A co-worker purchased a 93 and is concerned about the mileage.
The following is the email I got from my co-worker:

I replied with the following questions:
1) How are you guys on maintenance? (Air filter, fuel filter, trans filter, oil changes, etc).
2) What have you done to the truck since its purchase? (New/larger tires? Add a shell? etc).
3) How long have you had this truck? I ask because, as you probably know, winter diesel is a different blend than summer diesel. Im not saying that this is your problem, but it may contribute.
4) Hows the "over all" power?
5) Smoke at all (More than it should)?
6) How's she start? Does it take more cranking than it should?
7) Notice any leaks, wet hoses?

The answers:
So I ask you guys:
Could the tire size increase be throwing off the calculations?
Do these trucks have cats?
Transmission slipping?
What do you guys think?

I appreciate the input guys.

Thanks
Rich

 

I'm not the sharpest guy on here and am just learning diesels myself but I've been told by my injection guy that the injectors wear out at 150,000 or so give or take. Mine were popping 750 psi early before they reached full atomization pressure. That was the issue with mine getting poor milage.

 

Thanks spunbearing.
When this happend, did you notice any other side effects beside the poor mileage?

Rich.

 

Some random thoughts re mileage. 15mpg, city driving? Short runs? or is it a decent commute? I've always got 20+ with mine, but its only run when its gonna be running a while. Never just run it the 4 blocks to work and short stuff like that.
Short runs will kick the snot out of fuel mileage, as will stop and go obviously.

Tire size increase will of course mean the speedo shows slower than true, but I'm not sure what the % would be. Maybe its not getting into OD. top speed would be 65-70mph in direct.

No cat on mine, I think CDN trucks are Calif. emissions.

Has it ever had a valve set? When I reset mine my mileage picked up. Not by a third, but about 1.5. A lot of people seem to think diesels are a run it forever all you gotta do is change the oil kinda thing.

Some thoughts for now. I'll keep puzzling but I know someone is gonna nail it. The sound you hear then will be me slapping my forehead. d'oh.
There is a LT285 85 R16 tire? Thats huge.

 

mine is right at 15ish all around MPG but i knwo my OD is off so im getting better than that, just havent figured out how much better.

 

the tire size would have some effect. You would be driving farther than what the odometer says. Time a mile or use a GPS to see how far off the spedometer is.

150K is nothing as far as milleage goes, just getting broke in.

And if that 15mpg is around town that is nothing bad like said above. I drive 24 miles one way to work but have several turns to make and some town driving at the end. I average 18mpg doing that. On a long HWY only trip I get 22-23mpg.

Mine drops 1.5mpg if I get blended fuel in it. I try to avoid it and put additive in #2 in stead.

 

Here's a bit more info about the tires and valves:
Rich.

 

altitude change??? Back home my 92 gets 17 in town and not much better on the highway (20 or so) but up here in Laramie (7200' and home is sea level) I get 12.6 in town (11.5 if I have the hubs locked) and I dunno what I get going to Cheyenne and back, btu I get 19-20 going to Denver... Got 12-14 coming out here towing a trailer with my Subaru on it (Guy I bought it form said the worst he ever got was 16 grrr) I knocked a good amount of dirt out of my air filter when I changed the oil and coolant at school, I need to replace the darn thing but the WyoTech parts house didnt' stock my filter :-( And my truck has stock size tires, and it does have a canopy but it's an aluminum one, and I didn't think that would cause a 5MPG drop in milege!

 

Do you get better mileage with a cap/ shell or open box? My mileage has dropped also - but my right foot has gotten heavy Still getting avg. 18-19mpg @ well above speed limit on hiway I gotta leave early for work before something happens

 

The main thing that I noticed was the poor milage and the truck shook at idle and vibrated. I took it in and had the injector pump rebuilt and modified and it ran great but the milage was still poor. We didn't think of injectors because of the low milage (98,000) at the time.

 

Thanks spunbearing.
I'll pass that along.

Rich

 

Part of my low mileage problem I'm sure are old injectors, over 200,000 hard miles. Check lift pump and maybe even fuel return valve (broken spring?). Holsteinman has a topper but claims good mileage. My Chevy gasser lost a mile or two with the topper. The larger tires may hurt the mileage a bit, but have they account for change in ratio?

 

My 93 250 when purchased got 19.5. after the pump was done it got 20.1 it calced to. The aluminum shell when would drop it 1mpg or so. The tires will throw it off some. Its mouse and rat season with all the rains, I would pull the air filter and check it fro a nest in the box. I have constant problems here in my vehicles. Heaters,aircleaners, under hood you name it. winter fuel will affect it also.

 

well the tire size if larger than stock will actually make the speedo slower and not give the correct mileage as the tire will actually be rotating slower and there for not give the proper mileage it to would be slow ( eg. 15 miles on the odometer may actually be 20 ) so this could be the reason that the economy seems bad it may not be. look to see what the manufacturer recomended tire size is and that may answer your question