Very poor milage

C

chev'in88

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Jul 17, 2012
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I recently bought an 04 lb7 CCSB that came with a bully dog triple dog GT tuner in it, has 305's on it and aftermarket exhaust. I have changed the air filter and just changed the fuel filter today. But I don't think that is the problem. Runs good. No diesel in the oil and doesn't smoke any that I can tell. The programmer is on the extreme setting but I don't get on it much. Could my injectors be starting to go bad and cause my fuel milage to be THAT bad? Filled up today and Was just under 13 mpg hand calculated. I have efi live to check the balance rates of the injectors but have to get my laptop fixed first.
 
Check for boost leaks and make sure you don't have brakes dragging. That's 4-5 mpg low for a lb7.

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The tuner shows it's hitting 24lbs of boost at WOT. If I do a boost leak test do I also need to cap off the turbo inlet when I pressurize the inter cooler piping? I tried this the other day and heard air coming from the inducer wheel side of the turbo like it was blowing through the waist gate maybe.
 
Should make over 30 lbs if you clamp the wastegate. You shouldn't have to, where are you putting air in? Should be in the hot side intercooler tube at the turbo.
 
Yes that's where I pressurized it at. Put 20lbs in it and could hear air leaking out of the inducer side of the turbo almost positive that's where it was coming from.
 
It shouldn't be. You sure it isn't a Y-bridge oring or something?

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I heard it coming out of the intake box back towards the filter from the turbo. Took me a while to figure that out I thought the hot pipe had a hole in it.
 
Weird, sounds like a intake valve problem then.

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But killing milage that much? I also just tried to clean my MAF sensor with some electric contact cleaner after I hooked up my scan tool to it and it was reading .31 lbs/m with the engine off. (Would think this should be zero) and after reinstalling it was erratically jumping from about .29-.32 lbs/m with the engine off. Checking injector balance rates tomorrow with a buddy's laptop.
 
As to being an intake valve problem wouldn't it be niticable somewhere else if persay a valve had a scor or something on it or the head
 
chev'in88 said:
As to being an intake valve problem wouldn't it be niticable somewhere else if persay a valve had a scor or something on it or the head
Click to expand...

I wasn't thinking, it would pop out the intake if the intake valves weren't sealing. But here's the deal. There is no valve overlap on these engines so it should NOT be coming out the intake. Pull your intake off at the turbo and find out for sure. I run 305 mud tires and get over 17 mpg around town.
 
Air it defiantly coming out through the turbo inlet when I pressurize the hot pipe side of the intercooler. I just tested it again. How is this possible?
 
chev'in88 said:
Air it defiantly coming out through the turbo inlet when I pressurize the hot pipe side of the intercooler. I just tested it again. How is this possible?
Click to expand...

That just doesn't make sense to me but I may be not thinking about something. Go to Duramaxdiesels.com and ask. I'm on that site a lot and it has much better duramax tech.
 
I'm starting to think its some sort of a head gasket issue but thanks for the help. Appreciate it! Ill try over there.
 
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