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Discussion Starter · #1 ·
Have a 99 7.3 F350 I get 11 mpg empty or loaded with 15000 lbs. Originally was getting 16 to 18 and suddenly dropped. Already replaced injector orings, No codes, turbo spins freely. Intake open and does not smoke. Help quickly.
 

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More information on the truck?

Oil change? other changes?
 

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You'll want to post the gear ratio of your rear end.

You will definitely want to check for sticking brake calipers and/or slides. You should also check the EBPV and its sensor, you'll want to check for exhaust leaks up to the turbo, and for leaks somewhere in the intercooler or it's tubing.
 

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Check your rear differential and make sure it is filled with gear oil. I'm fighting low fuel mileage right now also. Mileage started at 15.3 MPG when I bought the truck 3 April. Dropped down to 13 MPG after a couple of weeks. I found out that the pinion seal had leaked out 1/2 of the gear oil long before I ever bought the truck. I just got the joy of having to replace both pinion bearings and the two side bearings ($1,000 or so). That brought me back up to 15 MPG.

Still looking for the rest of my mileage. I'm hoping to get up into the 17+ range before I start modifying the truck.

It is going in tomorrow to have the brake lines flushed and the brakes inspected. He is also going to check all four wheel bearings to see if any of them are bad.

-Jim
 

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Mines doing the same thing,,,,, Me I think it's the fuel
 

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Even with the new fuel that is on the market with the upgrades and additives my
"Flying Brick" is in the range of 18mpg
 

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Discussion Starter · #8 ·
Oil change every 5000 miles. Has been a problem for quite awhile now. Exhaust back pressures are normal. Gear ratio is 3.73 with an auto trans.
 

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Have you ever installed a new brake hardware kit and new slide pins and new brake lube? If you did, did you completely clean out the bore that the slide pins go into?

Does the truck lack any power? I would still check the EBPV.

You might check and see if the 99's were affected by the cps recall. I think grey = good and black = bad. Blue should be good too.

It may be a combination of a few things. You should at least be over 15MPG.

There are tons of articles on here about this subject. I was able to get mine up to 15.8 MPG and I'm still doing stuff. I think i'll be over 16 MPG by next week.
 

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I too am battleing this issue. I bought the truck last summer and put 35's and a programmer on it soon after. I got a steady 18 on the highway. All of the sudden right around christmas time my mileage dropped, after a recent new transmission. I blamed it on winter fuel, well summer is here and I'm still getting 13 on the highway, even less city. No changes have been made accept for a dp tuner instead of my superchip. I have had all codes scanned, ebpv sensor scanned, replaced cps, injectors buzz tested, NOTHING TO BE FOUND. I have my truck in the tranny shop right now seeing if my torque converter has been slipping and that would account for my fuel mileage. When it gets out I also am going to replace the icp, there was some oil in it. Maybe one of these two things will be the fix, but I am doubting it. I have had horrible luck with the dealership so taking it to them to have parts thrown at it for thousands in hopes for a fix is not an option, I am quite frustrated here.
 

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Discussion Starter · #11 ·
I have gone through the brakes, front and rear. The engine has the grey cam sensor. Truck has full power. I do have a superchip and 4 inch exhaust on it, but the problem was there before.

Have you ever installed a new brake hardware kit and new slide pins and new brake lube? If you did, did you completely clean out the bore that the slide pins go into?

Does the truck lack any power? I would still check the EBPV.

You might check and see if the 99's were affected by the cps recall. I think grey = good and black = bad. Blue should be good too.

It may be a combination of a few things. You should at least be over 15MPG.

There are tons of articles on here about this subject. I was able to get mine up to 15.8 MPG and I'm still doing stuff. I think i'll be over 16 MPG by next week.
 

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Trans ? Was it a rebuild? or new?
Is it shifting at different rpms from before?
 

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Ok, when you change your oil, have you ever changed the oil in the high pressure reservoir? If you don’t change that oil too, I would start changing it. www.powerstrokehelp.com has videos on how to do that. Advanced auto has a hand pump that is red with some orange hoses. Make sure you get the oil treatment he shows you, I think it’s called ProLong, and use it the way he shows you. Autozone and Advanced Auto both should have it. Don’t get the smaller “booster” bottle. You have to get the big bottle. Run injector cleaner too. Bill recommends Stanadyne, but I just buy a bottle of Lucas when I get the ProLong because you probably won’t find Stanadyne at a parts store. You may already be running injector cleaner.

Torque converter is a good think to check, but I would think the slippage would be noticeable and you would see junk in your trans pan. IMO the mileage would be worse the heavier you are.
 

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If none of the things i have mentioned help your truck, you have different problems than i have had. I have seen increases with most everything i have mentioned.
 

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Ok, when you change your oil, have you ever changed the oil in the high pressure reservoir? If you don’t change that oil too, I would start changing it. www.powerstrokehelp.com has videos on how to do that. Advanced auto has a hand pump that is red with some orange hoses. Make sure you get the oil treatment he shows you, I think it’s called ProLong, and use it the way he shows you. Autozone and Advanced Auto both should have it. Don’t get the smaller “booster” bottle. You have to get the big bottle. Run injector cleaner too. Bill recommends Stanadyne, but I just buy a bottle of Lucas when I get the ProLong because you probably won’t find Stanadyne at a parts store. You may already be running injector cleaner.

Torque converter is a good think to check, but I would think the slippage would be noticeable and you would see junk in your trans pan. IMO the mileage would be worse the heavier you are.
That guy that puts out those"7.3 help videos" is an idiot, He has been proven way wrong on a number of things that has to do with some expensive repairs...(possible mistakes if its done wrong),I wouldn't pay him any attention....Just my .02 worth
 

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That guy that puts out those"7.3 help videos" is an idiot, He has been proven way wrong on a number of things that has to do with some expensive repairs...(possible mistakes if its done wrong),I wouldn't pay him any attention....Just my .02 worth
I've caught a few things he said, and thought NO!!!! But alot of the stuff he shows in the videos is Awesome to see because you can't find actual video anywhere else. Everyone has their own opinions, that's ok. I know for a fact that the oil in my high pressure reservoir was gunky. So i flushed it out pretty close to the way he shows. I kid you not the truck came alive and i gained an extra MPG. If changing the oil in the high pressure oil reservoir is wrong, i will vanish from this site for ever. It's the best thing i've done so far, second is the brakes.
 

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Seems to know his stuff imo and Ive talked to him quite a few times, lot of happy people around here in (atlanta) have used him.
 

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I too changed the oil in the high pressure reservoir and mine was like GLUE!!
 

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How much oil is in the HP resevoir? Does it recirculate with the rest of the engine oil, or is it trapped there? Also, is there a way to test the cetane in the fuel that we are forced to use. My mileage has suffered in the last couple of years, and I believe that it is in large part due to the fuel. I have gone from around 19.5 to 17.4 on my '02 F-350.
 

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Im sure you could send it to one of those labs that will test your oil but someone else knows better than me. There is I believe about 2 qts. in the reservoir. It is supposed to circulate but It often doesnt, so a lot of times most of the same oil is in there for a VERY long time. According to Bill, changing this oil separately is crucial to the life of your injectors.
 
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