Your Lmm And Possible Mpg Fix.

[toypuller]

To start I am a technician at Parkland Chevrolet in Tacoma WA. We are the states largest volume dealership in the past few months.

I have heard lots of people complaining about their lmms and fuel mileage. Many more people have complained that after they got the ecm reflashed their mileage went way down.

Today I talked to our regional technical director Hank Pullmen, about the lmm and fuel mileage concerns that our customers are having.

As far as the regeneration goes I wanted to get some things straight. Things that I never new about the regeneration process.

The MAXIMUM amount of fuel that regeneration uses is 3 gallons per event. NOT 6 Gallons like some have stated.

The regeneration no matter what you tow or how you drive your truck on average comes on every 360-400 miles. The dpf soot is still calculated by the ecm, and how much fuel is used, how long you idle the engine all determines the actual regen events. Their is no warning that your truck is going into regeneration unless it hasn’t been able to meet the regeneration requirements.
(I.E) Your not driving fast enough 30mph to meet the criteria.
If you see a message in your DIC "CLEAN EXHAUST FILTER SEE OWNERS MANUAL NOW" and you don’t meet the requirements to make the truck go into regeneration. It then goes into limp mode. Limp mode is 2nd gear and 30mph

Our technical director right now is driving a 08 lmm with the ecm reflashed. The average fuel mile NOT towing anything is between 15.0-17.1 This is based on daily driving the min & max he has hand calculated. He has approximately 7,800 on the truck and mostly freeway driving.

Now to the point of this post. After talking with hank he has seen MANY lmms customers that are complaining about horrible mpg. The fix in 95% of the cases is the turbo outlet pipe/down pipe. Their is a bulletin on " Diesel smell on regenerations " What hank told me today is gm has found the turbo outlet pipe or down pipe is leaking right off the back of the turbo due to a flaw in down pipe production. This is causing an estimated 2 mpg loss in fuel mileage. Their is only 2 ways to see if its leaking, remove the turbo shield and look for black soot around the band clamp at the turbo down pipe. Or gm has an exhaust pressurizing tool that puts pressure into the exhaust system checking for leaks. I hope this helps anybody with an lmm motor. If you take your truck to the dealer just tell them that you smell diesel in the cab of the truck mostly during regeneration. That should trigger the tech to look for this bulletin. It DOESNT SAY anywhere in the bulleting that is tied to low fuel mileage. So DONT go in their complaing about that.

[bmich79]

thanks i give it a try.
2mpg is worth it for sure!!!

[AU Alum]

Thanks for the information, toypuller.

[08DMAXX]

Good to know thanks!

[n0useforaname]

Good info to know......but 15-17 highway isn't great....I get that in the City. Highway with a full truck and bed I get 18-19. Anyways.....are you saying that when a truck regens...it eats up 3 gallons of fuel??? Because that's not cool...... It's like taking 10 bucks and throwing it out the window.

[stymief16]

Thanks Toypuller, we can certainly use an insider! I'm not so sure about the regeneration occuring at a certain mileage range in all cases. I experienced several unexpected DTC 2549 codes that occurred only when I was towing a 15K pound fifth wheel across Canada. The code resolved to "Diesel Particulate Filter Regeneration Too Often". I believe GM has a service bulletins out that address this issue (and relates it commonly to towing), but I don't know if there's a fix. I simply cleared the code and pressed on with no issues.

[IdahoRob]

UMMM, not sure about 2 mpg. I've taken a couple LMM down pipes off for twin set-ups and seem the same as a LBZ which have had not problems.

I do not see how this would gain MPG. I could see the plugged DPF causing enough back pressure to start a leak at the turbo/downpipe band clamp, but that would not help MPG at all, may ever help it, if it was bad enough.

[toypuller]

About the fuel mileage, I am not sure why it would gain 2 mpg. I do know this is what the technical director told me. I should have asked him why, at the time i didnt think about asking why it would gain mpg. Either way its good information to have and hopefully someone will do and post on here that they did actaually see mpg increases.

[Killerbee]

Originally Posted by IdahoRob

UMMM, not sure about 2 mpg. I've taken a couple LMM down pipes off for twin set-ups and seem the same as a LBZ which have had not problems.

Just thinking out loud. Is the problem here that the dpf sees more regen because the leak creates a low temp condition downstream of the leak?

This would be the only rationalle I can with

[Buck]

Originally Posted by Killerbee

Just thinking out loud. Is the problem here that the dpf sees more regen because the leak creates a low temp condition downstream of the leak?

This would be the only rationalle I can with

That kinda makes sense but if it was a low temp condition then it would not go into regen because the parameters where not met which would increase MPG's until the filter was so clogged it was choking the truck and turning on the regen now mesg which would decrease mpgs? HMMMM?