Engine/Transmission (1998.5 - 2002) poor fuel mileage

[VolsFan]

Hi, been reading old posts about causes of bad fuel mileage. Have ran a few tanks through this 01 and it hasnt been that great, avg about 14. 5 I did better than that in the auto 99. I cleaned the MAP and IAT sensors, ran some diesel kleen through it. I know winter fuel makes some impact, but I thought this thing would be getting close to 20. It has 4. 10 gears, I dont run it over 65, been driving it very conservatively. The exhaust is still the stock 3", straight piped. I have a 5" w/ muffler coming in, dont know if that will make any impact. Previous owner said it has 100 hp injectors, not sure what brand, and it has a superchips flashpaq, I have it on the fuel economy mode.

Thanks

 

[Vaughn MacKenzie]

How many miles on the VP44? Checked for codes? According to Blue Chip website the advance piston wears on aging VP44s and doesn't advance as much resulting in gradual MPG drop.

 

[VolsFan]

Not sure how many miles on the VP, truck has 178k, has raptor fuel pump, fuel pressure warning light. Shows no codes. I want to ditch the warning light soon, need/want to get a laundry list of other things to it before that, not too worried w the raptor pump for low fuel pressure, hope its not the injection pump

 

[VolsFan]

Also, have not had any sypmtoms of a failing VP44 other than bad fuel mileage, truck starts up fine, has plenty of power, idles fine, no white smoke. APPS is fine. Have been blowing a lot of black smoke when shifting gears,(not intentionally) but think that was always the case with this truck. Not sure if its injector problem or what

 

[JR]

Was your 99 4. 10s as well or 3. 55s? Ive had both gear combos and the 3. 55s got me 1 to 2 better mpg , in my experiences anyhow. 100 horse sticks are on the upper end of the factory HX turbo, hence the black smoke and worse fuel mileage.

Also, Im not familiar with the tuner your running but with my Smarty I can achieve better mpg running a mild performance tune than the "economy tune" thats offered on it. You may try playing with yours a little bit to see if theres any difference. Ultimately, the right foot is going to be the single biggest contributing factor when it comes to good mpg's

 

[Gary - K7GLD]

"4x4" and "4:10 gears" sez it all - that plus individual driving habits and locales quite likely means that what you're getting, as what you'll get. The 4WD will eat 2-3 MPG, and the 4:10's probably about the same, and if heavy on the go-pedal, the bigger sticks will most certainly take their toll as well - and yeah a few will jump in here with better MPG's, but again, driving habits and typical driving locations can vary MPG a noticeable amount, in addition to the gears and 4wd... .

 

[jgillott]

You wouldn't have a stock set of injectors laying around that you could throw in few weeks would you? It would be interesting to pull those and see exactly what you have in there.

 

[VolsFan]

I dont have the stock injectors, I let them go along with the 99, it had 275s in it. I will play around w/ the box and see how that helps, then maybe have it checked out at the diesel shop I deal with and have them take a look at the injectors, maybe go back to something along an rv275 range. The 99 also had 4. 10s and I easily averaged 16 mpg no matter what I did. Also, my dads 03 is a 4 dr, 4wd, 3. 73 6 spd dually and always gets 19-20 mpg, on stock injectors w/ a bully dog tuner on low setting. I'd expect this mileage out of an auto but seems low for a 6 spd. I'm trying to control the smoke best I can w/out actually crawling from a stop, just wants to smoke like crazy on take off, I know that cant be helping mileage. Thanks for suggestions

 

[Bob4x4]

There is a big diff between brands when it comes to 100 HP injectors for the vp trucks. Some are dirty and wasteful while some run clean and still get good mileage. Do not assume you have good fuel pressure,any pump can get weak or fail

 

[charleyc]

You can improve your mileage just by having the right exhaust. The right exhaust will make sue all gases are being emitted out of the exhaust system. The engine does not have to work extra hard to eliminate the gases. So it will spend less fuel. You will notice the change when you use the exhaust system that is customized for your vehicle.

 

[JR]

You can improve your mileage just by having the right exhaust. The right exhaust will make sue all gases are being emitted out of the exhaust system. The engine does not have to work extra hard to eliminate the gases. So it will spend less fuel. You will notice the change when you use the exhaust system that is customized for your vehicle.

Im still waiting for the punchline

 

[AClayton]

Im still waiting for the punchline

:-laf:-laf:-laf



Anyway... . My opinion is that the 100hp sticks are overwhelming your stock turbo. I would find out from the previous owner what 100hp inj. he installed and go from there. Source a turbo that spools faster and moves more air and that will clean up your added 100hp sticks and improve mileage.



I had 100hp sticks on my stock turbo for about a year. I did all the tricks to move more air - even the trusty J-clip:-laf - and my truck always hit the 1200 mark pulling a load in OD. A quick downshift only meant the same exact thing, only 15mph slower. Finally solved it with twins about 5yrs ago and have never looked back. Even added Mach 4's with very little change in mileage! My truck gets 18 unloaded at 65mph and with the twins, only spools to 6psi boost to maintain my spdOo.

 

[VolsFan]

Im gonna have cv diesel take a look at it as far as injectors go. I liked the rv 275s I had on the old truck just fine with the stock turbo. I really dont have any near future intentions of going the compound turbo route, would be nice though,spending enough in getting the front end dialed in, just about got it. EGTs are fine, but it is mounted in the exhaust elbow, have not pulled hard with it yet. Overhead computer avg mpg says 19, but hand calculated and its 14. 8, I know this thing can get better than that. Not sure about the exhaust thing, I havent checked my mpg on this tank yet, but it has noticeably gone up since putting the system on. The old 3" exhaust was rotted out where it bends over the axle.

 

[RonaldLarson]

Tell us what size tries you are running. Anything over stock size affects mileage calculations in the negative direction.

 

[VolsFan]

they are stock 235/85/16 bf goodrichs

 

[georgej]

Some of the problem with fuel mileage at this time of the year is just getting that 1000 lb hunk of iron up to temperature. A winter front would help as well as making sure you have a good cummins or dodge themostat. Also make sure to check the air pressure in the tires. Your mileage really doesn't sound too bad considering the weather...

 

[JR]

If your egt probe is in the elbow at the back of the turbo keep in mind your egt readings will be cooler than if it was in the manifold

 

[VolsFan]

Thanks for replies. Still have not gotten it to the diesel shop I deal with. I think the bulk of my problem if not all lies in the injectors, havent driven it a whole lot. The truck heats up to 190 fairly fast, a lot faster than my old truck for some reason. I pulled the radiator out and pressure washed and flushed it first weekend I got the truck. Also, aware of the difference in temps, it rarely goes above 600, usually hangs out around 4-50o range. I am going to end up getting a 3pc manifold with the tap in it in the not too distant future.

 

[JR]

The truck heats up to 190 fairly fast, a lot faster than my old truck for some reason.

The one thing that comes to mind is higher combustion temps. Even though your egt may not be reflecting it, I would bet those bigger injectors/factory turbo is creating alot of extra heat in your engine. Post turbo egt's can sometimes be kind of misleading when it comes to a true combustion temperature reading which is why most people install their pyro on the manifold. Just a suggestion but it would be a quick fix to change locations. Drill and tap the manifold and then run a pipe plug into the elbow. More for peace of mind if it were for me

 

[VolsFan]

Right, I agree with that, might be a project for this weekend.