Crossfire event , coil near plug

Jeff Owner/Technician Flesherton, Ontario Posted   Latest  
2001 GMC Sierra 2500 HD SL 6.0L (U) 4-spd (4L80-E)
Ignition Timing

The is a performance set up on this LS engine . 408 cid stroked . Running a Holley EFI stand alone unit . 

The truck coughs up the intake and pops out the exhaust as Soon as the throttle is opened . Crank and cam signal present and in sink , I have checkedthe static timing with a timing light and it is correct . Holley doesn’t not believe it’s a faulty ECM but don’t have any ideas as to why it’s happening . has Any one been down this road before . Thanks in advance .

also steady compression at 185 on all cylinders . Swaed plugs wires and coils no chance . To me the ecm is firing the wrong cylinder at the wrong time . 

Also this unit ran great for 2 weeks and then developed this problem . 

Dave Mobile Technician
Ironton, Ohio
Dave Default

Sounds like a lean condition. I hate modified vehicles.

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Scott Manager
Claremont, California
Scott Default

Hi Jeff, I agree with Dave’s assumption that it’s lean. Have you verified that the fuel pressure is set to spec? Pull a fuel sample while you‘re there. Do you have the software to interface with this system? Perhaps there’s a fault? Can you verify KOEO MAP? Not sure which system you have but I’ve tuned many of these on a chassis dyno and a wide band sensor. Many moons ago, I used to turn…

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Jeff Owner/Technician
Flesherton, Ontario
Jeff Default

thank you for your input , I have checked the fuel pressure and air fuel ratio during this issue . air fuel hangs out 16-17:1 fuel pressure stays were it has been set at 43 psi . I was blaming the lean air fuel mixture on the misfire event . I loaded a tune for open loop status only so it would never go into fuel control and it run off a base fuel calculations [ no change ] . what I have learned…

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Jim Mobile Technician
Southampton, Pennsylvania
Jim Default

Jeff. I agree with what others are telling you, it does sound like it is a Lean Misfire. My suggestion would be to connect a Propane enrichment bottle up to the intake somewhere, then as you begin to open the throttle also give it a shot of propane. I have been using this method for years to isolate the exact cause of the misfire, this way, if it still misfires you need to move on to another…

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Jeff Owner/Technician
Flesherton, Ontario
Jeff Default

Thank you for your input I will be sure to try the propane jim . If you dont mind explaining , how does a lean air fuel mixture cause coughing up a intake ? I have never been tought this yet and have not seen the issue before . Of coarse I like to know the deep theory of what is happening in the cylinder . Thank you !

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Richard Technician
Virginia Beach, Virginia
Richard Default

16 to 17 AFR is too lean. You might want to use a mityvac flow tester or some clear tube to make sure the fuel isn’t aerated . HTH.

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