2005 Silverado 3500 6.0

I’m thinking possibly a crank sensor issue. P0300 see #1 plug wire arcing on exhaust. Put new plug wires and plugs on runs good at idle. The misfire counter is acting funny. I’ll unplug cyl 2 coil and it’ll count on cyl 2 and 7. Those are the 2 cylinders that count up on a load. Swapped coils. Flow tested injectors all the same. Performed crank relearn. Out of ideas. Vacuum gauge nice and steady even when misfiring. Had to diagnose a no communication with any module before to even look at live data has a rotted airbag module. Unplug 1 cylinder to test the accuracy of the counter it’ll always be in accurate. Any ideas??

Maybe use an amp clamp on the coil fuses with an ignition sync to see if timing is changing on #2 or #7 when the miss is occuring? One coil getting fielded too little/too much or just flat not occuring should stand out like a sore thumb.

It just so happens I ran into my first failed 6.0L crank sensor last week. :lol: Tach wouldn't operate most of the time, long crank. Green is the CMP, yellow is the CKP. There should have been 58 teeth in the CKP waveform...

Seen an odd thing maf read 9.5 gps at 2500 rpm driving. Fuel trims pegged. Cleaned maf no help. What do you mean if timing is changing? My amp clamp got leant out but broke in a fan. I had 4 channels going to cyl 7 coil all looked good. Also scoped injector. What would cause misfire status to change from normal to inactive I think it said

Cheryl wrote: What do you mean if timing is changing? My amp clamp got leant out but broke in a fan. I had 4 channels going to cyl 7 coil all looked good. Also scoped injector.

I was thinking if there was something wrong with the CKP that was causing the dwell time for the #2 or #7 coil to change. Seems unlikely, I know, but you've eliminated all the easy stuff. :lol:

You've probably thought of a broken valve spring? I know the vacuum gauge didn't twitch. It might be worth comparing running compression to another cylinder.

I’ve never actually checked a crank sensor for a misfire on a cylinder. Do you think a misfire shows up on a crank waveform just asking. I’ll do a running compression test on the cylinders and just see. Vacuum gauge your was 20 inches solid but never hurts to try what others suggest. I got another amp clamp ordered. Going to watch fuel injectors and coils. I thought the injector and arcing plug wire would fixit. The #7 injector flowed about 5 psi less

Oh really? :huh: Maybe try moving the injector? Or a secondary probe on the #7 coil wire to check for a lean miss?

I replaced number 7 injector and scoped control on it I never lose control. Going to current ramp the coils and injectors when I get a new amp clamp. Definitely doing a volumetric efficiency test due to low maf g/s readings I was seeing plus throwing a p0101 now

Update performed volumetric efficiency test with original maf sensor only hit 175 grams per second at 5567 rpm 67 degrees iat. New maf hit 230 grams per second at 5600 rpm same temp. Still a little low.

Yeah I got 68% with your new MAF. I know that OHV engines never make amazing VE numbers, but you'd think this one could do better.

I have a known good capture from an '06 Silverado 6.0L, and it maxed out at 263 g/s. That gets the VE to 77%, which I can live with.



Still flags a miss on #7?

Yep intermittent missing on cyl 7

Swapped plug coils from cylinder 2 and 7 to different cylinders on the engine. What’s weird I think is the control wire for the coils 2 and 7 are only 4 volt square waves I think there supposed to be 5 volt turn on signals. Even when not missing that’s what they show

New injector on 7 scoped injector never dropped out.

I’m probably going to do an exhaust back pressure test on both banks. Then check the intake system for restrictions. You know how to check the intake side besides just checking the air filter and intake boot up to the throttle body?? Do you know if these engines are known to get out of time? I’m going to scope cam crank sensors to see if timing is off. This is a roofing truck for a company this thing is beat....

Easiest way I know of to check for intake restrictions is to watch the MAP at WOT. It should read barometric pressure, or maybe 1 inHg below. Much more and there may be an issue.

You can also sometimes find restricted exhaust by watching the upstream O2's during WOT. If one side truly is restricted, the OTHER side will show lean at wide open. The restricted side will show full rich.

I knew about the rich and lean o2 tests during exhaust back pressure testing. Didn’t know about the map reading for intake restriction testing though. Think I might figured this out. Cylinder 3 ignition coil connector pin figment was intermittently making contact. Runs good now but the transmission slips