Duramax Diesels Forum Truck of the Week
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Old 01-02-2018, 09:18 AM
mamu's Avatar
mamu mamu is offline
Join Date: Mar 2010
Location: arkansas
Posts: 142

Default lmm fuel knock misfire

hey guys,

i had a lmm come in with a fuel knock and bucking and jumping on the road. reduced engine power and barely would pull it self. showed 3 and 5 cylinder misfire on the computer but that was the only codes. heres what I've checked.

crank ring good and tight.
load tested and ohm tested all injector wires from ecm to injectors
swapped ecm and didn't change.
ran compression (all 375-400ish)
pulled injectors and had them tested...replaced 3

put it all back together and now 4 and 6 show misfire codes. at idle its smooth and fine but when you crack the throttle at about 925 rpm it starts knocking and missing. i can cut out #1 injector with the scanner and the fuel knock goes away. but it still misses.

all balance rates are -2.5 to +2.5 are the 2 worse the rest are -1 to +1

truck has whiteish blue smoke. smells like fuel. but honestly i don't have a clue. im to the point where i need anybodys thoughts and see if we can't stumble across the issue.

truck is 08 lmm 2500 crew cab. deleted with ppe. has been that way for over a year. rite before christmas this issue started. no other mods that i know of.

2006 cc dually efi studs danville 2.5 drop in built trans fass
2005 ecsb efi ppe trans airdog 150 batmo
2007 crew cab dually ppe hot +2……stock.....sold
2002 rclb efi airdog 150……shop truck
1992 rcsb 6.0/nv4500 efi by black bear 9.25/11.5 solid axle conversion 37'' boggers (weekend warrior)

Last edited by mamu; 01-02-2018 at 09:20 AM. Reason: forgot truck mods
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