Something isn't right

[J_Da_Fox]

I know you dont wanna see another fuel mileage thread, but bear with me for a moment before you ignore this. My 05 3500 was getting around 23 mpg. Then I removed the silencer ring, the cat and muffler, and the baffles from the air tube, cheanged the fuel filter, and added a drop in wix air filter. My mileage dropped to 19. I could put the nasty air filter back in and get my mileage back. Its progressively gotten worse. Now I'm getting 12 mpg. It doesnt matter if its empty or pulling the gooseneck. Any ideas?? And please no, "I've always gotten 12!!" I wasn't getting twelve, I was getting 23. Thanks

 

[J_Da_Fox]

23 to 12?? Anyone? Anyone at all?? So I changed the air filter last night with no difference. Fuel filter is clean. Turbo suckin the air like nobodys business and making all the ford boys jealous cause I whistle louder. Is there anyway I can delete this post cause I really feel like its not worth the time. Wait, I've got the answer. Only in Missouri!! Right?? Thats what we're always saying. Maybe I should move... Come on guys, humor me!!

 

[mberry]

Replace your Wix filter with a new Fleetguard and see what happens. From your description it would appear that you have a severe restriction on the intake side. Also check your intercooler boots to rule out a boost leak.



I put Amsoil 15-40 and one of their air filters (EAa189?) and got back the 2. 5-3mpg I lost with the stock filter and dino oil.

 

[jelag]

Fuel metering is controlled by the ECM, nothing you do with the filters, both fuel and air should make a difference with mileage... .

I own 3 3500's, 04. 04. 5, and 05, none of them has ever gotten more than 17 empty traveling on the highway and this usually drops to 10 to 12 when pulling 20K lbs of trailer... . My BIL who babies his truck..... might get into the 19's or so... I find 23 a very hard number to believe... . and the lower 12 to be right on when the trucks working... .

We use off the shelf air filters and fuel filters... . we do not change them often... . and put lots of miles on them... . from an engine stand point all my stuff is stock... .

 

[WUnderwood]

are you using the overhead computer or are these hand calculated results?

 

[J_Da_Fox]

Everything is hand calculated, and I change my air filter every 2000 miles. I don't believe the restriction is on the air side. I believe its not enough fueling.

 

[DrDiesel]

I would hesitate to guess, but the loss of back pressure on any exhaust system will cause problems. Proper exhaust scavaging is a big part of tuning.

The stock air intake tube has an air deflector inside to help reduce air turbulence to the turbo. :{

 

[J_Da_Fox]

I've installed a high flow muffler to reduce the harmonics of the straight pipe, and also the air deflector has been removed. Maybe you are right with looking at the the lack of back pressure and air turbulence.

 

[J_Da_Fox]

I'm just going to wait til it warms up and see if it makes a difference. Come on spring!! Yeah

 

[JHardwick]

I would hesitate to guess, but the loss of back pressure on any exhaust system will cause problems. Proper exhaust scavaging is a big part of tuning.

Scavenging does not apply to a turbo diesel engine.



My money goes on boost leak, I recently went through the same deal.

 

[J_Da_Fox]

holds 30 psi til the computer regulated wastegate opens, then my boost drops and holds at 25

 

[Prairie Dog]

This is a stretch but if you run one of those covers over the front that blocks the radiator, you defeat the operation of the intercooler and will have both a slight drop in power and fuel mileage.

 

[MCummings]

You cannot modify the backpressure of a turbo diesel, unless you change the turbo.

(edit: what I mean is, no matter what exhaust you run, stack out the hood, 6" out the back, or 4" with muffler, the backpressure change is insignificant. The turbo creates all the backpressure the motor needs, only when you change the turbo, is the backpressure changed. )



I would say a boost leak. Maybe a slightly parted intercooler (check to see if the end tanks are plastic).



Also be sure to check fuel pressure. If your Lift Pump is not pumping enough fuel, your mpg will drop significantly.



My two cents,

Merrick



EDIT: Also, you may have a dieing injector...

 

[cclark746]

very little are no back pressure is needed with these trucks i also would understand you concerns i have had an 03 04. 5 05 and 06 never seen no better than about 17mpg in fact my 06 auto is sucking the fuel like i havent ever seen before