Engine/Transmission (1994 - 1998) MPG's going down, is it the new fuel?

[GMichaels]

Have a 1997 3500 4x4 with 4:11 and 5sp. put in a 10 plate and a gov kit.



when I first purchased this truck I was getting 15. 5 mpg. I thought that was low so I changed the fuel filter, cleaned the prefilter, checked for fuel leaks, changed the pressure valve on the pump. no change so I just accepted that this is what the truck's mpg's are. i didn't check the timing due to the cost. but the truck runs so nice, boost is good and egts are normal.



now I am getting 12. 5 mpg's and figure something must be wrong. could the low sulpher fuel be adding to the problem? Is there any other way to tell if the timing has slipped? I figure at some point if the mpgs keep going down the problem should become obvious.







I had a 1993 5spd 2wd 3:50 that got 22 mpg.

 

[EKlem]

Have you changed your fuel filter recently. ULSD is supposed to clean out your fuel system similar to running biodiesel so some people are seeing a lot of plugged filters. Once the system is cleaned out though, you won't have any more problems.



There is a lot of debate about what is going on with the winter blends this year but most people lose a few mpg when they start running winter fuel. There have been posts about decreased mileage from the new fuel but a lot of people are reporting the same or better mileage. Personally, my mileage hasn't dropped this year so I am wondering whether they are using additives rather than blending with #1 around here. Because of winter fuel, I don't think that you will be able to get a definitive answer on this until late spring when you know that you are getting straight #2 again.

 

[JGrover]

Not sure where you live,But maybe cold weather is causing a little mpg drop.

All the gearoils,motor oils can be slow flowing when very cold.

Keeping the RPMs at 2000 or less while cruising should yield a 19mpg truck.

I lost 2mpg at one time trying to cure turbo lag with the starwheel. MPG dropped to17 MPG :{ About 3/4 tighter, and back to 19. 7 MPG

I have . 354 gears though. 2000rpm@70mph (19. 7 mpg )Before Gearvenders install

In double overdrive with the gearvenders 1600rpm@65mph and 1800rpm@80mph (MPG 19. 8)

If you really like your truck and plan on keeping it a very long time.

Might be worth dumping them 410 gears for some . 354s

The GV is a $3000. 00 unit :{ Im sure some new ring gears in the diff would be much cheaper then a GV. With a 9k boat in tow, I can still pull any hill in 5th.

And that was with the Banks Powerpack stuff. No good fishys in the ocean now (fishing sucks):{ No reason to hook to the boat now. :{ Got the Hybrid turbo and #10 plate to do a tow test on

Hmmm..... That was a lot of imfo on fuel mpg. First put #10 plate in, 20. 4 MPG defuel the starwheel a bit, Now19. 8 MPG with 75/80mph driving.

MPG loss with new fuel?

 

[JWaters]

I never heard that the low sulfer diesel is a better cleaning fuel than the 500 ppm diesel is. Where did you here that? I have a 96 dually with a 5 speed and it gets 21 mpg highway and 19 in the city. I have a #11 plate and a k&n and straight pipe with 3. 54 gears... if you are getting 12. 5 something is big time wrong!!! I dont think it id the fuel... better start checking for fuel leaks!!!

 

[JFaughn]

Your signiture is not set up as most are familure with , there is no gages in it , a lot say that fuel pressure gage is not necesary with the P7100 pump , I disagree , the damage may be more costly with the 24v , but there are failures with every fuel system , then everybody is trying to figure out whats wrong , how to pressure test , ect , if you have a gage you can see the change happen [ lowering pressure ] , the lift pump has to be in good condition for the overflow valve to create resistance to increase pressure , so if you replaced the OFV and the pump is tired you may not get the pressure .
Your 4:10s are going to make for lower millage , if your in cooler weather , thats going to give lower MPGs for several reasons , the lube mentioned earlyer , but diesel make power with hot engines - longer warm up ,
So check your fuel pressure , if your mods are going to be near the mild end , a little bigger injectors , these trucks are detuned for dodges weak parts , adding a little more fuel has been giving many better millage , if they can keep from playing with the added power .

 

[KingS]

I have noticed with the new fuel a 3mpg drop in milage since useing it so I would say its is the fuel my self.

 

[bdcraig]

My 95' 3500 with the 4:10's gets around 15 to 16 mpg at 55mph. If I run 65 to 70 mph it will get around 11 to 12 mpg. Has been like this since new, even with the mods. Neither of my trucks has dropped in fuel milege on the ULSD.

 

[CSchafer]

They have been messin with our fuel around hear pretty badly. Both my dad's and my trucks have been very inconsistant on milage and power for the last two months. I was getting 17. 5 on 3/4 highway driving and now am down between 13 and 15 on complete highway trips. get 11-13 in town now, with new fuel. If it's runnin good just wait till spring to check it out.

 

[Vaughn MacKenzie]

Check out this thread https://www.turbodieselregister.com/forums/showthread.php?p=1661155#post1661155

 

[CCiatteo]

I have been tracking my mpg ever since I bought (May of this year, 159K) my truck (3. 54 gears) on an excell spreadsheet for a couple of reasons. The first is the obvious one, but other reasons were to track where I bought the fuel from (excessive water, noticeably poor performance) and as a new diesel owner I figured if the mileage fell off, it might be the only way I would know if something was wrong with the truck. So far, I am averaging 17. 5 mpg since I have owned the truck, but recently I got the best mileage so far 19. 2 mpg with the truck. Living in central NJ I'm not sure if we are seeing "winter" blends yet, but I am seeing more and more pumps with the warning not to run in 2007 and later model year trucks. I think this the low sulfur (500ppm)?, fuel. I have not run the ULSD, or at least been aware of it. This is something I will add to my spreadsheet and look for a long term trend. My driving is mixed and I don't tow or haul anything consistently so I thought these numbers were pretty normal for my situation. Maybe this helps someone???

 

[burnin oil]

spend the money to check the timing. Also check tire preasure and run the valve lash. I noticed that I needed to make a few adjustments to my 12v to run well on this ULSD. It smokes a little more under low to no boost but cleaner under high boost conditions. I knocked out an average of 21. 5 MPG over thanks giving going 630 miles and 19. 1 MPG over christmas on an uphill run. Even on my short commute to work I am still getting atleast 16 MPG. Time to tinker with your AFC and star wheel. Dont forget to try and get fuel at a high volume store, preferably where truckers get their fuel. Good luck.