What on earth is wrong with this LMM?

[Boost]

All along I was thinking that I may eventually help this guy out with EFILive, his truck keeps going into limp mode because of his mods. But he says that the modifications are minor and the truck is a lemon. Here is the thread from the diesel forum, where I am 4rotorcorvette. I would like to learn as much as possible about the LMM and it's problems to prepare myself in case I have to get involved.

http://www.dieselplace.com/forum/showthread.php?t=182999

I thought it had a full exhaust, which is a relatively easy fix with EFILive. I'll take a closer look in a few hours. Also there was another extremely problematic LMM dually at my dealer for a long time with the same huge rims, and GM said the rims can throw off the calculations in the PCM and actually cause limp mode. (???) If that's the case, that would also be an easy fix.

Does this all sound crazy? Thanks in advance for your input, I feel like these problems with the beloved almighty LMM are likely to continue as more people buy them and add accessories. I want to be on top of things so I can rescue them all with my EFILive :)

[Cobra#3747]

any codes for the limp?

Sounds like a low rail pressure issue, bad fuel or something floating around in the tank. Possible pickup tube problem?

[Boost]

I haven't worked on it but I know it repeatedly sets several codes, including 2459 and 0402 (both could be caused by intake / exhaust mods). From my experience 0402 regularly sets on LBZs with exhaust. I know for a fact this truck had a straightpipe right after the "atomic bomb". It may not have cooled properly because of that. Now the exhaust is back 100% stock, if there are any more problems I would suspect the large aftermarket wheels/tires.

[Donovan]

That really sucks for that guy. Especially if GM tells him that they wont buy back since things were modified (if that is in fact what happened). I know the feeling though when you can't put exhaust and intake in without coding every 30 seconds. I am so happy for EFI live for that reason.......Maybe you should try to help!

[Boost]

I would like to but my managers at work want me to stay out of it for now, since he is threatening legal action against GM. It's understandable from the customer's point of view, just a shame that the dealership is limited in what they can do for him, and he's getting upset and shopping for other brands. I would just like to know for future reference if I COULD have helped him, because this is bound to happen again (I know the owner of a local muffler shop is going to straightpipe his LMM soon, and is already asking about me).
This customer also has to be more consistent with his information. When I go to the doctor, I tell him that I'm an alcoholic because he's trying to help me... :beer:
:) :) :)

[Cobra#3747]

How does the tires size effect DPF regeneration happening to frequently?

Mileage being so far off on tire size?

[Boost]

GM (after many days of thinking about it) explained to us that the dramatic increase in tire diameter will throw off something in the factory program (they may have mentioned requested torque?). I know I'm being very vague, maybe someone that is aware of this issue can help me explain better. I can think of a number of ways it can possibly cause trouble. One is less miles traveled, as mentioned, another is a lower vehicle speed read (regens happen at certain speeds?), also could the torque being produced be misread by the sensors in the tranny? All I know is: adjusting for tire size and turning off DPF related codes with EFILive HAS TO fix most of these problems. Also if I'm not mistaken most of the problems happen while towing. I need an LMM for a testbed - accepting donations LOL! As soon as I find out some more solid info I will update. Thanks.

[Boost]

So apparently the engine's powerband and the tranny's gearing are a perfect match for each other. When you increase the tire size significantly, you reduce the gearing and make the engine fall out of it's powerband? Then the truck has to work extra hard uphill and with a load and sets codes. If anybody's familiar with this please explain it better. All I know is that it's a real problem that has happened multiple times already, and GM is aware of it. May be part of the reason the do not approve of gear and wheel changes on diesel at all, and the Tech2 cannot even adjust for bigger wheels.

[Donovan]

Is that only an LMM thing? I have some buddies rolling around on 35s on LMMs with no problems to speak of. How large are the tires that this guy was running?

[Boost]

22x12's Western Stars W/Toyo shoes

[Dale]

I am assuming hes also running a fairly small sidewall (didnt look at thread).

But 22's with a small sidewall cant be that much larger then the stock tires on a full size diesel.

Ive seen several HD2500's here on anything from 20 to 26's. But as for problems, I dont know.

[Donovan]

22x12's Western Stars W/Toyo shoes

What size of tire?

[Boost]

I'll take a look tomorrow morning.

[comet07]

What happened with the rest of this situation? did you figure out the problem?

[Boost]

I did not get involved, the truck was here for a long time but it's gone now. I'm not sure what they did, I just saw that they detailed it and it drove away. Wish we could have learned more from this case.

[540sscamaro]

I have 35s, 5inch exh, cold air intake, 6 inch lift and tow a 33 foot enclosed trailer, i have no problems with any of the codes you talking about, but one thing i do have is problems with getting any more injection timing out of it to make big power, I understand there is that issue with the lmm

[Boost]

What seems to be the problem with getting more timing?

[540sscamaro]

Just downloaded the new file that Ross unlocked, Timing isnt a issue any more, We will have it on my Dyno in the morning.

[DuramaxPowered]

Just downloaded the new file that Ross unlocked, Timing isnt a issue any more, We will have it on my Dyno in the morning.
What is the problem with timing? My stock tune doesn't seem to follow any certain timing table and I can't figure out why. The numbers will be close at certain times during a log, and be WAY off other times :bash:......

[camcojb]

What is the problem with timing? My stock tune doesn't seem to follow any certain timing table and I can't figure out why. The numbers will be close at certain times during a log, and be WAY off other times :bash:......


no real problem, just realize there are several different base timing tables depending on altitude along with several different modifier tables depending on ect, air temp, egr on/off, pilot(s) on/off, etc.

Jody