Need help poor fuel milage

You have a turbo boost meter installed? I have one in the heap I'm driving now, and it really helps with saving fuel if you use it right. I try to keep it at around 15 psi or less if I can help it. Sure, everyone at the truck stop is going to talk smack about how they ran rings around you, but you'll be the guy at the end of the counter counting that extra $200 he didn't have to spend at the fuel lane.

 

dear fiend when you change the rear gears you need to hook up dddl and change the settings so ecm will calculate mpg correct. Same way you need to update the calibration settings when you change the wheels from 24 to 22.5 (or other way) ...

 

40-50 psi ? or your boost pressure gauge is not correct or your turbo is overspeeding. overspeeding can cause mpg go down... the turbo speed can reach max to 100.000 rpm and at that speed your boost pressure must be 35-37 psi. no more than that!

 

Is it a mechanical gauge?

If you are showing 30psi while cruising, then you have a problem. The more pressure while running, the more fuel you use.

Start with checking the air path from the turbo to the engine for restrictions and/or air leaks.

 

you must have 7-20 psi while cursing in flat road... no more than 20 psi.

 

Sounds like you are getting pressure from the EGR being closed when it should open up. A bad EGR being stuck closed can cause as bad fuel mileage as one being stuck open. Stuck open you lose power and stuck closed you are over boosting, which is what your engine is doing, which is causing the fuel to dump more because the engine is reading the boost being high.

Check your EGR operation.

Sit in the truck with key off. Start the truck. Wait for air pressure to build and listen for the turbo to start its spool up at idle. This indicated the EGR is in a partial closed state, but still allowing the gases to go through.

Now rev the engine 3 times. Not slow, but like you are sitting at a stop light revving your engine to race someone. Listen to the engine and you will hear the turbo unspool and the high whine should go away completely. Your EGR is now in full open state. Look at the exhaust and watch it. It will have a very small haze of color. The engine will go back to its regular idle state in a minute or two and you should see the smoke go to clear. If you are not getting the slight smoke during this time, your EGR valve isn't opening up fully and then is needs to be checked into further.

Technicians will do the same stap with a computer while recording for playback to see what the pressures are reading on the Delta P sensor and the boost sensor. There are specs for those to indicate the EGR is functioning properly or not before needing to change it out.

The EGR doesn't have a sensor on it. It is only commanded and the computer doesn't know what the EGR state is. It can only determine that by the pressures it is reading on the Delta P sensor. You can have the beginning stages of a full EGR failure and not have a code, yet. You see this a lot on the 2007 EPA engines and the dpf filter plugs up quicker than normal.

 

ddrs or dddl will show the problem quick...