07.5+ LMM Duramax PowertrainDiscussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission Ect
you have me curious... now I'm going to look that up.
This would not create any low mileage complaint unless there is an undue restriction in the DPF, which would also set a DTC.
On a diesel, tons of oxygen is not used in the combustion process, so the oxygen content is not appreciably modified by a tiny exhaust leak of that nature. And there are no oxygen sensors to affect either.
The EGT sensors on an LMM are located AFTER the catalyst has re-heated the exhaust by taking care of unburned HC's, so a tiny exhaust leak will have no appreciable affect on that either. And these sensor only govern the regeneration cycle, nothing else.
In short, a leak generated by a poor production tolerance in the downpipe that only seeps a bit of carbon will not change anything regarding mileage. However, a leak induced by excessive backpressure would - except that the Differential Pressure Sensor on the DPF would register the restriction and tell us about it.
Unless there is something else, I can't see how this potentially changes anything regarding economy.
__________________ 2005 Chevy Silverado, complete LBZ intake, baffles and compressor mouthpiece, MBRP 5" exhaust, 275/55R20's, Custom programmed by me.
I am a little bit concerned because I just got my gauges and exhaust. I have already started to install the gauges but I am definatly not going to do anything with the exhaust untill I take it in to get this checked out. I hope they don't bitch about the drill and tap into the manifold for the pyro sensor!
Sorry pjgmtech!! Talked to our technical director today on the phone. The reason is exactly what killerbee said. The reason is an exhaust leak actually pushes air out and then sucks it back it when the pistons go up and down... When the truck goes into regen it dumps raw fuel into the exhaust system. When it does this because of the exhaust leak it creates a smell ( i.e like the bulletin says). This means to make the pdf get to the actually temp that the truck requires it has to regen longer and has to give it more fuel to meet the temps required clean the dpf. It cannot be just a standard set amount due to elevation changes/air density. Thus causing the truck to use more fuel during regens and worse fuel economy. By up to 2mpg is what he is claiming.
He also said that it changes turbo velocity. Now I will be honest I have no clue exactly why that would change since its on the exhaust side. So please dont ask I am not calling him again. Maybe killerbee knows. He seems to be on his game.
Last edited by toypuller : 11-20-2008 at 09:09 PM.
I am a little bit concerned because I just got my gauges and exhaust. I have already started to install the gauges but I am definatly not going to do anything with the exhaust untill I take it in to get this checked out. I hope they don't bitch about the drill and tap into the manifold for the pyro sensor!
When mounting an egt probe you ONLY mount it in the exhaust manifold. Not in the exhaust system after the turbo. You need to measure the temps going into the turbo. Some people that are really anal install both pre and post turbo.
Install the gauges they wont care.
I don't really know much about these systems, but jp is doing quite a bit of research on them. I speculated on some rationalle for fuel economy decrease, but that very question has not been demonstrated to my knowledge. However:
It does seem to me that more fuel would be wasted in the dpf if it is exposed to any condition that would reduce its normal operating temperature (including cold weather). There are probably other problems that can command excess burn as well. But as I said, I feel like I am not very well qualified.
In my humble opinion, these systems are tragic. Somebody is breathing too much exhaust. My feeling is that the dpf, in its present un-evolved form, will be regarded as nuts as a bull in a china shop.
would it use less fuel if the dpf was wrapped in the header wrap tape to keep it hotter? would this produce other problems?
__________________ Tom's new truck: red 08 duramax lmm , LTZ, crewcab 3500 4x4, stock for now for towing racecar trailer #10000lb's , spray in liner, has black aftermarket ranchhand cowboy bumber with cowcatcher for that sinister look , matching back bumper, added a toolbox in bed , new lights on push bar chip to come later remember old age isn't for sissies !! never hollar whooaa!! http://i335.photobucket.com/albums/m...1/P9150004.jpg
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chip to come later remember old age isn't for sissies !! never hollar whooaa!! 
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