Misfire / Running Lean

jwilson0341 · March 29, 2019

Ok..

2000 Chevy K3500 with 7.4.

Cylinders 3 & 5 misfire, rough run, often starts and idles fine - only OBD code is bank 1 running lean. Fuel trim on bank 1 was in the 25% range, long and short. MAP reading 38 pressure. Excessive fuel consumption, some white smoke on start up and fuel smell from tailpipe.

New distributor cap and rotor, replace bad O2 sensor bank 2, same result.All fluids gone through beforehand, no sign of anything mixing.

All cylinders compression dry/wet 160/180, cylinder 5 was 160/170, 3 was 155/165.

In process of replacing intake gasket, noticed cylinder 3 injector has already been replaced, different than the others, along with missing the middle retaining bolts. All injectors within resistance specs.

Cleaned MAF/ sensor, installed new plugs, lifetime wires good. My guess is MAP sensor doesn't hurt if its reading high, supposedly around 20 is the norm..before I put it all back together.

Any similar circumstances or ideas? Don't want to waste 500 or so on a set of injectors I don't need or keep Dis./Ass. the intake.

Logan Lanfear · April 1, 2019

Hows your fuel pressure?

jwilson0341 · April 8, 2019

50, 48 running. Steady.

Did the aformentioned work, ran great for a week. Obviously some of those were an issue. Today, damp outside, acted up again. Got a no start (no crank at all) after running a but and restarting. Reset computer (disconnect battery terminals/ touch), started up, still stuttering. It had given me this no start a few times before. PCM?

jwilson0341 · April 8, 2019

MAF? Unplugged while running, engine dies. Runs the same when plugged in or not. Voltage checked out, except the sensor wire dropped instead of climbing when i increased the throttle.

Dont know if its related, but the OBD disconnects half the time with a no-comm.

I'll try to check the grounds and fuel pressure again now that its stuttering.