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I have a 2004 Chevrolet Silverado 2500HD 6.0 with 225,000 miles and some strange misfires and I’m seriously stumped on this one. This is the issue: when the truck is parked and in idle cylinder 1 Misfires maybe 1-30 times per cycle. Once you rev it high it gets much worse. Like 200 times per cycle then the cycle counter recounts and it continues. And the engine is actually misfiring because you feel it. This is the strange part if I brake torque the engine all the misfires on cylinder 1 and All the slight misfires on the other cylinders immediately drop to 0. And the truck is smooth.
This is what I have done so far to the truck:
New timing chain
New oil pump
New knock sensors
New acdelco plugs
New spark plug wires
New Upper Intake gasket
All new injectors
Cleaned the mass airflow sensor and new air filter
First thing I did was swap 1 and 3 coil pack and plug and wire. Misfire stayed on cylinder 1.
Swapped injector 1 and 3. Misfire stayed with cylinder 1. Put an amp probe in line on the power side of cylinder 1 and current was higher than the others so I was sure it was a stuck open injector. But after adding new injectors to all 8 cylinders the misfire is still there on cylinder 1. I also load tested cylinder 1 at the connector and voltage stayed steady at 14.3 volts.
Second thing I did was tighten spark plug gap from .040 to .030. No change.
Poured water all over engine trying to see if there is any vacuum leaks. Engine never stumbled enough for concern.
Flooded the engine with propane around every area where there could be a vacuum leak while watching O2 sensors voltage to go high and stay high. Never revealed anything. Pour propane straight into mass airflow and it immediately read it and ECU pulled fuel back like it should. Take it away and it started to add fuel like it should. O2 sensors read voltage like it should.
Third thing I did a leak down test on cylinder 1. Put 80 psi in and it dropped to 74-76. Which isn’t bad at all. Not enough to cause misfires like this.
Fuel pressure is a solid 62 psi at idle and when you rev it high. Did a injector balance test before I changed the injectors and all of them had the same pressure drop just like they should.
Only thing I haven’t done is look at spark waveforms and injector waveforms. Maybe that’s where I should head next. Just can’t wrap my head around the fact that it misfires only in park at idle and when you rev it high. Under load absolutely no misfires. None whatsoever.
Also, truck does have a rear main seal leak. But not sure if that would cause this issue.
If there is anything else you guys could think that I could do please let me know.
Last edit: 3 years 2 days ago by davidgrisanti. Reason: Added something else
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