Engine/Transmission (1998.5 - 2002) poor fuel mileage

[ESwartzer]

In the last week I finally found out where my mileage dollars were going. I had cleaned, adjusted and tried everything I could read on the TDR with no success. Long story short I had a frozen left parking brake cable with shoes worn into the rivets and a worn out drum. The passenger side cable could still move enough when I released the lever but it was pretty tight, the drivers side was frozen in the park position. I replaced all the cables, put in new drums, shoes, hardware kit and even new wheel cylinders (the 1/3/16 1ton gm) to the tune of around $250. I can already tell that my mileage has jumped back up into the low twenties on the road. I had no squealing no pulling or other indication that there was a problem, just the drop in mileage. Before you spend big bucks on engine parts I would check there, sometimes its the simple things that elude us.

 

[VolsFan]

Wow, thats crazy, I will check there indeed! I have four wheel disc, but I suppose the same sort of thing could happen. The fluid in the master cylinder is reading just a hair below full, and I inspected the front brakes to make sure brake pads were wearing evenly, but I will check out the rears for sure.

 

[VolsFan]

Got bosch 40 hp injectors and had valves adjusted. Truck feels a lot more responsive, a lot more pep in the low end. Runs really clean, little to no smoke. I have not run it long enough to check my fuel mileage, been hauling firewood which will affect it slightly, but from juding by where my fuel gauge is sitting at the mileage Ive gone so far on this tank, I think its going to be a jump in mpgs.

 

[jeepit]

VF. Sounds good let us know if mpgs improve for ya.

 

[JR]

Did you go with rv275s? Ive got a set sitting in the cabinet in the garage waiting for me to get em in. Was going to do it last weekend but wound up digging into balljoints and axle u joints and front shocks instead... much funner project

 

[ESwartzer]

Do you have full gauges? Sounds like your boost pressure may be too low. I would check the intercooler hoses for leaks and re tighten the clamps just to be sure.

 

[ESwartzer]

Also check your intake horn and manifold gaskets for integrity, you could be losing a little pressure in a lot of places.

 

[VolsFan]

I guess they are rv 275s, the shop told me they install a ton of them. I was just told they were 40 horse boschs, they didnt really know about the rv thing. They cleaned and pop tested the old 100 hp injectors and checked out fine. I have full gauges, I havent gone through the intake plumbing, but my boost seems to be in line, ill check it out though

 

[VolsFan]

Trying to unload the supposed 100 hp injectors that came with the truck. Number on them says 0432193635, and they are bosch. After doing some research, looks like they are rv275's. Not sure why they were blowing so much smoke, I guess they were just fouled up. Anyways, they are clean now, and I got a new set of bosch 167x62x65mm

 

[JR]

that number you listed is the number for the rv 275s but 275s are only about 40 horse not 100 horse. my guess is they are reman injectors, the bosch rv bodies with 100 horse tips. that or the guy you bought the truck from gave you some bogus info. is there any other numbers on the body? sometimes with reman injectors the last few #s will be xxx out and new numbers stamped below them denoting the new tips that have been installed.

 

[VolsFan]

I dont see any numbers crossed out, only other numbers are a 939, 083, 4183, then 4184 on the top. Atleast I know what is exactly in the truck now anyhow

 

[grimesja]

Good luck on the fuel milage. My 2001 has been at 14-15 mpg from day 1 when it was bone stock thru all the mods now at 303,000 miles.

 

[VolsFan]

what confuses me is that the overhead mpg says avg is 19 mpg. Im practically stock, except for the 40 hp bosch injectors, not running any kind of programmer as of right now. Havent checked my mileage since the new injector install.

 

[ESwartzer]

Do you have the stock tire size on the truck, could be the size doesn't match up with the computer programming. You could go to a highway with mile markers and check to see if the odometer is reading the distance correctly. Maybe the previous owner did a gear swap without mentioning it, anything's possible.

 

[JR]

Hey Vols, what kind of mileage are you expecting to get? Have you put enough miles on the new injectors to hand calculate some numbers?

 

[VolsFan]

I ran it a little bit, but it was hauling firewood and running in four wheel drive, so not my everyday driving, had about 175 miles on the tank and filled up and I only got 11. 8. Not too surprised being how I was using the truck, I'll see as time goes on. It could be totally possible a previous owner did a gear swap, which would account for the big difference in actual fuel mileage vs. overhead computer. Tires are the stock size. On my 99 auto, 4. 10 4wd, I had 285/75/16's and at 70 mph I was running about 2000 rpm. With this truck, at 65 its 2100 rpm and anything over that and its screaming and fuel mileage plummets. Not the end of the world that I cant go over 65. Im hoping that getting a chip that controls timing along with the new injectors will help me out

 

[PC12Driver]

Just caught this thread. Your mileage is exactly what it should be. My '01 3500 4x4 would get around 14. 5-15 in the winter months and 17-ish in the summer months for every year of the 12 that I owned it. Really not much different depending on my mods, either (stock to 450hp and back to 300-ish). Old or new MAP or IAT. So don't spend too much time or money trying to look for extra mpg.

Any engine mods will throw off the overhead MPG meter. The computer calculates the fuel flow based on a stock tune - there is no actual measuring of the fuel flow. So if you put in injectors that flow more fuel than stock with less effort from the injector pump, then the computer only sees the less effort and thinks it is getting better mileage. Put on a box or a programmer and you'll have the same thing. I think mine averaged in the low 20s for most of its life.

 

[VolsFan]

well thats good to hear, thought I would get better mpgs, but oh well. I am running the bosch 40 hp injectors and thats it, no box, and I like it. If i get another box it will be an edge comp, but for now, I like this smooth power band, does everything I want it to, and zero smoke. I have only run about 50 miles on a full tank since unplugging the box, so not sure what impact that will make, had it set on performance. I really feel no difference. Trying to sell the box and injectors on cumminsforum.com. I kinda feel dumb not having the diesel shop first pull the injectors and clean/pop test them before getting new ones, thought I was replacing 100 hp injectors. Im definitely taking a beating, but another life lesson learned.

 

[Keith graybeal]

Have you replaced or cleaned your air filter? Have you ran any injector cleaner through it.....

 

[VolsFan]

Yeah, I run a cleaner about every other tank. checked my filters, fuel and air, all that stuff. Drove lastnight and this morning and put 150 miles on it and its just starting to break the white line at full, usually I would be down to 7/8 by the time I hit 130 miles, so Im looking forward to checking these numbers. And none of it has been highway miles, been driving conservatively, I usually do.