fuel mileage queston

[Lobanz]

I bought my 93 7.3 IDI 4x4 F250 (ext cab, full size bed, no turbo, 285/75R16 AT tires) a couple years ago and got 19.5 mpg on the way home keeping at 55 mph (~75 mile or so IIRC). Then I had a new IP and injectors installed (at very reputable diesel shop) and have never got that mpg again. Mechanic said he "turned up the pump just a little", but I'm not sure that has much to do with it.

But my MPG seems to be all over the map, but I don't check it unless I'm on a little road trip. Track miles with GPS since PSOM is shot (no speedo or odo). I just fill up the tank till I see diesel in the fill neck. Then when I get back, I fill it up the same way. I always keep both tanks completely full. Use Power Service Diesel Clean in it. Truck does not have a tailgate. I usually drive with all the windows open unless its raining or too cold.

I recently drove 100 mi round trip to pick up feed. Drove back with ~2000 lb in the bed and got 15.4 mpg. Not too bad.

Then, I drove about 150 miles round trip (in heavy rain most of the time) and only got 12.5 mpg.

One difference was that on the first 100 mile trip, I did my best to keep it under 55 mph (using GPS speedometer app on my phone). The second 150 mile trip I wasn't as particular about keeping 55 or under, but I did drive kinda slow because of the rain -- sometimes 35 mph, sometime fast because the rain slacked up.

I think once you get over 55 mph, your mpg goes downhill fast.

 

[nelstomlinson]

I'm not sure what the rear end ratio is in my '89 crew cab. It hits about 50mph in 4th gear at 2,000rpm with stock tires.

We did a 1,000+ mile road trip this summer with a light camper in the back and an 8,000lb trailer behind. We cruised at 55 on flat ground, and kept it around 2,500rpm on the hills. Sometimes that had us in third gear, sometimes in second. On the downhill runs we sometimes got into fifth.

The worst mileage we got was about 11, from Fairbanks to Denali with strong headwinds. The best we got was about 14, coasting downhill from Denali to Anchorage. Anchorage to Seward to Anchorage we got about 12.

Running empty back and forth to Fairbanks, we run at 65mph in fifth gear at about 2,500rpm and get about 15mpg.

 

[genscripter]

I think once you get over 55 mph, your mpg goes downhill fast.

That is precisely the truth. 55mph is the ideal for preserving MPG with an IDI from my experience. I used to be able to drive 55-60mph all the time before I got my turbo. However, once I put the turbo on, it's just too much fun to drive like a bat out of hell, especially here in California where 80mph is pretty much the norm on the highways.

The only times I keep it under 60mph is when I'm on some remote 2-lane road in the desert or Canada, where the conditions are not good for high speeds or there are lots of large animals wandering in the ditch. When I drive on these roads, I can get a lot better MPG.

However, even driving over 75mph, with all my efficiency mods, i can still get 17mpg. I just did a 12,000 mile trip in July, and the overall average was something like 17.1mpg. That's the only way you can get a long-term efficiency measurement. Measurements that are under a few hundred miles are not a good assessment of the overall efficiency of the IDI.

 

[genscripter]

I'm not sure what the rear end ratio is in my '89 crew cab. It hits about 50mph in 4th gear at 2,000rpm with stock tires.

We did a 1,000+ mile road trip this summer with a light camper in the back and an 8,000lb trailer behind. We cruised at 55 on flat ground, and kept it around 2,500rpm on the hills. Sometimes that had us in third gear, sometimes in second. On the downhill runs we sometimes got into fifth.

The worst mileage we got was about 11, from Fairbanks to Denali with strong headwinds. The best we got was about 14, coasting downhill from Denali to Anchorage. Anchorage to Seward to Anchorage we got about 12.

Running empty back and forth to Fairbanks, we run at 65mph in fifth gear at about 2,500rpm and get about 15mpg.

That stretch between Anchorage and Fairbanks is really nice. Denali is great too. I don't like the park's rules (no drive-ins) but we hiked up to the foothills of the mountain. Got a good picture of the peak before the fog rolled in. Saw a grizzly about 50 yards away on our hike. Thankfully he was focused on berries and didn't bother us. It looked like a volkswagon with fur.

 

[nelstomlinson]

Saw a grizzly about 50 yards away on our hike. ... It looked like a volkswagon with fur.

And teeth, and claws.

 

[Duke57]

I have a 92 7.3na with 4:10 rear and get 20 gallons to the mile. Oh well, pulls good!

 

[genscripter]

20 gallons to the mile.

 

[Duke57]

Well, it isn't that bad. My daily driver and drive it all day long, mostly city driving. And it's a ZF5 to boot.

 

[nostrokes]

I have a 92 7.3na with 4:10 rear and get 20 gallons to the mile. Oh well, pulls good!

Sounds like my 88 gasser!!

 

[Cubey]

Unknown miles on my original engine, due to 5 digit odometer but let's just guess 147,***.

6.9 NA, C6, 3.55

I get about 10.5 city/14-15 highway with a semi tall camper shell full of gear plus a hitch box. I carry 15-20gallons of water and about 2.5 gallons of gas for my generator. Plus tools, including a 3 to floor jack. Plus a 30lb LP tank.

If you check my fuelly, the huge drop until recently was pulling a 27ft trailer full time. The huge jump last month was after it was gone. I did some IP timing adjustment a few months ago but without any equipment, it did slightly help for towing power and I left it alone since mpg didn't suffer and it runs fine.

http://www.fuelly.com/car/ford/f-250/1987/cubey/555168

 

[Cubey]

91 ex. Cab 4wd e4od 4:10 gears 13-14 is the best I've ever seen in 3 years, and it has a turbo too. The guy I bought it from said he was getting 17 but I don't know how guess my foot is a lot hevier than his...

People say insane things when selling vehicles. A woman I bought a car from said the non-existent A/C system (had heat/vent only) would explode if charged, according to her mechanic.

 

[jayro88]

e250, 7.3NA, 3.54's, c6+DNE2 OD. I am pretty sure I cooked my OD control box on my last long trip towing my trailer. hours on end running at 1000* egt's and now nothing seemd to happen when I press the shift button.

With the O/D I would rang between 15.5 and 19 mpg. Without it I get between 14-16.5mpg. Towing my 30' TT with a full water tank I get about 10-12mpg depending on about a million variables.

 

[ABNORDY]

Ok guys , I got my '89 back up and running. did a little 150 mile jaunt down the road and back as we say in Texas. My questions is what kind of mileage are yall getting? My 7.3 with 4.10 and 5 speed manages 14 at best. Ive heard these engines can do a lot better, but how???? is it possible?? Give your results and what you did to achieve your mileage claims! Got pictures of the old girl coming up soon!

Not sure really, my gauge is either full or 1/4 tank. I must fill up at 400 miles because at 410 it's out of fuel and gotta crack the injector lines open, fill the filter and recharge batteries a couple times to get it going. I have not switched over to the electric pump setup as the cost for mechanical pump was like 25 dollars.

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[Andrew Fort]

I have a 7.3 na with a zf5 and 4.10s I believe. It hasn’t been running for 6 months until just this week. Right now I’m sitting at 97 miles and a half a tank down from completely full.


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[ttman4]

'90 F350, 7.3, ATS 088, cc dually, 5 speed, 4.10, 130 gal bedtank, 4 boys,...oh & the wife.

When this truck was new I'd get 18-22+ mpg cross country keeping it pulling, not hotroddin. Build a fire & keep it pulling 55-65 on flats & hills, 70-80 down hill.

At about 80K miles my mileage be down to about 14 or less. Pull the pump & injectors & have them rebuilt & mileage back up to 18-22+, At about every 80K miles I'd do this.

BTW, in early-mid '90's I had couple places in Tx I had rebuilds done....cost me then around $250-$350-$400 for pump & injectors....sigh