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View Full Version : Anyone have a f 550 with a 7.3L?


Aaron Marshall
09-28-2008, 11:11 PM
I have an 01 2wd f550 with a 7.3 automatic. Since I bought it two years ago the best millage I have gotten with it is about 7.4 mpg. Does matter how nice I drive it, doesn't matter if I just drive in town vs. hwy. Air filter is good, it doesn't have a cat. converter, i did put a very mild chip in it, and no change. Fuel filter is new, etc. The only thing I can think that might be bad is the muffler might be pluged up but it seems to have full power? I also have a f350 with a 7.3 and that one will get 16-20mpg depending. There is a large difference in gearing. My f550 has 4.88 gears in it which in my opinion is stupid. I think I might regear it to 3.73s. What kind of millege are you guys getting out of the same truck.

TPendagast
09-29-2008, 12:06 AM
I have an 02 f450 with those gears!
GARBAGE
The gearing is the problem.
They dont do any better than the 3.73 gears its not like the 4.88 pull a house out of the ground or anything!

The 4.88 is a disaster!

I bet that is your problem, but even with the 4.88 gearing We still dont do that bad on fuel, maybe about 10-11.

Weve been talking alot about swtich those gears out and honestly we might have done that by now. Ill have to ask the tree manager than runs that truck.

hosejockey2002
09-29-2008, 12:40 AM
If you regear your F550 to 3.73 gears (if it is even possible) it will be a total dog and you'll probably wreck your transmission. Having said that, I think something is wrong with your truck getting that low of mileage. I've rented F550 dumps in the past (7.3L diesel with 6-spd manual) and have consistently got 10-11 mpg loaded. Heck, my gas V10 E450 motorhome with 4.63 rear end gears and little tiny 225/75 16 tires gets 7.5-8.5 mpg, and that's moving a combined weight of nearly 17000 lbs.

Like I said, your mileage is awfully low, but I don't think regearing to 3.73 is going to solve your problem.

Gravel Rat
09-29-2008, 01:01 AM
The tallest gear ratio I would go would be 4:30s any taller than that you might aswell junk the truck it will be useless.

You buy a F-550 truck what do you expect the mileage of a 4 cylinder.

Are you sure your calculating your mileage right. My F-450 which weighs 9400lbs empty with a 6.0 6spd I get 11mpg empty and 10 mpg loaded. My previous F-Superduty (OBS F-450) with 4:63 gears 7.3 PSD 5spd weighed 8300lbs use to get 12mpg.

Where I live there is very little flat roads mostly 8 to 10 percent grades with twists and turns.

Are you sure your brakes are not dragging and the transmission isn't slipping.

You should be getting minimum 10 mpg if the truck is running right.

TPendagast
09-29-2008, 01:20 AM
The 7.3 diesels of the 90s with the 3.73 would get 22 or better on the highway.

Something happened with emissions that dropped the fuel mileage dramatically after about 2001.

An 84 naturally aspirated 6.8 ford diesel will get 27 to 28.

I still think 10 to 11 mph on your diesel something is wrong.

BlackCloudDiesel
09-29-2008, 01:59 AM
It might be your fuel as well.... I seem to get much better milage with the BP Diesel then anything else. It costs a bit more but if I can get 3 to 4 mpg more on some trucks, I think its worth it.

02DURAMAX
09-29-2008, 02:07 AM
It might be your fuel as well.... I seem to get much better milage with the BP Diesel then anything else. It costs a bit more but if I can get 3 to 4 mpg more on some trucks, I think its worth it.

Now I feel like trying BP Diesel...:cool2:

Aaron Marshall
09-29-2008, 05:46 AM
If you regear your F550 to 3.73 gears (if it is even possible) it will be a total dog and you'll probably wreck your transmission. Having said that, I think something is wrong with your truck getting that low of mileage. I've rented F550 dumps in the past (7.3L diesel with 6-spd manual) and have consistently got 10-11 mpg loaded. Heck, my gas V10 E450 motorhome with 4.63 rear end gears and little tiny 225/75 16 tires gets 7.5-8.5 mpg, and that's moving a combined weight of nearly 17000 lbs.

Like I said, your mileage is awfully low, but I don't think regearing to 3.73 is going to solve your problem.

I can regear to a 3.73 gear ration, I just have to also purchase a new carrier for the gear set. I don't know why it would wreck the truck, I just got done driving a f350 drw with 3.73 gears (a 2000) and it got 13-15 mpg hwy. and it had plenty of power.

Aaron Marshall
09-29-2008, 05:49 AM
The tallest gear ratio I would go would be 4:30s any taller than that you might aswell junk the truck it will be useless.

You buy a F-550 truck what do you expect the mileage of a 4 cylinder.

Are you sure your calculating your mileage right. My F-450 which weighs 9400lbs empty with a 6.0 6spd I get 11mpg empty and 10 mpg loaded. My previous F-Superduty (OBS F-450) with 4:63 gears 7.3 PSD 5spd weighed 8300lbs use to get 12mpg.

Where I live there is very little flat roads mostly 8 to 10 percent grades with twists and turns.

Are you sure your brakes are not dragging and the transmission isn't slipping.

You should be getting minimum 10 mpg if the truck is running right.

4.30 gears wouldn't be a very significant change in engine rpm.
no i do not expect to get the millege of a 4cyl but 7 seemed a little low to me sorry for asking
brakes are not dragging, and the transmition is flawless.
I would be thrilled to death with getting 10 mpg, thats what I'm hoping to achieve.

Aaron Marshall
09-29-2008, 05:51 AM
It might be your fuel as well.... I seem to get much better milage with the BP Diesel then anything else. It costs a bit more but if I can get 3 to 4 mpg more on some trucks, I think its worth it.

I have also tried the bp premier diesel and that did nothing for me. I have a friend with a duramax and that seems to make a big difference in that engine but have not had any luck myself. They seem to run slightly better on that fuel though.
Thanks

Aaron Marshall
09-29-2008, 05:53 AM
I have an 02 f450 with those gears!
GARBAGE
The gearing is the problem.
They dont do any better than the 3.73 gears its not like the 4.88 pull a house out of the ground or anything!

The 4.88 is a disaster!

I bet that is your problem, but even with the 4.88 gearing We still dont do that bad on fuel, maybe about 10-11.

Weve been talking alot about swtich those gears out and honestly we might have done that by now. Ill have to ask the tree manager than runs that truck.

Let me know if you did this and to what ratio is was switched to, thanks much.

Aaron Marshall
09-29-2008, 05:57 AM
the reason I want to possible re-gear is the power stroke makes its top hp at 2600 rpm and top torque at around 2200 rpm. My truck hardly ever runs those rpm. Going 55mph my rpm is around 25-2600 rpm, i slow down going up hills w/trailer and skid steer because the motor is just screaming and has no torque in that range. This is why I think that re-gearing will help me out. btw in 2001 the only gears ford offered in this truck were 4.88 and 5.38.

TPendagast
09-29-2008, 10:57 AM
the reason I want to possible re-gear is the power stroke makes its top hp at 2600 rpm and top torque at around 2200 rpm. My truck hardly ever runs those rpm. Going 55mph my rpm is around 25-2600 rpm, i slow down going up hills w/trailer and skid steer because the motor is just screaming and has no torque in that range. This is why I think that re-gearing will help me out. btw in 2001 the only gears ford offered in this truck were 4.88 and 5.38.

Ouch! maybe thats a f550 thing huh?

Tree manager for my company dropped the whole rear diff and changed the gear ratio to 3.73.
Says it runs now just like the 1994 truck it replaced.
I remember that old truck, we called it the race truck because it was so fast and powerful. It got 17-20 mph.
So if re-gearing it made it work like THAT truck, the it was worth it.

IMO the 1994-1997 7.3 Fords were the best ever.

The F550 wasnt really a "good" truck until it started getting the black plastic dealies around the fron fender wells (not that has anything to do with the truck) which I think was 2004.

I remember our local nursery stayed away from them until then, because we were going to get a 550 and get rid of this 450 we had and they were like STOP NO DONT!

Then I laughed at them when they got on in 2004, but they explained to me the 550 had changed.

I see later 550's and 450s (2004-2006) and they are all sweet trucks, but then the drivers and mechanics do nothing but complain about that 6.0 sooooo personally Id stay away from Ford Diesels.

F250 or 350 with a V10 go for it.

Diesel? hmmm Id go medium duty honestly,check out cab overs or international 4300s - 4700s.

The whole idea of a pick up truck with a diesel engine trying to do the work of a truck bigger than it still freaks me out.

Essentially thats all a 450/550 is a Pick up on steroids.

For 50k + why not just buy a bigger truck? I know thats really hard in New York due to the CDL rating being 18,000 gvw.

But elsewhere it is usually 26 k gvw

TXNSLighting
09-29-2008, 12:45 PM
The 7.3 diesels of the 90s with the 3.73 would get 22 or better on the highway.

Something happened with emissions that dropped the fuel mileage dramatically after about 2001.

An 84 naturally aspirated 6.8 ford diesel will get 27 to 28.

I still think 10 to 11 mph on your diesel something is wrong.

a 6.8? you mean 6.9 and they didnt get that good...

TXNSLighting
09-29-2008, 12:51 PM
Ouch! maybe thats a f550 thing huh?

Tree manager for my company dropped the whole rear diff and changed the gear ratio to 3.73.
Says it runs now just like the 1994 truck it replaced.
I remember that old truck, we called it the race truck because it was so fast and powerful. It got 17-20 mph.
So if re-gearing it made it work like THAT truck, the it was worth it.

IMO the 1994-1997 7.3 Fords were the best ever.

The F550 wasnt really a "good" truck until it started getting the black plastic dealies around the fron fender wells (not that has anything to do with the truck) which I think was 2004.

I remember our local nursery stayed away from them until then, because we were going to get a 550 and get rid of this 450 we had and they were like STOP NO DONT!

Then I laughed at them when they got on in 2004, but they explained to me the 550 had changed.

I see later 550's and 450s (2004-2006) and they are all sweet trucks, but then the drivers and mechanics do nothing but complain about that 6.0 sooooo personally Id stay away from Ford Diesels.

F250 or 350 with a V10 go for it.

Diesel? hmmm Id go medium duty honestly,check out cab overs or international 4300s - 4700s.

The whole idea of a pick up truck with a diesel engine trying to do the work of a truck bigger than it still freaks me out.

Essentially thats all a 450/550 is a Pick up on steroids.

For 50k + why not just buy a bigger truck? I know thats really hard in New York due to the CDL rating being 18,000 gvw.

But elsewhere it is usually 26 k gvw

Man you are scattered! And actually it was 95-97 was the best years. 94s were pretty terrible. well the second half. The very first powerstroke.

But yeh that is a little low but comeon its a 550. Id be happy with 8mpg. You can tow anything with that truck. Maybe try 4.30's.. How about an air intake? Those help.

Gravel Rat
09-29-2008, 05:30 PM
I forgot all about that the 99-2001.5 F-550s had the Dana 135 which is a monster axle for a truck that size. I can see limited gearing options I know the newer F-550s have more gearing options.

TXNSLighting
09-29-2008, 06:32 PM
I forgot all about that the 99-2001.5 F-550s had the Dana 135 which is a monster axle for a truck that size. I can see limited gearing options I know the newer F-550s have more gearing options.

Those Rear ends were a PAIN to replace to!! Took three guys to do it.

Gravel Rat
09-29-2008, 07:37 PM
Ya they are heavy rear axle it is definatly overkill for a F-550 I can't remember correctly but the rear axle holds 3-4 gallons of 80w90 :dizzy:

cutbetterthanyou
09-29-2008, 08:12 PM
Before you spent alot of money i would take it to the dealer and get them to plug it in to the computer and make sure everything is running right and there are no bad sensors

CAT powered
09-29-2008, 08:16 PM
Check your Exhaust Backpressure Valve. It could be blocked with soot and that could be killing your mileage.

Here are instructions on how to clean the tube out.

http://guzzle.rbmicro.com/ebps.html

TXNSLighting
09-29-2008, 08:21 PM
Ya they are heavy rear axle it is definatly overkill for a F-550 I can't remember correctly but the rear axle holds 3-4 gallons of 80w90 :dizzy:

I believe that is correct!

TPendagast
09-30-2008, 01:51 AM
a 6.8? you mean 6.9 and they didnt get that good...

Yea 6.9 and no Im not that confused, I saw and witnessed the naturally aspirated for diesel get that good (there were NO emissions on those engines back then) it was in a single cab pickup, no dump, duallys no weight really to speak of, real light truck. The guy drove it back and forth to work for two weeks on one tank of gas 6 days a week, thats what made us do the math on it to figure out what is was getting.

I used to work for Tru Green back in the 90s and we had a ton more diesel fords than just about any other company possible. They all ranged from 93-98 and the 94-97 trucks were the best and all basically seeemed to be the same truck.
97 was the first year the f150 looked like a different truck than the 250 and 350s as it was more "explorer" than it was pick up truck.
93 was the really bad year for diesel in the Ford fleet, every 93 we had was a dog.
We also have that era to thank for the e40d tranny that belonged in an explorer and found its way all the way up to the f-superduty.

E40D and its legendary torque converter with the four wimpy spot welds.