Engine misfire codes - P0300 & P0304

[sdhow]

2010 Equinox with a 3.0 V6 VVT GDI...

I'm at my bitter end. First, the engine was out of the car to do a complete timing chain replacement; sprockets, phasers, tensioners, etc. All camshaft sensors and solenoids, coils, spark plugs, crankshaft position sensor, MAP sensor, throttle body, were replaced. Heads were removed to inspect valves for damage and a valve job done; everything cleaned including piston tops and valve stem seals replaced. Compression and Leakdown tests performed and verified that specs were close to (160 psi) as new.

After completed, engine threw code P0304. Pulled fuel rails and replaced all injectors on bank 2, replaced injector seals on bank 1. Still throws P0304 and occasionally P0300. Intermittently runs rough at idle, but not under load.

Took it to the GM dealer and they said it was a bad ECM. Put a new ECM in and programmed it...$1,200 later and they said "Oops, we were wrong..." They claimed there was fuel in the oil. Took the #4 injector to a shop with a test bench and they confirmed the injector is working fine, no leakage. After 2 weeks of sitting at the dealership, I had no confidence in their ability to diagnose the problem.

Could it be the high pressure fuel pump? I didn't think this could only affect one cylinder (#4) with a bad pump, but...

Thoughts???

 

[Dobruy]

Change injection #4, and check injector power wiring, at the entrance to the block

 

[sdhow]

Already done. That's not it.

 

[pipwax]

Check the coil pack connection wire for Continuity.

 

[Tico007]

When I was younger, I had a Toyota that was a heavy oil burner. Everybody said it’s just oil. Don’t worry about it. Well, one day I had a misfire. Went through all possibilities like you did. I finally gave up and sold it to the mechanic. He took it apart and told me it had a chipped valve from carbon in that cylinder heating up the valve and causing it not to seat correctly. Eventually cracking and scratching up the cylinder wallswith a little piece of metal.

So.. maybe it’s time to get a cheap endoscope or boroscope down into that cylinder and see what’s going on. Maybe it’s a chipped valve. Maybe it’s just a stuck ring and a piston soak can do something.

 

[sdhow]

Done that. Heads were off and valve job done to ensure no bent/damaged valves when timing chain broke...and chain on Bank #1 broke. No evidence of damage.

As I mentioned, it only misfires at low speed or idle...and intermittently. Machinist is pulling the Bank #2 camshaft cover and inspecting the lobes on cylinder #4.