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Discussion Starter · #1 ·
You can read my set-up in my signature. I am currently running PHP tuner in daily driver. Mileage was checked by miles driven/fuel consumption (not off the computer) while driving like an old lady. My speedo is within 1 mph at 65 mph.

My normal commute to work and back in mainly 35 to 45 mph driving and I regularly get 12 mpg.

I recently pulled my boat on a 400 mile round trip to Lake Erie and back. This is a great test for towing because 99% of the trip is dead flat with no hills. I averaged 10 mpg. Never went above 65 mph. My boat is roughly 5000 lbs. and I was using the 80 tow tune.

Don't know if this is related but lately I have been experiencing hard starts in the morning. Had to crank on it 4 different times this morning before it would fire up. Have also noticed on a couple occasions that immediately after start up when I first go to pull away, the truck has absolutely no power and will hardly accelerate. After I get rolling about 75 yards it comes to life.
 

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Discussion Starter · #2 ·
Dang no help at all? I'm not feeling the love over here.
 

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Twitch
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First, about your fuel mileage....pullin a 5k boat even with a tow tune...your goin to see a slight fuel mileage decrease. Plus your truck being lifted decreases it even more. I would say thats pretty decent for pullin 5k and having a lift n tires.Your daily commute of speeds ranging from 35-45 mph is probably a lot of stop n go. This isnt helping either. To get a good shot at fuel mileage you need to be goin 50+ - 65 mph. Get on the highway with no load on your normal chip setting, set the cruise at 55-65 and burn a half tank or whole tank...depends on you. Then figure your mileage. Also keep your shift points and rpms around 2k, this will help you get the best mpgs.

Second, your hard starts in the morning...dont quote me on this but it could be bad Glowplugs or Glow plug relay. You should check them.
 

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Discussion Starter · #4 ·
First, about your fuel mileage....pullin a 5k boat even with a tow tune...your goin to see a slight fuel mileage decrease. Plus your truck being lifted decreases it even more. I would say thats pretty decent for pullin 5k and having a lift n tires.Your daily commute of speeds ranging from 35-45 mph is probably a lot of stop n go. This isnt helping either. To get a good shot at fuel mileage you need to be goin 50+ - 65 mph. Get on the highway with no load on your normal chip setting, set the cruise at 55-65 and burn a half tank or whole tank...depends on you. Then figure your mileage. Also keep your shift points and rpms around 2k, this will help you get the best mpgs.

Second, your hard starts in the morning...dont quote me on this but it could be bad Glowplugs or Glow plug relay. You should check them.
I can only get about 15 mpg on the highway. I realise all above what you said but even so it should get better than what I'm getting and 10 mpg towing 5K sucks for a diesel.

As for hard starts...I replaced the GPR yesterday so will see if that helps.
 

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Bigfoot is an OBS
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Start by checking the easy things:
-Oil, make sure it's diesel rated and fairly new. Most guys can't run over 5000-6000 miles without having some trouble.
-Check for boost leaks. Boost leaks are wasted power. The turbo has already compressed that air (using power from the exhaust). And if it leaks off, that's not only wasted potential power, but also wasted energy from the turbo.
-Check for exhaust leaks. Not only between the turbo and the manifolds, but also between the manifolds and the block. Exhaust leaks reduce the amount of energy available to turn the turbo.

Don't know if this is related but lately I have been experiencing hard starts in the morning. Had to crank on it 4 different times this morning before it would fire up.
I don't know if it's related either.

Have also noticed on a couple occasions that immediately after start up when I first go to pull away, the truck has absolutely no power and will hardly accelerate. After I get rolling about 75 yards it comes to life.
2 things I've noticed on my truck:
-Glow plugs pull down the battery voltage, which reduces the power the IDM can output to the injectors. This does make a noticeable reduction in power.
-EOT sensor. If it's on it's way out, it may read the oil temp is higher than it actually is, causing the PCM to command slightly retarded timing, making the truck slugish until the engine either warms up, or get to higher RPMs where the timing comes back closer to where it should be for the actual oil temp.
 

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Twitch
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I can only get about 15 mpg on the highway. I realise all above what you said but even so it should get better than what I'm getting and 10 mpg towing 5K sucks for a diesel.

As for hard starts...I replaced the GPR yesterday so will see if that helps.
Hate to say it but 15 mpg maybe the best you will get out of it if these other little things check out. Some times the brake pads have been known to stick on the rotor when not being applied thus dragging your fuel mileage down even more...just a thought.
 

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Discussion Starter · #8 ·
All I ever run for oil is Rotella and change it every 5K. Doesn't seem to make a difference if it's fresh oil change or not.

Brake pads are good. Have had wheels off numerous times for various reasons.

As for boost and wasted power...I was out today driving and was watching my boost gauge while running around. I was in 80 daily driver tune. I am getting about 5 pounds of boost with what I will call moderate acceleration at around 2000 to 2200 rpm. Is this normal? Seems a little low to me but I'm no expert. I was suspecting maybe a leak in the up-pipes but I can reach around 24 pounds of boost at wide open throttle so I wouldn't think that would be the case.
 

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15 mpg with those tires isnt bad......
 

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I get 12 mpg on my 7.3 and have the same size lift/tires as you. Its a 7.3, your gonna get chitty fuel mileage
 

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What else?
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I get 12 mpg on my 7.3 and have the same size lift/tires as you. Its a 7.3, your gonna get chitty fuel mileage
I wouldn't agree with that, because both mine have gotten plenty better than that. My 4.10 truck gets about 17 on the highway at 72ish, and my 3.55 geared 97 I had would get just a tick over 20 at 72ish. DD'ing around here they were 15/17, respectively.

OP, you have an 8k lifted truck with 35's, with 3.73's to boot. It's not going to get the mileage most other 7.3's get. Sometimes it's the loose nut behind the wheel that needs adjusted too. ;) It sure helped my fuel mileage.

I would also suggest checking the little things, like the caliper guide pins, they are notorious for seizing. You can't check them just by taking the wheels off, you have to actually take the calipers off and pull the pins out.

Dave
 

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Discussion Starter · #12 ·
smokeyred I agree with you. I know this truck pretty well and it is capable of more than what it's doing. I've had the calipers off...just replaced the front axle u-joints.

With that said, I checked my up-pipes last night and they are showing some soot where they connect to the y-pipe so I am for sure loosing some boost. Now I need to figure out if I wanna do a quick/cheaper fix and replace the gaskets or go with new International up-pipes. Suggestions...
 
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