talk to jimmyhoud

https://forums.d2jsp.org/user.php?i=278087

Not the biggest duramax guy around but here goes.

Motor wise, these really haven't changed a ton. The LMM shares the same piston as the LBZ. These were known to be the weak link in the motor. However, the LMM stuck with the proven rock solid CP3 design and the newer LML moved on to the CP4 design which was pretty questionable and caused quite a few issues.

In stock form, the pistons in the LMM would be of no concern. People really only had issues at or above the 600hp mark and even then was greatly impacted by tuning and drive pressures. The CP4 in the LML is a wild card. While tuning for higher rail pressures would cause failure sooner than leaving stock, plenty of people in stock tuned trucks have had issues with them failing.

The LML trucks will have a higher GVWR and a newer frame design than the LMM trucks. Both still use an IFS so no huge differences.

All in all, get what you can get for the best price. the LMM vs the LML is pretty minimal in drive train differences. Both trucks will have DPF, DEF, and EGR so deletes would be highly encouraged on either (from me).

As for what to look out for. Make sure fuel delivery is good and there is no signs of blow by. Other than that, you're looking at trucks with 85k on them... pretty low for a diesel drivetrain. I will add. I would NEVER buy a used truck that already has a tuner and deletes done.

I just sold our last duramax truck. Was a 2wd 1 ton with 484k. Other than 2 cp4 replacements and a set of injectors, the motor / trans were never opened. Good trucks, shit fuel mileage though.

Looks like he's keeping it stock.

Very useful info, thank you! Anything I buy has to be bone stock because I know if it's already been tuned and deleted, chances are it was beaten down and romped on all the time. Deletes will definitely happen but I don't trust anything with a tune. If I purchase something between 70-100,000 miles, is there any maintenance I should do before driving it? For instance, is there any part that tends to fail around that mileage?

aside from just looking things over no. I wouldn't go out and spend money on replacement parts unless something was wrong. I'm not as familiar as some of the GM guys around here with typical failure points on these. Maybe they can shine some light on that for you. FMX is a pretty big GM guy.

If you find something worn out (ball joints, breaks, tires, belts etc) then sure, go ahead and replace them for the piece of mind but at 70-100k it's still just normal maintenance on these like any other vehicle.

Keep in mind, in order to do the deletes and the truck still function. The computer will need to be re-tuned to accept that those parts are no longer in service to run without going into a limp mode. Granted, you can tune for deletes without increasing fuel and air maps but odds are, some of the economy tunes will actually make the truck run better and more efficient than the stock maps anyways. Just stick to a reputable guy that tunes with EFI Live and you'd be set. I ran all of our duramax trucks through PPEI but i've heard pretty good things about the guys at duramaxtuners.com as well. I don't know who or where they get their tunes from though.

I'd be doing maybe two or three different maps. Nothing crazy like the 200HP tunes some guys run. Just a basic tow tune and maybe a 30-50HP tune. Also, since deletes are illegal but not strictly enforced I'll need to be careful how I drive.
Also..100k Miles isn't too much when buying a used diesel? As long as it hasn't been deleted and/or tuned already.

This post was edited by Fioravanti on Dec 8 2018 11:25am

Buying a truck with a gas or diesel motor at 100k is about the same as far as parts longevity goes. All your normal suspension, breaks, belts, waterpumps, etc still fail in about the same period of time. The only difference is the transmission is much heavier duty so they last longer than the gas trucks and the core motor will last much longer( anything behind the front accessory drive for the most part)

Also, as far as deletes being illegal. Yes, they are. It really depends on where you live though. I would say 95% of the US could give a fuck less as long as your not acting like a tool and smoking out intersections.

if his state has vehicle inspections to be road legal will deleting them make them fail? we dont have that in ky so i dont know what they check for in those inspections besides like emissions levels