LML Misfire/ rattle under high load

[clrussell]

Got an 11 Lml in the shop. Cp4 blew up a year or so ago. Cp3 swap and tuning got it going again (original injectors) cleaned all lines etc.

Always threw low rail under hard pulls. No big deal it's a grandpa truck.

Installed fass 95 two weeks ago as low rail was getting worse. Solved low rail (well bandaid) week later starts this misfire, shudder, rattle, smother out shit.

Well figure it's time for injectors. Brand new set from lds. Same problem.

Rail pressure and data look perfect. Changed tunes for giggles same thing.

It acts like it's getting fuel pulled away from it by something. Can't prove it. Truck will do it under medium load, hard load, brake torque in the shop. Always happens about 2300+ rpm.

Kinda lost on what to do with it. I havnt messed with the tcm any. Cannot see anything data wise that's a problem. I do have another 11 tcm on the shelf that had an intermittent problem for loss of power or something, so I'm tempted to plug it in.

Any ideas? Anyone have this issue?

 

[clrussell]

As a note. I can brake torque the truck in the shop and kill the engine if I don't let off the throttle fast enough while the problem occurs.

 

[Chevy1925]

have you tried swapping TCM's? remember, those are known to go bad on the 11 and 12 and cause weird stuff like this

 

[clrussell]

Tcm didn't change it

 

[IOWA LLY]

Replace the injector return line. It has that little pressure regulator built into it and that causes issues.


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[M.A.M.]

I've seen the regulator in the rail throw codes if it gets a little dirty. Clean em up, it's usually fine again...


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[clrussell]

I've seen the regulator in the rail throw codes if it gets a little dirty. Clean em up, it's usually fine again...


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Not a single code in this truck tho

 

[clrussell]

Pic of rail during problem. Made it do it for a solid 30 ...

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[Chevy1925]

who tuned this? that looks like a regulator issue and the LML is very picky about getting the cp3 voltage correct.

 

[clrussell]

who tuned this? that looks like a regulator issue and the LML is very picky about getting the cp3 voltage correct.

Very well known tuner.

Truck drove fine for basically a year with the same tune.

 

[clrussell]

http://www.duramaxdiesels.com/forum/archive/index.php/t-35546.html


I'm starting to see why the return side could be a problem

 

[Chevy1925]

Very well known tuner.



Truck drove fine for basically a year with the same tune.

No, throwing that 0087 code is not “drive fine for a year” lol.

Think you are on to it though

 

[clrussell]

No, throwing that 0087 code is not “drive fine for a year” lol.

Think you are on to it though

Realatively fine

 

[clrussell]

Upon further watching something is telling it to drop mpa about 5-10 mpa when problem occurs.

Ordered a return line kit for it, and going to clean the rail regulator while I'm there

 

[torqued2dmax]

clrussell Ive seen you work thru some amazingly difficult problems ! With all the idiosyncrasies that all the different year trucks have , it is amazing that you all can keep it straight ! I can barely keep up with just LLYs ! Keep up with the great posts , thanks !

 

[clrussell]

Installed new return line set up today and truck seems good to go. Pulled regulator and cleaned even tough it looked brand New while I was there

 

[M.A.M.]

Bet your glad to have that thing out of the shop. Glad it worked out!


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[RickyG491]

Thanks a bunch for the info! Had a 2015 LML with a blown CP4 that I did a CP3 conversion with the exact problem and thanks to your advice I was finally able to fix it. Signed up for this forum just to personally thank yall. This job was a major headache.