2007 LBZ 6 mpg in town

[Raines Iron Works]

Hello I'm new to the Duramax family. I have a 2007 lbz with 107k miles
Bone stock with factory size tires. I just checked my mileage for the first time, the dash said 13.8 but actually it was 6.3 driving like a grandpa for the most part.
What's wrong with my truck?
Thanks in advance

 

[TheBac]

Welcome to the site, but I have to ask why you arent taking the truck to a shop to have it checked out?
Theres no way to know whats going on with the truck with so little info and no history. Its best to be diagnosed in person.

 

[ChrisPerry]

I'd say check it again. I'll bet the tank wasn't full when you started the mileage.

 

[Raines Iron Works]

I would take it to the shop but I work close to 70 hours a week right now so I have not had the time. I just bought the truck a few weeks ago. From what I can tell it was a grandpa truck before with a 5th wheel hitch.
I just ordered the EGR blocker and finger stick hoping that will help
All fluid changes and filters are current. I'm not sure what can be going on.

 

[Raines Iron Works]

Also I topped the tank drove 118 miles and then re topped the tank at 18 gallons my math got about 6.5 mpg

 

[ChrisPerry]

Is it possible someone siphoned off some fuel?

 

[Raines Iron Works]

I don't think so ChrisPerry. It has been a constant 1/4 tank a day on my 26 mile commute. I have a 59 F100 with a pi$$ed off 300" straight six and it does better than my modern diesel. The only thing I can think is a EGR malfunction or plugged cat but it has not thrown a CEL and it has plenty of power.

 

[THEFERMANATOR]

Look for fuel leaks. I'm north of 400HP to the wheels with mine, and couldn't get MPG that bad if I tried. My WORST tank has been 10.2, and that was towing a box trailer that weighed close to 10K and stood almost 12 feet tall, running 70+ GETTIN ON IT! Otherwise you're going to have to give us something to go on here. And I HIGHLY doubt even a stuck open EGR valve would drop the MPG's that much without MASSIVE amounts of black smoke and running like crap.

 

[ChrisPerry]

I'm with Ferm here. I got 12.5-13 towing 10k at 75 with a hung open egr that cause a steady haze from the exhaust. I'd think at 6 mpg you would be rolling smoke everywhere you went.

 

[Raines Iron Works]

Just a quick update. I finally got a few minutes today between job 1 and job 2 to roll under my new to me truck. No fuel leaks anywhere, in fact the only leak is the rear output seal on the T case. I'm still stumped
The exhaust is clean until I mash the pedal and no haze at idle. I guess it's time for the shop . Is anyone on here from around Folsom California
I need a good mechanic recommendation
Thanks in advance

 

[Tothemax]

you differently have something going on. I have two 06 lbz trucks. my dually is heavy over 8500#s with 33'' tires and tuned and pulls down 13mpg and my crew cab short bed with bigger turbo and injectors drives around on a 700hp tune and still gets 14mpg

 

[N2BRK]

Is your odometer off?

 

[jlawles2]

Does the truck do a lot of idling during the day?

 

[greendury]

Last three tanks through my 07 lbz have all fell between 16 and 17 MPG. Truck is bone stock.

 

[Scarface39]

Does the truck seem down on power

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[torqued2dmax]

If the grandpa was making his own bio fuel out of his old tractor oil,cat is almost blocked ,also the egr .Just a thought anyway.

 

[a8nistor]

Folsom, ?!! GO TO Orangevale Diesel. Local Diesel pros for sure. I'm from Auburn, CA. Just half hour from you

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[2004LB7]

Just a quick update. I finally got a few minutes today between job 1 and job 2 to roll under my new to me truck. No fuel leaks anywhere, in fact the only leak is the rear output seal on the T case. I'm still stumped
The exhaust is clean until I mash the pedal and no haze at idle. I guess it's time for the shop . Is anyone on here from around Folsom California
I need a good mechanic recommendation
Thanks in advance

Im in folsom, pm me. I have a v2 and can get some logs to post up for every to see.

I wouldnt take it to orangevale diesel, rude poeple in my oppion. I would go to Folsom Diesel Works on Sibley

 

[Hambone]

Just some personal experience
I have an Ac compressor going bad on mine right now and I've noticed about a 1-2mpg drop because of it...
not saying it's your problem but you definitely should look at all your pulleys and make sure non are binding up

 

[a8nistor]

Im in folsom, pm me. I have a v2 and can get some logs to post up for every to see.

I wouldnt take it to orangevale diesel, rude poeple in my oppion. I would go to Folsom Diesel Works on Sibley

Well, always a different opinion.

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