Papikev252
Newbie
99 K3500 7.4L 454. I’ve been chasing this random misfire over a year. I’ve changed just about every sensor and part I can think of, I’ve also bought an Autel to view misfire counters and all sensors. The misfires only
start happening heavy when it’s warmed up and in closed loop. When I first start or drive above 1500 RPM, there are no longer misfire counters and it feels like it drives perfect. Here’s everything I’ve done so far: (not in this order)
At idle, warmed up.
start happening heavy when it’s warmed up and in closed loop. When I first start or drive above 1500 RPM, there are no longer misfire counters and it feels like it drives perfect. Here’s everything I’ve done so far: (not in this order)
- PCM
- Ignition module and coil (ACD and swapped with known good one to verify part was good)
- A malfunctioning mass airflow sensor
- A faulty crankshaft sensor
- verified ignition timing
- both front oxygen sensors
- distributor
- Smoked intake and exhaust, no leaks
- New EGR
- Verified fuel pressure(KOEO-60PSI, Running-52 PSI)
- Bosch fuel injectors
- Cap and Rotor (2x)
- Exhaust back pressure test to verify cats aren’t restricted
- spark plugs
- Both knock sensors
- Ran GM top engine cleaner through intake
- Both lower and upper intake gaskets (2x)
- IACV
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At idle, warmed up.
