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I’ve been trying to figure out my mpg issues for awhile now. Hand calculated on the last couple tanks I got about 13 mpg with mixed driving. The only time I get decent mileage is when it’s all highway running 70 in my hottest tune in which I see about 15 mpg (currently 1023 diesel Cummins killer tune but previously was 120hp race from php). I thought it might have just been winter fuel but it’s gone through several tanks during summer with the same results (this started last winter). I used to see up to 20 mpg on a highway trip easy without being easy on the throttle

So I was sure I had a boost leak/exhaust leak. I did end up finding my up pipes had a slight leak and I replaced them with full force up pipes, boots weren’t leaking but I went ahead and put on all new riff raff boots and new intercooler pipes, along with a wicked wheel, deleted the pedistal at the same time. Truck seems to make good power but the mpgs are still down. Reading up to 25psi boost on edge monitor.

Truck is an 03 7.3, stock suspension, 305/55r20 tires, edge cts2, hydra with 1023 tunes, wicked wheel 2, stock hpop, 5 inch exhaust, 6637 filter.

I‘ll note I did clean the ebp tube and sensor. put in a new motorcraft cps sensor in awhile back.

curious to know some others thoughts experiences. At this point I’m wondering if I should look towards hpop?

Thoughts and suggestions appreciated.
 

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I have the same mpg. 13-16 depending on how I drive and highway miles. If I use a tune, it can be less.

These guys who claim to be getting 16-19 must be driving like a granny or have poor math.

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Discussion Starter #3
I have the same mpg. 13-16 depending on how I drive and highway miles. If I use a tune, it can be less.

These guys who claim to be getting 16-19 must be driving like a granny or have poor math.

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Yes, I hear others say this is what they get and it is what it is but my only issue with that is that in the same truck I used to normally fill up with around 420-450 miles in a tank. Now I'm lucky if I see 375 or better. Note this is usually filling roughly 25 gallons.
 

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if you are this passionate about MPGs you should also consider drag.

I would baseline air pressures, tread life, grease all the drive line points, check the carrier, and ensure you have fee brake calipers.
 

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What is your fuel pressure? Reason I ask is you say you get the best mpgs on the highest tuning....which would be more HPO pressure...which maybe makes up for a lack of fuel pressure?

Thinking aloud here.
 

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These guys who claim to be getting 16-19 must be driving like a granny or have poor math.
Both my trucks can tag 20 mpg on the highway going 65mph.....the 97 has 3.55 gears and the 99 has 3.73 gears...I'd bet the consistently lower mpg trucks have shorter gearing (4.10)
 

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Are you adjusting your mileage based on your tire size? 30/55/20s are like a 33" tire. Factory was 30 or 31 i believe. That will make you show a lower MPG. If your odometer shows you drove 375 miles, you probably actually drove 415-430 miles
 

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I got close to 20 when I bought my truck 11 years ago. I cant break 15 now. The switch from low sulfur to ultra low sulfur really hurt my mpg. At the end of the day these trucks are bricks. They will only do so much. The fuel pressure idea is interesting. I have replaced damn near everything over the years on mine. And just cant get any better anymore. Might be something to check.

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my truck has its own set of problems (just started a new thread: it’s a pretty big fustercluck so take these numbers with a pinch of salt). but in city I’m getting 12-14.5, 10-11 towing a 3k boat through Tampa at 45 avg, and highway speed avg 65-70 across the state I’m getting 17-18 depending how hot it is, (south Florida rarely gets below 60) trucks sitting on 30’s
 
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