5 inch mbrp turbo back lly

[daddysLBZ]

Originally Posted by SC DURAMAX 444

after i installed the exhaust on my lly duramax i lost about 4 mpg. i also kinda noticed a drop in power. the loss didnt happen until about 3 days after. i thought exhaust was supposed to up mpgs. im not sure if its the exhaust or what. about 8 months ago i had the same problem and it was my fuel getting air due to a bad seal on the fuel pump. does anyone have any idea why this is happening.

Sounds lke you don't have the hp for 5 inch pipes?The 4 inch will do fine for anything under 500 hp.IMO you are having some backpressure issues.The truck may be tellin ya you have too much pipe and not enough backpressure,therefore a loss of power.Try blockin rear of pipe carefully,then drive normally while reveiwing mpg status,I'll bet this is the culprit...

[daddysLBZ]

Originally Posted by Duramax_JP

I know this would be a hassle but put your stock exhaust back on and see if the new exhaust is really the problem. After so many people running 5" and not seeing this loss in power and mpgs i highly doubt the exhaust is the problem.

The main thing i wonder about is he said this happened months ago,so got me on that one...

[gr8shot]

Well first thing I'd do would be to put a new fuel filter on. Could have gotten a bad batch of fuel. It happens. Turbo'd engines don't need back pressure like a gasser does. the turbo provides all the backpressure the motor needs. After the turbo all backpressure does is raise EGT's, cuz the exhaust can't get out fast enough. Yes, 5" isn't necessary, but it definently doens't hurt anything.

The basics of how a turbo works, and how exhaust (or air) flows, is just air going from someplace with high pressure (cylinder & up-pipes) to someplace with low pressure (exhaust after turbo, and atmosphere) The bigger the pressure difference the less work the engine has to to do move the air, since the pressure difference, and natural tendency to reach equilibrium, will do some of the work also. Thats why the up-pipes are small, so that the air moves very fast, and will spool the turbo quickly. The turbo vanes are the restriction between the pressures, and the air must move the turbo vanes to get to the low pressure.

So, no, the exhaust shouldn't cause bad fuel mileage. I would look elsewhere. And you most likley would have noticed it at the same time you put the exhaust on, not a few days later.

[SC DURAMAX 444]

good news. today i took my duramax to the local gm dealer and told them my prolem with my mileage and power. it was the same thing as last time. the fuel pump had a bad seal and was gettin air yet again. it runs like brand new now but the tech said that the seal keeps goin bad becasue im demaning too much fuel out of the stock pump??? any truth to this??