it will throw one of those codes but never both.

I have all new ignition tried swapping plugs wires around nothing unplugged o2's one at a time and both that doesnt help. Does it when its first cranked throws codes within a min. Weather or not the engine is hot or cold. I noticed my knock sensor was cracked and barely connected would that cause the codes and for it to be down on power? Also has new injectors flow matched and everything good fuel pressure. What else could be causing this. I am stumped thanks for the help.


Derek

ss.slp.ls1

iTrader: (36)

What exactly do you mean you have an all new ignition?

I would try to watch the wires at night and look and listen for arcing. Especially on wires #3 & #4.

derekderek

iTrader: (21)

New Opti new cap and rotor, MSD coil, Taylor wires, new plugs. I tried different wires and it still throws the same code the only thing untouched is the ICM I wonder if that would cause it?

What about the broken knock sensor would that make the computer think there is misfires or anything?

ss.slp.ls1

iTrader: (36)

I think a faulty knock sensor would cause excessive knock retard, don't know if that's enough to cause a misfire or not though. From what I have seen and experienced, a faulty ICM causes an all-or-nothing problem, not a cylinder specific problem. But it can't hurt to get it tested.
What brand opti? What brand cap and rotor?

derekderek

iTrader: (21)

The cap and rotor are ac Delco. Well changed the knock sensor swapped wires again checked at night for arching and all is good. I guess next thing to look for is bad grounds maybe a compression check? The car sat for almost 2 yrs in storage before I did all this maintenance on it.


I checked pretty much all that I could think of I even pulled the plug and it looks like it is firing good. Could it be false readings the computer is picking up? How does the computer determine a misfire? I pull the plug wire off and the engine starts shaking and missing plug it back in its fine same for that injector. Any ideas would be helpful and welcome. I am at a loss.

derekderek

iTrader: (21)

Just figured I would give an update on my problem. I did tons of searching on here and there was alot of threads that just died out no solutions to them so I figured I would post up my solution.

Well like I say I was searching on here trying everything in the world people had suggested but nothing worked. Compression was good I knew all ignition was good fuel pressure everything you could check I did. Well this started after I did a header swap so I went back to basics pulling plugs looking for a crack in the spark plug or a burnt wire. Well during this process I noticed something odd with my plug wires. So I break out my Chilton manual and sure enough plug wires 4&6 where crossed So I swapped them started it up and sure enough runs smooth as can be now.

I am glad I didnt start throwing money at it replacing stuff. For something stupid like that just goes to show you sometimes the simple things that you know you cant get wrong can some times be wrong. Thanks for all the help


Derek

ss.slp.ls1

iTrader: (36)

Yep, basics first.
Glad to see you got it figured out man.

derekderek

iTrader: (21)

Thing I dont get is why it was throwing a P0303 cylinder 3 misfire when it was cylinders 4&6 . I would still like to know how the computer determines a misfire just for my knowledge.

ss.slp.ls1

iTrader: (36)

Seeing as you have a OBDII, I know that the crankshaft position sensor helps detect misfires, but I don't know what else it uses.