lmm fuel knock misfire

[mamu]

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.

thanks

[Chevy1925]

put the stock tune in it and see if the knock stops. it will still start and rev without the emissions crap hooked up on a stock tune

[cdbright]

my old LMM did that when i hooked up the fuel pressure gauge just FYI , any Autometer fuel 0-30K would do it

[cdbright]

rail pressure

[mamu]

put truck back to stock. same thing.

truck will rev but it misses and shakes all the way through the rpm range.

checked rail pressure and it shows to be matched pretty consistent with desired.

[Chevy1925]

time to start looking at a broke crank then

[stibuilder]

Program the injector codes on all the injectors you replaced its the 13 digit number.

[mamu]

yea we reprogrammed all the injectors. had 2 that wouldn't program. figured out they where plugged in wrong (4 an 6 was swapped) but all programming is done now.

a broke crank? this don't act like any other broke crank I've seen but ill check today and see.

[mamu]

checked crank. cant see any signs that its broke. turned it from front and read and theres not any play. it idles smooth now. but as soon as you get to the 925 rpm it goes crazy. I honestly have never seen this so I'm sure theres a sign somewhere I'm overlooking.

[mamu]

any one?

[Burn Down]

Are you able to monitor the crank and cam sensors when it starts running rough?

[mamu]

thats the only thing i haven't watched specific. like the cam ring came loose. but the rpm doesn't change when its acting dumb at idle. hard to tell. ill check the cam counts missed in the morning tho.

[mamu]

with truck running and missing it doesn't count any on the cam reference missed. but when i crank it up it will count to 33-35 before it starts and runs. but never goes back to 0 while running. but never goes up either.

still showing #1 cylinder misfire.

[Burn Down]

With the 1 misfire I’m still betting you have harness issue, maybe ecm... how did you test the wiring?

[mamumtsllc]

Originally Posted by Burn Down

With the 1 misfire I’m still betting you have harness issue, maybe ecm... how did you test the wiring?

I've changed ecm and it stays. I load tested all wires and checked resistance. Made sure they weren't rubbed together and jumping fire. I'll check them again to make sure.

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