well i just filled my truck up this morning and i checked my mileage with the odometer and i'm only gettin 12.5mpg...why could this be?? i change my oil every 5000, my AFE is always clean, changed my tranny filter and fluid about 10000 ago, and change my fuel filter every 10000..anyone have any idea's???

 

When looking at MPG issues, it's best to start by checking for boost leaks. The 6 boots on the IC plumbing, then check the up pipes for leaks.

Some have seen an increase in cleaning the EPB tube. Welcome to guzzle's Exhaust Backpressure Sensor Cleaning Maintenance Web Page

 

3 thing to look at..the exhaust back pressure sensor (EBPS)tube could be pluged..IC boots are loose so you making wasted boost..or the up pipes are leaking..
a how to for EBPS tube
Welcome to guzzle's Exhaust Backpressure Sensor Cleaning Maintenance Web Page
pull boots clean pipe and boots with simple clean

look behind turbo for any sighns of soot..if there is soot.9 times out of 0 its the donuts..

good luck

 

i checked the up pipes last week they seemed all good, no soot nothing and i fig if they were leaking i could probaly hear it too....anyway whats the easiest way to check for a boost leak??? is the only way a boost leak detector??

 

As Ron mentioned, you can take them off, clean them up, and re-install, or just take a ratchet and see if any of the clamps are loose.

 

lol guess im too slow..Chris beat me to it...I got to busy in the PM's..boost leak detector is the best way..you can build one like i did..but i have since found a nice one for 30 bucks..
Intake Leak Pressure Tester

 

i mean with my superchip on hi performance tune should i get more than 12??? i didnt think 35's would hurt the mileage that bad??

 

First - Is your speedometer calibrated for your 35's, and if so, have you double checked it's accuracy (such as comparing it to a GPS)?

Second - How are you filling up your tank? Are you filling it until the pump automatically clicks off, or are you filling it up until you see fuel, and not foam, in the filler neck?

The reason I ask these two questions is that there are a ton of variables that can affect your mileage calculations from one tank to the next. If the speedometer is off, and you are not correctly accounting for the inaccuracy, then your mileage will be incorrect. At the same time, if you are not consistently filling up the fuel tank to the exact same spot every time, then your fuel mileage will vary quite a bit from one tank to the next.

In regards to the fuel tank, there is a vent tube that extends partway down into the tank. This vent tube causes fuel to foam up as it fills up the tank. When the foam is at the point where it is overflowing into the filler tube, the pump will automatically click off as if the tank was full. In reality, you can put another 3-8 gallons worth of diesel in your tank before it is actually full and you start to see fuel instead of foam in the filler neck. This 3-8 gallon discrepancy can change your mileage quite a bit from one tank to the next.

The problem on a bone stock fuel tank is that to completely fill up that last bit with fuel, you'll spend another 20 minutes or so slowly dribbling in the last few gallons of diesel. Most people don't bother with it because it's so slow and agonizing to completely fill it up. This is why some folks drop the tank and do the "Harpoon" mod. This involves cutting off the vent tube inside the tank, allowing you to fill up the tank completely with fuel. I did this on my truck, and I only have to dribble in the last 1/2 gallon to see fuel in the filler neck.

Several other factors that affect mileage will be the winter blend fuel, driving habits, tire pressure, and engine health. Winter fuel will drop mileage lower than during the summer. Your driving habits play a big role, especially with 35" tires on 3.73 gears. You really have to baby the pedal to get decent mileage, especially in town. Same goes for keeping tire pressure correct on those bigger meats. Last, others in this thread have pointed to possible boost or exhaust leaks. These issues are quite common on the PSD, and will impact fuel mileage quite a bit.

So...... just some food for thought.

 

ok thank you for the good write up, i'm probaly going to make my own bost leak detector i was looking to clamp it on right where my air filter clamps on, what pressure would you recomend me taking the PSI up to for the boost system??? and for the pu-pipes leaking wouldnt i hear it?? and i'm guessing from underneath is the easiest place to see the soot?

 

For the boost leak detector, you only need about 10-15 psi to check for leaks.

As for an exhaust leak, you won't always hear it. Most common spot is right behind the turbo, where the up-pipes meet at the y-collector. Climb on top of the engine and look behind the turbo. If you see soot on the pipes, it's leaking. A mirror sometimes helps too.

 

Curtis,

You sure are a "fart smella'" .

If'n ya' don't git it, change around the first letters........

 

ok i think i'm going to try and build a leak detector and go from there...

 

i'm guessing the inlet oin my turbo is a 3inch?? soo i need a 3inch rubber coupler??? am i correct? or where can i clamp the coupler on??? where the intake tube splits or just right on the turbo?