2001 Bad Fuel MPG Problem 6-9MPG

[Get Lucky]

So here is the Problem. We took a trip Form Wyoming to Minnesota. The first tank in both directions got about 10mpg but after that it went down to 6 one tank and another was 9 and another was 8. It seemed to be all over the place. On the trip we were hauling about 1200lb in the box and a trailer that was 4300lb. Max. the trailer was a enclosed deck over so it was for the most part just a sail with a v-nose.

The real problem is that the truck should be getting around 15-18mpg. In the past meaning that when it hauled two horse in a trail it would get 15-16mpg all highway.

Thing We noticed when pulling was that when we would hit grade it would just fall flat on it's face meaning that it wouldn't gain any speed up hills. We would enter the hill at 75mph and by the end it would be at under 60mph. We are only talking about maybe a 1.5 to 2% grade nothing major.

The only thing that have ever went out on the motor was the cam sensor, full wiring harness(warranty leaking battery ate it), two alternators, starter,and someone forgot to tighten the oil plug and it dump 4 gallons on the highway.

The only time this truck gets used is to haul, so it's not like we get any straight highway miles to look at.

This is completely stock other than a Bullydog tuner we put on to try and get better fuel mileage and to track a few things on the way home.


Please refrain from turning this thread into"well my truck gets this". I see that is almost every thread that I have read on the different forums it doesn't help and only takes from the topic at hand.

Thank you in advance for your help,
Kyle

[jesilvas]

Hand calculated?
low boost caused by many things would be first on the list

I made my Samsung SGH-I997 send this.

[Get Lucky]

yes hand calculated,

boost was 5-8 threw the flats of Nebraska and would run up to about 14-18 threw the grade. I only know this for the way home because we got the programer before our return trip trying to get better mileage.

I also have to say that the mileage didn't get better when we had the tuner on tow mode.

[Turbostang500]

did you check for a brake hanging up on the truck or the trailer?
Not a whole lot of reasons to lose that much mileage and still have good boost numbers.

I would also have it scanned for any soft codes in the PCM.

Also, you never mentioned if the truck seemed to be running correctly as in, no misfire. I would assume that if it was you would have mentioned it but since this is an online forum and I am not standing there, I have to ask some "dumb" questions.

Other info I would like to know is 4X4 or 2X4, auto or manual, and date air filter was replaced?

[CowboyCody]

leaking up pipes might cause a drop in mileage, but im not sure that much.

[Get Lucky]

Originally Posted by Turbostang500

did you check for a brake hanging up on the truck or the trailer?
Not a whole lot of reasons to lose that much mileage and still have good boost numbers.

I would also have it scanned for any soft codes in the PCM.

Also, you never mentioned if the truck seemed to be running correctly as in, no misfire. I would assume that if it was you would have mentioned it but since this is an online forum and I am not standing there, I have to ask some "dumb" questions.

Other info I would like to know is 4X4 or 2X4, auto or manual, and date air filter was replaced?

The brakes are not hanging up. It rolls way to easy on any incline always have to set the ebrake or will roll away.

It's heading to a friends shop on Friday and will throw it on a scanner to see if it will pull code.

It is a 4X4 and a Manual. The air filter was replaced think two years ago. really only has maybe 7k mile on it. When I inspected the air filter the top of the fins were dirty but the root of them was spotless.

Originally Posted by CowboyCody

leaking up pipes might cause a drop in mileage, but im not sure that much.

It has a small up pipe leak meaning I can hear the tick of the exhaust. I really don't think that it is bad enough to create this bad of mileage tho. We have two 2001 7.3 and they both have a small leak. The other one is still getting 12-13 pulling the same trailer.

[Turbostang500]

I don't think it is an up pipe leak. I have the usual ticks and boost numbers and MPG's are good still.

You never noted how the truck ran other than no power.

Maybe check your sensor outputs through the scanner and see if they are reading right. Something like the ECT, EOT, ICP could be wrong and messing with the PCM causing a defueling. I would think this would set the CEL but might not. Speaking of, does the CEL come on when you first turn the key on?

Another thing, did you happen to notice how much wind was present on that trip and what direction like head wind or tail wind? A stiff head wind will drop MPG's in a hurry!

[Get Lucky]

Originally Posted by Turbostang500

I don't think it is an up pipe leak. I have the usual ticks and boost numbers and MPG's are good still.

You never noted how the truck ran other than no power.

Maybe check your sensor outputs through the scanner and see if they are reading right. Something like the ECT, EOT, ICP could be wrong and messing with the PCM causing a defueling. I would think this would set the CEL but might not. Speaking of, does the CEL come on when you first turn the key on?

Another thing, did you happen to notice how much wind was present on that trip and what direction like head wind or tail wind? A stiff head wind will drop MPG's in a hurry!

Sorry about that.

Truck runs great. idles fine. start every time (always have cycle the plugs) other than the fuel mileage and lack of power it seems fine.

[85_305]

Originally Posted by Get Lucky

The brakes are not hanging up. It rolls way to easy on any incline always have to set the ebrake or will roll away.

It's heading to a friends shop on Friday and will throw it on a scanner to see if it will pull code.

It is a 4X4 and a Manual. The air filter was replaced think two years ago. really only has maybe 7k mile on it. When I inspected the air filter the top of the fins were dirty but the root of them was spotless.



It has a small up pipe leak meaning I can hear the tick of the exhaust. I really don't think that it is bad enough to create this bad of mileage tho. We have two 2001 7.3 and they both have a small leak. The other one is still getting 12-13 pulling the same trailer.

If its got an upipe leak, then of course you will be losing mpg.. your pissing your hard earned boost and fuel to atmosphere.

[Get Lucky]

Originally Posted by 85_305

If its got an upipe leak, then of course you will be losing mpg.. your pissing your hard earned boost and fuel to atmosphere.

Boost is not hard earned it's free power for the most part. The leak will be fixed in due time. I know we have another problem that is much worse. That is the problem I need to get fixed. Leaking up pipes might make up for maybe 2mpg at most not 6-7mpg. that I have now.