Help Please! Can Not Solve, 4-cylinder misfire fault

[serkanur]

Hptuners has a crank relearn function in the scanner you can give that a try and see if it clears it up ... if the crank shaft variation calibration is not properly learned it can give false misfire counts

Thank You for your post.
I'm using my friend's cable.I don't have it right now.I will take it.And try it
I am not sure Our car has a crank relearn?
Anybody have know 2.0 LNF has a crank relearn ?

[TCSS07]

Ohhh right the lnf you dont get to much on the scanner to do ... do you feel the misfires - I've had o2 sensors cause misfired also

[ZeroBoostBuick]

Have your friend hook up the scanner and in up top in the scanner between the play and engine icons is what looks like a power button. That's the "Vehicle Control & Special Functions". The crank re-learn should be in there.

If the scanner doesn't have the crank re-learn function for your car, then the car dealer mechanic can do it for you.

[Jay@HAP]

First thing I thought of was a loose valve seat.

I know you did a compression test, but if you haven't you need to do a dynamic/running compression test. A cranking compression test just tells you if the cylinder is sealed. A dynamic compression test will show you what's going on the cylinder with everything moving. I normally do this with a scope and a pressure transducer in the spark plug hole.

You can have a weak/broken valve springs and with a cranking comp test it will show good, but with a dynamic test it will be quite obvious because the cylinder pressure will be lower.

[cobaltssoverbooster]

You need to check for any rubbing of metallic components that are bolted to the motor.
Solid motor mounts make knock sensors go crazy, so if you have those then your sensors are useless. i had John Powell's solid mounts and ended up disabling mine and using a set of knock ears from link ecu to monitor knock manually by ear and by adjustable sensitivity. Same goes into effect for balance shaft deletes because you will have no counter to low rpm vibrations.
Your chassis wasn't mentioned so if you have a kappa chassis they typically had a floating clutch pack which is prone to rattling under certain conditions thus causing sensor triggering. if it always happens at a certain load spot and running race fuel doesn't make the knock go away then its likely a loaded condition mechanically triggered event.
you could try clocking your knock sensors to the manual which iirc is to torque them down with the harness horizontal to the engine and pointing to the rear of the engine. a few years ago GMTech, MikeM, CodenameBilldoe, and myself tested clocking and saw temporary results which leads us to believe in any position the contact of the sensor to the block is good enough to not induce errors. It is wise to check sensor torque and to inspect for corrosion on cars where salt is thrown for snow.
the number one thing that shows kr, and more specifically false kr, is the smoothness of your tables and how well you have the pid, optimum spark, and main ignition maps calibrated. the lnf is a sensitive computer and having everything dialed in properly goes a long ways.