Engine/Transmission (1994 - 1998) Why is my mpg so bad?

[CBrabec]

I bought my '95 with 225K on it last October. Anyway, I had my transmission built, custom grind fuel plate all the way forward, new exhaust and a set of new injectors put into the truck (5x. 012" I believe). The guy who did all this work told me that he adjusted my timing to 16. 5* since he put in the new injectors. Anyway I pull a lawn trailer daily which weighs maybe 4K loaded. Two weeks ago was my first time pulling since all the work and my mpg was 10. 9 mpg and this last week it dropped down to 8. 6mpg (215 miles on 24. 8 gal). What gives? The truck defenitly has more power but my mpg is killing me! I am going to double check to see if the timing was truely done. If it wasn't done would that be a cause to the horrible milage? What else can I do?

 

[The patriot]

Driving style has a lot to do with MPG's.

Are you trying to get good MPG's, or are you checking out all the new work?

 

[The patriot]

PS Ever do the KDP?

 

[CBrabec]

I don't know if the KDP has been done since I bought the truck used, but I'm going to check it & fix it if needed. As far as to driving style, I don't drive it like I stole it. With the fuel prices I'm very conservative when driving. I talked to John who worked on my truck and he is going to send me a different fuel plate that doesn't have such an agressive grind to it and I'll give that a shot. If that doesn't help he suggested that I have the pump bench tested to see if the compression is still good and possibly have it rebuilt if needed. The truck does have 227K on it and I believe that the previous owner took good care of the truck since the body is almost perfect, interior almost flawless and the motor seems strong. John told me I should be seeing at least 16-18mpg towing my 4K lb trailer with what I've done to the truck. I really would like to be up in that range.

 

[KRStone]

What size tires? Are they aired properly? Large tires can impact mileage. Also, large tires can impact odometer accuracy. Alignment good? It's better to drive down the road rather than plow it



Towing in town or city? Do you leave the truck running when you're at a job?



I kind of smirked when I read "I'm very conservative with driving. " Really?



IMO, very conservative means:

losts of coasting

NO black smoke out of the tailpipe

Never above 5 psi on the boost gauge



Not many people are Very Conservative with their truck when it's brand new to them and "go fast" goodies were just installed.



Give yourself an honest tankfull of relatively conservative driving and see how it goes.



What is your trans temp? I wonder if your torque converter is locking up properly?



That big of a reduction in mileage is worrisome.



Check your oil level RIGHT NOW to see if you have serious fuel dilution (new injectors installed, right?)



Do you loan your truck to your workers much, hehehehe, they'll drive it like they stole it!



KRS

 

[JMcCoy]

If you drive "conservative", it doesn't matter what fuel plate you have in it. You could take the plate out and still get the same fuel milage as a stock plate, if you drive "conservative". Like stated above, if you have larger tires, it will throw off you calculated milage. My tires are 16% off so I have to multiply my milage x 1. 16 then divide by gallons used. Your milage numbers just sound so bad. Please keep us posted.

 

[wcjp]

Have you checked the fuel lines for dryrot? Don't forget the fuel preheater to lift pump soft line. Have you checked the brakes after driving with an infrared heat gun? You mentioned plate was all the way forward. Try more towards center. Air filter clean?

 

[CBrabec]

KRStone, to answer your questions: My summer tires that I am running are 325x60x18 which are a 33" tall by 13" wide tires so not tall tire compared to my winter tires which are an 285x70x16 which is a 33" tall by 12" wide. Not sure the width will make much difference. I do 95% towing in town/city and my tires are 5psi below max. I had John Issacs at Floor it Diesel build my transmission so yes my converter locks up properly and my transmission temp is anywhere between 140*-170* while towing. Yes my injectors are brand new and no there is no fuel in my oil. I don't loan my truck to anyone to drive, I am a sole owner/operator of my lawn business.



I guess when I say I drive conservative that is different than your thoughts, no I don't stay under 5psi ( I tow which is impossible to do) I don't coast and yes I love to blow black smoke but ocassionaly. I build my old '03 (before I sold it) to 900hp so this isn't my first diesel. Hell I got 15mpg when I towed with that truck, I was heart broken to sell that truck but had to for family reasons. A buddy of mine has a 94 and loves his 12V so that is why I decided to buy one. When I say I drive conservative I don't mash the pedal all the time and run it at WOT. Yes I have to get into the pedal when towing but other than that I'm pretty good. What kills me is that when I drive empty on the interstate or highway I can get 18-19mpg (of course there's no load), but when I tow (which isn't heavy) it drops horribly. Two friends of mine own 12V's, one with a 94 (2wd) and the other with a 96(4wd) and my buddy with the 96 when towing (same kind of trailer and amount of lawn equipment) is getting 17-18mpg in town and I'm currently around 9. I'm going to try the new fuel plate John sends me and see if that works and if not I'll get the pump looked at. I'm out of ideas as to why my milage sucks when towing.



WCJP, no I havn't checked the fuel line stuff and I will do that because I need to install a new fuel sending unit in my gas tank so I'll do that when I tackle that job. Brakes are new but I can double check that after a long day of towing. When John sends me the new plate I'm going to slide it back to the middle and see what happens, and yes the air filter is good.



Thanks guys for your advise, I really hope I get this figured out soon!

 

[KRStone]

Have you checked the fuel lines for dryrot? Don't forget the fuel preheater to lift pump soft line.

He said it starts just fine.

 

[JMcCoy]

The plate will not correct your problem. Unless you cannot control you right foot, that is. With 33 inch tires, you are approximately 11% off from your gauge. That means you are actually getting 11% better mileage than you think. Just because you had the transmission built doesn't mean the torque converter is locking up. How do you know? I would also add checking your injector pop off pressure to your list of things to check. Good luck

 

[Bob4x4]

A wide tire will use more fuel it will also be heavier than a skinny tire

Your friend is not being honest about getting 18 mpg towing in town. Driving a hot rod diesel is like driving a gasser. If you use the power your mileage will show it

 

[AEdelheit]

Should also check the brakes and alignment on the trailer , also what is your differential gearing? 3. 55 won't get as good in town towin as 4. 10's

 

[Axtell3]

I was thinking trailer brakes and bearing too. Trailers can be a PITA.

 

[Bob4x4]

A 400hp 12000lb rig is not going to get 18 city mpg and if you are blowing smoke... ... ... .

 

[CBrabec]

Your friend is not being honest about getting 18 mpg towing in town.

Actually his truck does, I let my truck sit this past week and he let me drive his so I could compare and I filled his truck at the beginning of the week and at the end of the week pulling my trialer and it got 17. 8 mpg (167 miles driven and used 9. 4 gal). When I bought my truck used and it was bone stock it was only getting about 11mpg towing, so I would have thought having a good strong transmission, new injectors, timing bumped to 16*, new gov springs, open exhaust & new cold air intake would have helped. I'm gonna try the new fuel plate and slide it back to the middle and if that doesn't help, have the pump bench tested to see what the compression is like and have it rebuilt to a 185 pump if needed.



I know my hopes are high, but I should be able to get atleast 15mpg towing my 4K trailer with this truck. Heck my old '03 that was built to the max got 14-15mpg towing my trailer. I am giong to upgrade to 4. 10 gears this summer so maybe that will help a bit as well.

 

[JesseGray]

I do not know what is good or bad, but I am on a 6,000 Mile excursion and this is my MPG experience.



I am traveling from Tucson, AZ to Plainfield, CT and return. I am driving a 1997, 5. 9l Cummins, 250, 2x, 5spd std, #5 BD plate, stock pump and injectors, BHAF, 3. 51 Rear, HTT 62 x 12, and LT 285/75R16 tires, pulling a 13,200 5th wheel RV.



So far I have traveled 2978 miles, using 217 gals of fuel for an average of 13. 7 mpg.



Conservative---no, I drive like I stole this truck. I have been setting the cruise at 2100 rpm, and through TN, NC, VA, MD, NY, CT, the truck has run 65mph over hill and valley. It is generally pulling about 10 in boost till the hills and it will pull between 10 to 30 in of boost. Generally, it stays around 900 egt.



I would like better mpg, but 13. 7 is acceptable considering my driving style.



This is posted so you have a not so good comparison.

 

[GAmes]

Having your timing at 16* is not helping you. Unlike computer controlled engines, the timing of fuel injection is the same, regardless of RPM. 16* is good if you are staying in the 2200 to 2500 range, but city driving is probably less than 2000 rpm. I'll bet if you set the timing to 15* the mileage will improve because the turbo lag won't be as bad, which will result in the use of less throttle to get the rig moving from a stop. I can tell you that with several hundred thousand miles of towing trailers of all sizes and weights that I don't believe 18mpg city driving for a minute. You may have only put 9. 4 gallons into your buddy's tank, but with such a small distance traveled even a few 10ths of fuel (different nozzle shut offs, different pumps, different surface levelness, etc) will throw those computations way off.

 

[SFrancois]

change fuel lines, I replaced my module inside fuel tank. It was loose, possibly letting air into fuel tank. I was getting bad fuel reading on how much fuel was in the tank. I was getting 200 miles per tank according to fuel gauge.

 

[K5IP]

Since you do you have a way to monitor boost pressure, is it normal? I remember having a rather serious boost leak when I had a 95 and my first indication was a serious drop in mileage, along with more smoke.


Rog