ok i first off when i got this truck 2 months ago i was getting 12-14 MPG. i figured that was because of a bad filter. then it started ticking so i figured it was one of the injectors. and once i noticed the ticking i was getting 9-11 MPG.
ok so i had new stock injector tips put on. that fixed the ticking noise.
i had the pump turned up.
i had the timing advanced.
new overflow valve put on.
new fuel filter put on also.


ok now i am still getting 9-11 MPG. and that is taking it easy. is there something i am missing here that i am getting this bad of milage. its all bone stock except for the stuff above and a 4" down pipe to 5" straight pipe exhaust. everyone keeps telling me i should be getting 18-20 mpg stock and with the mods i should be getting a little better.

does anyone have any opionions????

also after i took it to this fuel place i noticed that the fuel heater assembly was burnt ontop were the wires go into it. and it was done recently also. i call the shop that did the work and he tells me that they go out all the time. that if any fuel gets on it it causes it to short out. well they just changed the fuel filter above it and other work. and well it wasn't like that before i took it there. and u can tell it was fresh as the wires are still copper colored.

do these really go out all the time????

thanks

 

The wiring harness to the pre-heater burning up is fairly common. You can buy a replacement at Cummins. DC will sell you the whole pre-heater assembly for big $. I hadn't heard about fuel on the wiring harness causing it to short out, but it's something to keep in mind when changing fuel filters.

 

anyone have any ideas?? i have a 35 gallon tank on it and i am getting anywhere from 300-385 miles per tank.


what is going on here?

later

 

You can remove the heater portion and just have the screen (prefilter). Remove the flter bowl, then the heater using an allen wrench in the center bolt. Reinstall the filter bowl. You may be sucking air thru the heater assy. Somewhere I have the part #s to rebuild the heater. I'll look for them if you want.

 

cause ok when i picked up my truck from the place that did the work for me. i had already 300 miles on the truck since i filled it and i had a quarter tank left. and on that last quarter tank i was able to get 150 miles out of it so a total of 450 miles on that tank and i had 3 gallons left in it. then i filled the tank back up and thats when the milage went down hill again and then i noticed that the fuel heater wires on top were burnt to a crisp.

that place changed the fuel filter for me. and he said that if any fuel got spilt on it that it could have burnt it out.

if that was sucking air into the system would it really but my MPG in like half of what i should be getting????

if u could find the part #'s that would be great. i found a later post and are these #'s the same??
heater element upper quad ring 3834185-s $1.95
heater strainer kit 3845400-s $6.42
heater element (with stat) 3907766 $35.18
cable harness 3843722-s $49.39

are the prices still the same as these????



so i am thinking that maybe the new injectors did help the milage and then when that heater blew its causing the bad milage again. but can it cause the mileage to be that bad??????

thanks

 

My trucks MPG droped off really fast one time and after doing a bunch of stuff to it I found out my lift pump was bad. replaced it and MPG almost doubled
DM01

 

how much was the lift pump and also how can u tell when it goes bad?? is there anyway to tell??

also ever since i bought this truck u have to crank it over like for 2-3 seconds before it will start. my 94 i had that i traded in for this one was getting 18.5-22 MPG and it would start right up.

thanks

 

Hey Joe can you put what truck you have in your signature ,it will get you better help when the guys know what truck you are working on.If your truck is a 94-98 check your fuel hose back behind the fuel filter they go bad and leak alot.Thats is what usually causes hard starting .

 

there is no fuel leaks anywhere. u can leave it sit on a dry floor all night long and it won't leak anything but a little oil here and there.

thanks

but i will check that fuel like and see. as maybe its mixing in with some oil before it hits the ground.

 

They say that the lines can become porous and suck air but not leak alot of fuel,They are so jammed back in by the firewall you can bareley even see them.There is even a special kit made by one of the vendors to replace them.They are a known problem you may want to check on.Its a good idea to change them before they give you trouble because if they start leaking bad your stuck on the side of the road and they are no fun changing them out on the road somewhere.I hope If they are bad it solves your problem.

 

if they were sucking air or the fuel heater housing is sucking in air. the truck shouldn't even run???? right????

or could it run and be causing the hard starting and also the poor fuel mileage?????


how do i check the lift pump anyone????

thanks

 

The truck can suck air and still run. The fuel lines will not necessarily leak diesel. Had this happen on my 96' 5spd. I don't see from the original poster if the current truck is auto or the tranny from the original truck. The auto's take an extra second to start. My 96' 5spd would start instantly once all the problems were fixed. I replaced the fuel supply/return lines which were dryrot. I also did the fuel preheater kit. Both of these helped the problem but didn't fix the issue. The bad part which many forget to check was the fuel preheater to lift pump soft line. Once removed it was very obvious this was the problem. Local DC dealerships had a back order on the fuel line. I already ran Coast Guard approved marine diesel fuel line. Marine fuel line is twice the thickness of standard fuel line. I ran a loop in the lift pump soft line to avoid putting a kink in the line. Once everything was back together truck never ran better.

I also bought a new overflow valve that had no effect.

 

the mileage is killing me.

anyone?????

thanks

 

Did the place that did your work for you check your fuel pressure? If it's low, you'll get a poor spray pattern out of the injectors that will kill mileage and power. Checking it will tell you if the lift pump has gone south since you've replaced the filter and O/F valve. How is your smoke situation? Too much black smoke on acceleration will hurt your mileage. You can back off the starwheel a bit to help control smoke. Do you know exactly what they did to "turn up" the pump? Slipped timing is very common. If they didn't get the gear and shaft perfectly clean and a new nut torqued up enough, it's a good chance it slipped again shortly after they started it.

You might want to check all your intercooler boots to make sure you don't have a boost leak somewhere. You can get a 4" ABS plug and drill it for an airhose fitting. Stick it in the hose going to the turbo and pressure it up to about 20 PSI. Then spray all the boots with soapy water.

Has the valve lash been set recently? It's questionable how much it would affect mileage but every little bit helps.

A slipping clutch/tranny will kill mileage too.

 

R-Joe - slow down a bit here - fill in your signature with your truck details, it's quite hard to help you diagnose without more factual truck data.

My truck is STOCK, as it was DESIGNED to be used. I average not less than 19 mpg around town, not over 25.2 mpg on the freeway (both figures unloaded, keep in mind this is a 2wd manual regular cab, as light as these trucks come.) While it is common knowledge that some modifications and timing advances could be performed without negatively affecting mileage, and in a few instances, mileage could actually improve, such as "free flowing" exhaust systems. However, as one who has performed flow dynamics on tubular devices such as exhaust systems, I also realize that many aftermarket companies offer lots of HYPE, little actual benefit.

The small leakage of air into the fuel return line is an actual sitaution that has affected my vehcile. I first noticed the problem after letting the truck sit for three months, it required manual priming to re-start. After about two weeks, in the middle of the day, with a two hour shutoff time, the engine refused to start at all - no fuel was getting to the pump. The lift pump had died, the lines (supply and return) had small air leakage, and the sender unit needed replaced.

For the interm, try pressing on the accelerator about 1/2" (no more...) as you crank the engine. As I do this, my engine will start in 1/2 sec or less. If I forget, it's 2-3 seconds like your truck. This was the case prior to and after the fuel system repair I just mentioned, as well as the five years I have owned the truck.

If all else fails - take it to a good truck repair shop and let them do a thorough diagnosis, they should be able to help you get to the bottom of this.

Just a clarification...I'm not opposed to modifications - it may have sounded that way before. I just know that if you "play" with something that was designed to operate a certian way, you often wind up paying for it. Yes, these engines can take a lot. I choose to leave mine stock as I would like to still be driving it at 500k.

Good luck!