ok, he was getting 16-17 avg when he first got the truck. got a 4" magnaflow system. ran better, but mileage went down to 13-15. now he got egr blocker plate, finger stick, no cat, k&n air filter, and running amzoil if i remember right. less than 30k miles on the truck. changed the fuel filter less than 5k miles ago. he just went on a trip to the coast, and pulling his 18' blue wave boat. says he was getting 10 mpg on the hwy. what is the deal? what can he do to fix it??

My turbo went out at 40K...my truck also got worse mileage the closer it was to going out...dealer should warranty it...have them check it out.

wouldnt that effect the power/performance? cause i know he said it drove great. didnt even notice the boat was back there, which i can figure on that one.

My truck is in the shop right now getting the turbo replaced. Mileage has been dropping and I have been driving like the proverbial little old lady until the check engine light came on. I had codes 401 and 299. Tech said rear bearing in turbo bad, and EGR valve too. He said this was the cause of low mileage

bearsfolks, what yr is your truck? i know that his SES light aint coming on yet, and he aint got any codes yet. i might get him to get the turbo checked out.

It's a 2005 with 45,000 mi. As the mileage got worse I tried the Hypertech Max Energy E-Con, without improvement. After 6 months I then got a Banks monster exhaust and intake with slight improvement. Two weeks later I got a code. Mileage on the DIC went from 19 hwy to 17, and in town from 15 to 13.

First get rid of the K&N and clean the MAF sensor. Probably oiled up from the filter. I trashed mine months ago and truck hasn't skipped a beat since.

NOT saying that this is the problem but do it anyway.

How can you check and see what shape your turbo is in if you havent gotten a code yet. Because i think i am having a similar if not the same problem. I have put on a tx Cai, have a bully dog triple dog, blocker plate, no muffler, change fuel and air filter regularly, sinthetic oil and drive like a grandmother around and the best mileage i have ever gotten is 14 city and 16.2 highway going 70-75mph, and lately it has droped to 11.8 city and 14 highway. turbo going bad? any guesses? Thanks

pmdickso, thats pretty much the same thing. anybody got an answer to what he asked?

westx4, what filter did you replace it with? i know i have cleaned my MAF before, but how did you clean yours?

One other thing, either of you run any type additive / injector cleaner through your tanks? Stanadyne and Racor are "approved" by GM but there are many other good products out there.

I ask as (and it may be unrelated, but) a co-worker was talking to me about how his Cummins has gained 2.5 hand calculated miles per gallon after I gave him a bottle of Stanadyne to try out. His truck is an 05 and he'd never run any type of additive prior to the bottle I gave him. I gave him a bottle to try after a ride I took with him and I noticed his truck had quite the rough idle, I was figuring either fuel filter or possibly "gunk" buildup on the injectors.

He's also been driving like a "grandma" the past several months due to the raping we're all taking on Diesel prices. Our best guess, Diesel's don't like to be puttered around in, not enough heat to burn off the crap from the injectors. The additive seems to have helped him quite a bit, you may want to give that a whirl.

Worst case you burn $5 worth of additive and it does little to nothing to improve your mileage, best case you re-gain the mileage you've lost as you had build up.

Did the initial drop in mileage coincide with the introduction of low sulpher diesel? I lost almost 2 mpg when they switched. Got some of it back adding Stanadyne and two stroke oil every tank.

i use lucas about every 2 or 3 tanks. should i use it more often? or should i use a different kind?

Mine did the same exact thing without throwing codes. After running two complete tanks of B20 biodiesel and changing the fuel filter all is good again. My mileage is back up to 17-19 from 15-17.

he runs diesel kleen in most of his tanks. i know the fuel filter was changed just about 3-4k miles ago. dont know what else to say.

i think he is either doing something else, or has already done it, and aint tellin me. he is always putting it on me to find out whats wrong with his truck, and i told him to begin with that he needed to get an 04 to begin with so he wouldnt have to worry about all the emissions stuff to start out with. i dont know. i will leave it up to him to try to figure something out. i have tried to guide him in the right direction since day one, but he dont wanna listen. so i think he can figure it out.

yall think diesel kleen is better than lucas?

My opinion, take a look at the lubricity study which was done on this forum (it's in the maintenance and fluids section). You'd be hard pressed to go wrong with one of the top performers listed there. Not all of the products tested (2 stroke oil as an example) have cleaning agents as part of the product, so be sure to note that in the product description. Some products actually make your fuel worse as far as lubricity is concerned, they may clean good but as an example would you rather clean your hands with sandpaper or soap? Both will scour grunge off your hands, one removes a layer of skin to do so the other is a bit gentler in how it goes about it's job ;)

Some diesel additives (while it's an extreme example) behave similarly in what they do to the fuel system in your truck.

pick your own poison

ok thanks