Diagnosing poor fuel economy..

[TX Gooseneck]

I just had the timing on my pump set properly. My fuel mileage is still in the dumps(around 15mpg)



Injectors shot? any ideas?

 

[cerberusiam]

Which truck, or is that a touchy subject?

 

[TX Gooseneck]

Which truck, or is that a touchy subject?

opps...

Long day. It's my 93 d-350

 

[cerberusiam]

Gear ratio? 4x4? Pump work? BOMB's? Need a little more info.

 

[tugboatphil]

Tex,



If you're running 3. 54 gears, I'm right there with you. I log my mileage and fuel whenever I fill up. I consistently run just below 16 mpg. I'm at the point of putting in better injectors, so I can let you know if it makes a difference.

 

[TX Gooseneck]

alright, full info - 1993 D350, club cab, dually, automatic, 4. 10 gears, 240,000 miles - mods, full boost, and off boost turned up, straight piped, and holesawed air box with stock replacement filter.



The mileage seemed to get a little better for a while (mid to high 16's) and has recently fallen again (before getting the timing reset).

 

[LEggers]

I can't keep my foot out of mine long enough to get a good number I am stuck in the gutter at about 12MPG.....

If I just took it easy I cannot see myself getting much better with POD's straight pipe and pump mods.



I have 3. 50's also but run a tire one size larger than stock. Some say this hurts me. I kinda agree with them.



Lance Seattle, WA.

 

[MFalkinham]

alright, full info - 1993 D350, club cab, dually, automatic, 4. 10 gears, 240,000 miles - mods, full boost, and off boost turned up, straight piped, and holesawed air box with stock replacement filter.



The mileage seemed to get a little better for a while (mid to high 16's) and has recently fallen again (before getting the timing reset).

That's about the fuel mileage that I've always gotten with mine (14-15mpg), granted mine is 4wd and unbombed but the rest seems the same.



- Mike

 

[cerberusiam]

Injectors could probably use a tune up if they have never been touched. The auto doesn't help and the older it gets and the more power you throw at it the worse it gets. Mine took a dive to around 16 to 17 after I replaced the pump and didn't do injectors. Converter is on its way out also. The larger tires I run cut the rpm's down some but not sure it helped mpg. With the 4. 10's unless you run some taller tires 16 mpg may be about right



Of course the largest variable in the whole mix is your right foot and how it is applied to the throttle pedal. Injectors would be a good place to start, possibly a converter next. The cheap test is driving habit modification.

 

[TX Gooseneck]

Convertor is brand new. This truck is meant for highway commuting if my old man is borrowing my 04. Pretty much stick it on cruise and roll at 75.

The 91 gets 19-20 and is pushing 400,000 miles, granted it's a reg cab, but the injectors have never been touched and it has the same 'mods'

 

[TX Gooseneck]

edit, the 91 does have 3. 54 gears

 

[LEggers]

Goosneck

I think it is a weight issue allong with the extra width from the DRW.



I wanted better MPG when I got my truck also but after talking to others it just seams the DRW 350 is a wind drag weighted monster.



Mine is also 4x4 auto.

 

[LEggers]

Give you another example.

In Spokane, WA. with no wind and at 1800-2000 ft I ran a 16. 41 in the 1/4 mile.



Fast forward a month at sea level differant track I ran a 17. 5 with a 5mph head wind. I thought I could get under 17's all day but becasue of the slight wind it was not going to happen...

 

[TKingsbury]

You say you want to get on the freeway and cruise at 75 with 4. 10s! That seems awfully fast. What's your rpm @ 75 with each truck? I bet if you slow down, your economy will go up alot. Slowing from 80 to 65 was worth about 3 mpg on my truck. I think mine was due to wind resistance, it's kinda high.

Travis. .

 

[cerberusiam]

The extra tires make a difference in wind resistance and rolling friction but I suspect the 4. 10's have a much larger impact. For mpg they definitely were not the best option. Couple that with a fluid connection and a loose converter and it gets worse. Is the converter a new stock unit or a new unit with better fluid coupling? Stock they were only about 70% efficient and adding extra resistance didn't help.



Too many differences between the trucks for a fair comparison. At anything over 120k the injectors are more than likely starting to degrade. Trying to compare mpg based on mileage on injectors is inaccurate with similar trucks let alone the differences in these two.



Since the mpg has started to decline something is affecting it. Could be injectors, could be the injection pump, could be the quality of diesel your getting, could be the trans.



The mileages on both trucks seem to be inline with what most others are getting so you can start swapping parts or drive the 90. Its all a matter of personal preference.

 

[DPetrey]

I have a 92 W-250 4x Auto stock everything in town i am getting 17. 5 stock injectors i want more i have good fuel and Air but am thinking about new injectors and a mild pump tweak but don;t know how and don't want to mess anything up cause i will have to wait a month for parts and Napa here lokks at you cross eyed on any diesel parts. By the way does anyone know the tolerences for the turbo axail and thrust i have . 022 axial and . 012 thrust i can do the center se3ction my self just need part # if possible

Don Petrey

Alaska Marine Highway System

 

[Hunter4x4]

You've probably seen my other thread on turbo bark - still not done over there! Looks like some more questions need to be answered and discussed!!



Anyway, I was going to ask about fuel economy after the turbo thread ran its course but this one was already up!



I've heard a lot of stories about fuel mileage in the mid and low 20's , and thought I had a problem. But after reading the foregoing page and a half of posts I'm thinking that maybe I don't have a problem. In addition to what's in my signature below, I'm running an A518 transmission and 3. 55 gears. I get mid-16s for the post part, dipping to 15s around town and going up to maybe 19 on an easy hiway run.



Towing a 6,500 pound trailer (in 3rd, not OD) I'm getting a very consisten 11. 0 - 11. 1 mpg.



So it kind of looks that I'm in the ball park, eh?

 

[tugboatphil]

On this same topic, what effect does a taller tire have on odometer mileage? Does it indicate more miles travelled or less? Perhaps I've been figuring wrong the whole time.

 

[DSteimle]

Mileage

my dead stock 93 d350 with 5-spd and 3. 54 gets steady 18. 9 mpg- on long interstate runs with cruise set at 2100 rpm have gotten 22. 5

daryl

 

[DanWilson]

miles per gallon

I realize I may be putting this in the wrong place, but here is some info for thought. I purchased my truck on Memorial Day weekend, since then I have added fuel 20 times (refill at 1/2 to 1/4 tank). Fuel prices were $1. 53 back then, this morning I paid $2. 04 At first I ran 65 mph during my 50+ mile daily commute and got 14. 5 mpg, then I eased up above 15, then in the mid 16s. Three tanks ago, I hit 16. 9, tank before this- 17. 1, this morning 18. 353mpg. The only things I have done is put a Fleetguard BHAF on a few weeks after the purchase, added Royal Purple 15w-40 3188 miles ago, and added 1gal of wmo to the tank at the last fill up. I keep it between 60 & 65 and I never rev it more than 2000 rpm unless I have to get out of somebody's way, that includes all shifts at or below 2000. I think the right foot has the largest impact on fuel mileage. My $0. 02 Dan