2011 2500hd 6.0 misfire

[casey.mikl]

I have a 2011 Chevy 2500hd with 6.0. The truck has developed a misfire at idle and partially on the gas. I have replaced all the spark plugs, all 8 injectors, moved coil packs around, replaced MAF, MAP, b1s1 02 sensor (was getting codes for that sensor only), ECU, fresh gas and added cleaners, cleaned throttle body and swapped throttle body, had cats removed (already were blown out and empty) Nothing has solved the issue. Only bank 1 is misfiring. Mainly cyl 1 and 3. The truck backfires out the exhaust, and under load back fires out the intake. It will clear up like a switch flipped and run fine until the truck is shut off and restarted. I’m at a complete loss. By watching the snap on scanner. It appears as if it’s richen bank 1 and lean bank 2. I’m at a complete loss. It’s happening at idle and slightly off idle until it decides to clear up. I have been getting codes for random misfire and bank 1 sensor 1 02 sensor for heater issue.

 

 

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[riverbanks]

Thinking crank sensor?

[casey.mikl]

I was thinking possibly crank sensor or cam sensor but what doesn’t make sense to me is that it is only misfiring on bank 1 and not bank 2. And that it is fattening up bank 1 and lean out bank 2. Atleast the pulse width for the injectors is showing off on each bank. When it runs fine they are equal. If not they are off by a lot. Like 3.5-4.0 and 1.5-2.0


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[riverbanks]

?,that backfiring in intake,leads me towards crank sensor,one test is watch rpms on scanner and spray cool water on crank sensor,see if it changes anything, another is,move wiring a little for crank sensor,anywhere it's accessable,and safely

[casey.mikl]

I’ll have to try the spray on the sensor as that seems a little easier and safer. It will backfire through the intake under load. No load at idle it back fires out the tail pipe.


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[casey.mikl]

I haven’t done the test with the water. I had a spark plug that burned out (it had maybe 1500 miles on it) and I had to order a new set of plug wires for it. I’m gonna replace the plug and put new wires in it. I’m going to replace both up stream 02 sensors as well with new bungs. The threads on bank 1 are messed up and the sensor doesn’t seat fully into the pipe.


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[casey.mikl]

I replaced the bad spark plug today, along with all of the wires, the body to motor ground, and cleaned the main engine ground. I did notice that the wiring inside of the loom is rather brittle and corroded. I will be replacing the main ground from the battery to the engine. Here are some of the graphs that the scanner is showing. What I’m noticing is that bank 1 (side that always misfiring) 01 sensor number 1 is not nearly as “sensitive” as bank 2 sensor 1. Also fuel trims between the 2 sides seem to be off as well.




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[casey.mikl]

Okay. Little update if any one is able to help. I replaced the ground cable that was corroded. I checked for power and ground at all the sensors. When I use the sensor grounds, I get 8.70 volts with key on engine off. If I use the sensor positive and the ground of the motor, I get 12 volts. Where do the o2 sensors ground to? I have replaced the factory ground to the battery as well as firewall to rear head ground. Still no luck


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[94TBI]

Did you ever resolve this issue?

[casey.mikl]

6 hours ago, 94TBI said:

Did you ever resolve this issue?

No I have not. I have replaced grounds and cleaned ground points but cannot find the issue. I’m leading towards a wire in the harness or possibly corrosion within a ground wire somewhere. It’s driving me crazy. Recently I’ve had service trailer brake system and trailer wiring. The trailer brake relay was recently replaced and is new. So with the misfire, and now these other issues popping up I’m going to say a ground wire. The trouble is finding which one. I’ve replaced the battery ground cable, rear head tires body ground (which was previously blue and fell apart) and cleaned frame grounds under driver door. 

[casey.mikl]

Also to update, I did replace the crank sensor. No change. I’m going to try to replace both downstream o2 sensors. The one on the driver side looks like a universal one that you use butt connectors on. Maybe the downstream one is throwing the upstream off or something? Not sure being hopeful at the moment. I’m running out of options. Trying to get the issue resolved so I can sell the truck to get a full 4 door duramax. 

[shakenfake]

Downstream sensors do nothing.

[casey.mikl]

Yeah I know. It’s about the last effort unless I change out the whole wire harness. I have literally replaced every other sensor. Or I am going to take it to the dealer and pay for the diag and see what they come back with. I’m about out of ideas at this point. 

Edited October 4, 2021 by casey.mikl

[shakenfake]

Have you checked for compression and spark? Have you also used a noid light on the wiring harness to see if all the injectors are pulsing fuel? 

 

What codes are you getting? 

 

Maybe these are some dumb questions but just want to double check all the basics. I would also suggest take it to the dealer before throwing more parts at it.

[casey.mikl]

Yeah compression and spark is fine. I have not checked the injectors. When it’s in closed loop it misfires and runs terrible. When it’s in open loop it runs fine and has no issues. I have replaced maf, map, crank sensor, battery, all ground cables, injectors, plug wires, spark plugs, computer, o2 sensors upstream, cut out cats (starting to come apart). I’m going to take it to the dealer. I ran it today and running using the computer as ground I’m getting 14.6 volts. Also same on body and engine. I had a feeling it may have been a ground to ecu issue but it wasn’t.