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Engine/Transmission (1998.5 - 2002) poor mileage (been talked about many times, but would like to open a new discussion)

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Engine/Transmission (1998.5 - 2002) Limp Mode

2nd Gen Non-Engine/Transmission Front axle

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I hate to ask something that has been asked countless times before, but I would like to discuss poor mileage one more time. I just recently became a 24 valve owner, swore I never would but I did it anyways. Like most people on this site I truly enjoy driving, learning and working on my dodge diesel. so, I have been studying for countless hours reading on here and learning about my new truck. Like alot of people on here who have posted that their truck has gotten poor mileage since it was new, despite replacing every component on the vehicle with no gain in mpg, I must be one of those people. I am going to put up a kind of list of things that I have found in my searches and maybe if more people can chime in we can kind of get these things in one thread for others like myself searching for the answer. Keep in mind this electronics stuff is new to me, so here goes.



1) first thing I learned was IAT sensor, some give the wrong readings from the factory, some get dirty and become less resistive, clean or replace, could give you 0 to 3 mpg even if you think you already get good mileage. I cleaned then replaced with new and no change.



2)mapp sensor, I guess maybe it could get carboned up or give the wrong value telling the computer there is more air than there really is and matching too much fuel, maybe someone that knows more can clarify this. Cleaned mine even though it was clean, no change.



3)some have reported 3mpg loss after having the LP moved to tank at dealership, not sure what this is about, anybody have the answer to this one?



4) loss of boost, seems like this would cause low power because the mapp would still read the boost and computer would lower fuel accordingly, again i'm new at this, is this how it works.



5) lots of posts of people adding lots of performance items to gain mpg, gain power but no mpg.



6) there is one old thread I ran across that talked about the software, this is over my head but is the reason some never get good mileage possibly because of the control module program. If someone could chime in here, I have a feeling this could be the problem.





My truck best tank ever 14. 3 mpg that is driven with a light foot, highway driving cruise set at 1750 rpm. normally gets around 12mpg.
 
Dirty injectors or a worn out VP44 will impact mileage quite a bit. I have several VP44 powered trucks, and mileage is not always consistent. Best thing I have found to improve mileage has been a box that adds timing (Edge EZ, Quad, etc. . ) and even then it only will improve mileage if you keep your driving habits the same, which can be hard to do. It can't hurt to clean the IAT and Map sensors, but I only saw a difference on one truck, and less than 1 MPG at that. The Edge EZ did net me over 1. 5 Mpg gain consistently however. I am not sure why, but mileage is not at all consistent from one truck to the next. Good luck in your quest.
 
Dont feel too bad... I was horrified when I bought my 98. 5 24v truck. My old 95 1 ton dually with the same 3. 54 gear ratio and auto trans as the 98, consistantly got 23-24 mpg hwy... even with the pump turned up and a modified cam plate slid forward. The only other mod was I had drop valve timed the engine and set the P7100 to full plunger stroke at 16 degrees and the wastegate disabled. It also had 387,000 miles on it and still got this fuel mileage. On the other hand, my "new" 98. 5, has two less tires on the ground, has the same 3. 54 gears and auto trans... and only gets about 19 on it's best game day... with a new VP44 and lift pump. My thoughts are... just because it's "newer" and "more high tech" DOES NOT MAKE IT BETTER... and in the towing dept. the old 12 valve would get 14-15 mpg pulling my fifth wheel camper... the 98 24v does manage to crack 10 mpg pulling the same trailer... once in awhile, mostly it's around 9. 5 mpg on level ground. I'm dang tempted to P pump this 98. 5 OR sell it and replace it with a pre Jan 98 built truck that has a 12v in it. I've already spentway more money in four years on the 24v, replacing parts including 2 VP44s, three lift pumps and various sensors, than I did in the entire 10+ years I had the 95 12 valve truck. The old truck was still running great on it's original pump and injectors when I sold it at near 400,000 miles..... it was just starting to rust out and was going to need a head gasket soon... seeping coolant.
 
I was getting 17. 5 pretty much all the time since I bought the truck. as time went on the mileage began to drop until it hit about 16. 5, cruise on, off, level ground, hills, it seemed to make no difference. I pulled a 30 foot fifth wheel from NY to WI this summer, I got 10. 5 first tank through PA. While on this trip I broke down, had a new lift pump installed, that did not do anything but make room in the wallet. In Wisconsin, I found a great injection shop, they bench tested my injectors and found 4 with poor atomization and low pop off.



They replaced them with the rv275's. I got 13. 8 first tank home, and 17. 5-18. 5 unloaded, depending on how much smoke I make.
 
I was getting 17. 5 pretty much all the time since I bought the truck. as time went on the mileage began to drop until it hit about 16. 5, cruise on, off, level ground, hills, it seemed to make no difference. I pulled a 30 foot fifth wheel from NY to WI this summer, I got 10. 5 first tank through PA. While on this trip I broke down, had a new lift pump installed, that did not do anything but make room in the wallet. In Wisconsin, I found a great injection shop, they bench tested my injectors and found 4 with poor atomization and low pop off.



They replaced them with the rv275's. I got 13. 8 first tank home, and 17. 5-18. 5 unloaded, depending on how much smoke I make.



What shop did the work??
 
My fuel milage is bad no matter what. I have replaced the following items: VP-44, lift pump, APPS, IAT, MAP, turbo, injectors (RV-275s, Edge Stage 3s), new intercoller hoses.

Added: cool air intake, intake air horn, Edge Juice w/Attitude. I have changed tire sizes and types (285 x 75 x 16 Demonator all-terrians, Armstrong 325 x 75 x 16 mudders, currently runniing 285 x 75 x 17 Goodyear Silent Armour A/Ts) The only thing that appears to really make a difference in mileage is to drop the speed to around 55-65, I normally run around 75 at 1900 RPM on the highway. But my reality is no matter what 14 MPG is the norm.

I have heard that electrical issues could also be the problem, bad grounds, etc...



Good Luck, John
 
I own several of these trucks, and I have found that whatever you start out with mileage wise is pretty much what you are going to get throughout the life of the truck no matter what. My '02 auto started out at 14 in town and 16 on the highway, and has essentially remained the same regardless of mods; I did see about 1. 5 mpg gain with a timing box, but that has been about it. My '01 manual got 16/18 when I purchased it used, and in spite of having 220 hp injectors and twins among other things, I am still getting 15/18 with it. My '05 manual got 14/18 new, and now with around 100k gets 15/19 for the most part; break-in was probably a bit of a factor as well as the Smarty Jr, which helped a little under 1 mpg. I guess it's luck of the draw. It's too early to tell what kind of mileage I will be getting with the '96 12V as I haven't put enough miles on it yet.
 
I just read an article in this months Diesel Power about fuel additives. I am running Stanadyne, recommended by the injection shop, it seems to be good so far. only time will tell though.
 
My 98. 5 24V auto gets about 15. 5 empty and about 10. x pulling my 8,000# trailer.
I've blocked the wastegate, RV275s and ATS manifold.

didn't change a thing. More power if I floor it of course, but mpg? no change if driving sanely.
 
1998. 5 Auto Trans. with 290,000 miles--truck is weighted with tool box and gear. FASS and Banks 4" exhaust. The rest of the truck is stock. Truck gets between 15-16 mpg all of the time.
 
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