Low Fuel MPG on a C15 Cat Engine

Sounds like your fuel pump to me.

The fuel pump is the single most important, and sensitive component in the entire truck. It doesn't take much to foul it up, even a tiny piece of dirt that made it past the filter can kill your pump, causing your engine to miss, run erratic, and consume extra fuel. Have someone qualified take a look at your pump, and run it through the tests.

Good luck!

From your description it sounds like a part of your problem is transmission of power. Has your clutch been checked?

I really doubt you have a fuel pump issue but it could also contribute. If I were a betting man I'd want to see the codes on your injectors, all of them! Make sure the tech that checks them knows the Cat C15. They sound like they're wrong. Recode them to what Cat recommends. Make sure you get the trim code checked as well. Record all these values first, then make any needed adjustments.

After you do that and the truck runs better come back to the forum and tell us you entered code 6331. I really want to know! So come back.

Often the efficiency can be increased by a good quality locking fuel cap. Since the prices have gone up, so have thefts, and smart thieves take 5 gallons from time to time so it does not show as a huge loss at one time.

Just wanted to let you know I drive team with my wife and we stop only long enough to fuel truck and shower i take added caution to asure no one can get fuel un less they take my return line off when truck is running by the pumps and it can be over seen

I agree there is a lot of theft out on the roads .....I have been lucky so far

thank you for your input

With the electronic engines do nothing with out using the factory scan tool first then you may have some idea of what is wrong and what is indicating ok. O2 sensors will cause over rich conditions as well as other issues. They can be checked with a hand meter and a heat source. \you need to know which type of sensor and this is available on line. Follow instructions there are videos on you tube on this subject. My experience on electronic is Volvo but they are all a can of worms when not operating according to instructions. Test fuel pressure while operating this is very important since low pressure signals ECU to compensate injector timing on some systems. \let us know what you find.. Cheers

OK this sounds like a problem I had once with my cat engine, I had two major problems. the first one was, the inter-cooler had a leak and I was loosing boost PSI from the turbo. When I got that fixed I found that I was making oil, actually I had diesel draining back into the oil pan, this was due to a failed ring on my #4 cylinder. I had the engine completely rebuilt. afterwards I had great mileage over 10 loaded and @ 14 empty.

Ok just wanted everone to know I have found out some new things today Had the truck in for my service and shop owner and I had called CAT main office we had abot a hour or two call that revealed that when I had my last fuel pump put in it was a upgraded one BUT the 6nz series cat fuel pump has a new spring kit that maintains steady fuel flow and preasure at the injectors this we have parts on way and i also found out the atmos sensor eaven that there is no coad and is reading correctly will do some funky things

when i get these things in and tested i will get Back to all of you here thank you all for your input