loss in fuel mileage

[valleyrat]

I have a 99 250 7.3 turbo 4x4 that the fuel mileage will drop by 4 miles regardless of towing or not. Comes and goes. When I first got the truck I could get 18-19 mpg but the best I get now is 14. There are no codes, New air filter, new fuel filter. Don't know if this is relevant but I've run diesel kleen every fill up since I've had it. Thanks in advance for any help ya'll can provide.

[valleyrat]

is there another site that can help me?

[harperc]

Check you hubs and brakes for dragging. Also have heard cold weather fuel can cause bad MPG. I also sent you a PM.

[probuilder]

I would check the fuel filter drain valve. Mine was leaking and dropping the fuel right out the tube and down to the bottom of the motor on the passenger side. Replaced the o rings and wala, back to 19 to 20 mpg Just a thought, and my 2 cents

[valleyrat]

Thanks guys for your replys, The loss in mileage has been happening for a year or so and the winter fuel mix makes no difference, as it also happens in the summer. When I was researching this site and another for a possible cause I came across the drain valve issue, fortunately that wasn't my problem but a friend was having that problem and I was able to tell him of the fix. I forgot to mention earlier that my driving habits are very good. I found out a long time ago I got best fuel mileage if I kept it in cruise control as much as possible while bumping out of overdrive on steep inclines while towing. Thanks, keep it coming.

[dray8165]

Check out this page. Several people have had dramatic results cleaning out the exhaust back pressure sensor tube:

Welcome to guzzle's Exhaust Backpressure Sensor Cleaning Maintenance Web Page

[icysmooth]

good info on link

[valleyrat]

I recently replaced the ebp sensor and made a new tube for it.

[valleyrat]

Still looking for help. I'm getting 20 lbs of boost, so I don't think there's a problem there. Wish I had a compression gauge when I recently replaced my glow plugs. Maybe a problem there? This is my first diesel so I'm on a learning curve. I've restored several vehicles, and am a millwright, well unemployed millwright. So I know my way around tools, but I'm having problems wrapping my mind around this loss.

[dray8165]

You said you made the tube for the EBPV - I don't want to be insulting, but are you 100% sure it is leak proof. The reason I ask - another owner recently had a similar problem, and when he went to reinstall it, he messed up the nipple where the tube goes on. He wrote back that cleaning the EBPV hadn't helped at all, and that he wasn't sure he needed to fix the nipple problem. Well, he replaced the nipple, and with the leak free connection, suddenly the EBPV cleaning had indeed completely resolved his problem.

I would also make sure the hoses going to the MAP sensor are intact - being a '99, you could have some dry-rot.

I wouldn't worry a lot about compression unless you are having bizarre amounts of blow-by. I'm sure you've done all the maintenance - clean oil, differential full of clean gear oil, no brakes dragging, tires inflated (as per President Obama's directives).

No fuel leaks anywhere? You said it is a 4x4 - any chance the hubs are not disengaging? Is the torque converter locking up at the appropriate time? What speed are you driving? What is the RPM at that speed?

I'll try to come up with more suggestions when you respond.