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/sho...d.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...

[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