2005 LS V6 missfire.

[james david]

I have an 05 LS V6 that is missfiring over 3500 RPM. Under 3500 the car runs fine and throws no codes, over 3500 I get P0300, P0301, P0302, and P0303.

I replaced the Plugs, coils, and wire harness to coil connectors.

I'm a a loss for what maybe causing this, but I remember reading somewhere that it maybe due to the timing chain tensioners?

I acts like the timing is not advancing, I can here the car backfiring out the intake at over 3500 RPM.

Help a fellow LS owner out, please, I bought this car for my daughter and she really needs it. Any insight yo can offer is appreciated, I'm really at a loss as to what needs fixed.

Sorry if the has already been covered, I'm new and didn't see it anywhere with a quick search.

 

[joegr]

Brand of coils?
Did you replace the IMRC o-rings?
PVC valve and elbow? Check for vacuum leaks? Fuel pressure?

 

[james david]

Cheap off brand coils, didn't replace o rings on intake, just put Indian head on them.

Not sure where the pvc is?

Does it have a Schrade value for the fuel pressure?

 

[joegr]

Cheap off brand coils...

That's probably the problem.

 

[james david]

That's probably the problem.

Could be, but it was doing the same thing before I replaced the coils, and it runs good below 3500 RPM, so I'm thinking it's something else, just rather not take the shotgun approach and start replacing things that won't fix the issue, more than I already have.