Bad fuel mileage?

K

K204DR

I'm the Driver
Joined
Jun 30, 2008
Messages
971
so, my truck used to get 19 mpg driving around. the last year or two, its gone down to 16 or so.
I've been thru the injectors, fuel supply, everything I can think of, doesn't get any better. only thing left is the injection pump.
the truck runs smooth, plenty of power. Is it possible the injection pump is worn, killing fuel mileage, even though it has plenty of power?
I am at a loss, my buddy blows more smoke with his truck, and he still gets 19-20 mpg all the time.
any ideas beyond the normal?
 
check for boost leaks, maybe change your rearend oil to synthetic, might have a dragging brake. theres endless things to look into.
 
ive checked for boost leaks, running synthetic in the rear, changed to disk rear, and no draggin brakes. just wondering if the pump is getting tired.
 
well the mileage is getting worse towing. was getting 13 towing my scout on a trailer two months ago, now I'm getting 11. WTH?
I don't understand it. my friends trucks are getting 15 towing.
really starting to pizz me off. I want my 19 back. how is my buddys truck getting better, when hes got the whole front axle rotating, and I have lockouts in the front.
 
timing was at 19 and I moved it to 18 to see if it would change. seems to be the same. I did take the copper washers out of my pump a couple years ago, that wouldn't do anything like that would it? I'm out of ideas.
 
how much fuel pressure do you have? does it need a new overflow valve. sometimes when my 94 filter is starting to plug pressure will drop 5psi or so and millage will fall off? also how long has it been since valves have been adjusted? cummins say every 24,000mi to adjust them i believe. p pumps like 20 psi idle and close 30psi or more when reved up
 
Here's a dumb question. Have you looked at the air filter lately?
 
605 cummins said:
how much fuel pressure do you have? does it need a new overflow valve. sometimes when my 94 filter is starting to plug pressure will drop 5psi or so and millage will fall off? also how long has it been since valves have been adjusted? cummins say every 24,000mi to adjust them i believe. p pumps like 20 psi idle and close 30psi or more when reved up
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its got 35psi fuel pressure. I have the tork valve in it. fuel filter has been swapped with no change.
 
Got Smoke? said:
I'm willing to bet its your intercooler boots at the intercooler. The ones that transition from 3" to 4" they are notorious for getting weak and leaking causing a 2-3mpg loss.

Unfortunately there is not a inexpensive option to replace them, they best price and place to get replacements is Peak boots from Pure Diesel Power.
Peak Diesel Dodge 2nd Gen Cummins Diesel Performance grade Lower Intercooler boot
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I have aftermarket boots on it everywhere. I've pressure tested and have no boost leaks on it.
 
GAmes said:
Here's a dumb question. Have you looked at the air filter lately?
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the air filter is clean, and its a BHF, so its getting plenty of air.
may change the timing to 20 this weekend and see what that does.
 
What time of year are you comparing your mileage specs from and is the diesel fuel coming from the same place?
Air density/latency and fuel API can have a profound affect on engine performance. It could be as simple as your fuel source has changed.
 
Up north here they start switching to winter blend about now and you will definately see mileage drop from that. Now I would assume you guys dont need that down there but then again maybe they run it anyways for the big trucks goin across country? Just something to check into
 
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