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I have a 2007 Chevy Aveo 1.6l that is kicking my ass. Originally, it came in due to a bad head gasket causing coolant intrusion into the cylinders and smoking. Fixed that issue and came back a month later with a p0300 random misfire code.
The vehicle misfires at idle only as can be seen on the misfire counter, all cylinders misfire randomly but the misfires cannot be felt. Sometimes its one or two cylinders misfiring more than the others but it tends to be completely random.
Things I have done, disconnected battery overnight and performed crank relearn, new spark plugs, wires and coil. Compression okay on all cylinders (150-175psi).Fuel pressure 60 psi, alcohol content 5% and condition seems good (clean and clear). Fuel trims okay at nearly 0% most of the time, smoke tested intake system and found leak at egr tube but replaced and issue still there.Verified timing and it is spot on, no variable timing on this engine.
What am I missing? What other tests should i do next?
I would want to use a Pico scope to record the crank signal and use a frequency math channel to verify the crank speed is indeed slowing down due to misfires.
Some of these older ones only respond to a Tech2 performing the Idle Re-Learn.
I used an Autel Ultra to perform the crank relearn. Do you have any links to videos where I can watch this scope testing method performed? I am okay at the basics of scoping but math channels are above my skill level and knowledge at the moment.
I've had my Autel, Launch, Thinktool all let me down on Older GM crank relearns. Must be a Chinese software thing. These tools have thier place though. But a factory tool can't be beat.
Will definitely look into this, so if the crank speed is not slowing down at the time of the "misfires" that would determine the engine really is not misfiring and something else is causing these false misfires? I should probably add, the engine mounts seem to be causing some vibrations and also the belt tensioner is rattling and making noise. Can something like that cause "misfires" to be detected?
By 2007 GM's algorithm for misfires is pretty good. I've seen driveline components set misfires off. Any Resistance to the crankshaft can set off a misfire. Unbalanced parts are the usual culprit. Ive seen vehicles with TCC problems, CV Axles set misfires.
For the PCM to think there is a misfire there has to be a slow down in crank speed.
Engine mount vibration that is excessive can trigger knock sensors to not advance timing as RPM is increased, causing misfires.
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