Drop in mileage.

littleredstroker · Aug 19, 2012

Bout a month ago took a 250 mile trip all interstate pulling a jet ski and a bed full of camping stuff, all interstate running 82 mph. This was the first trip since I.got the injectors . I made 19.2 mpg there and 19 back. Just made the trip again and this time no trailer empty truck and got 14.7... Running the same speed only thing different is new tires, they are the same size as my old ones.. any ideras

Sent from my HTC PH39100 using Tapatalk 2

Arisley · Aug 19, 2012

Fuel leak, head wind, boost leak. Look for the somple stuff first.

littleredstroker · Aug 19, 2012

Keepin about 10 psi which was the same as first along with egts bout the same. There was a little wind but now that you mention it I did catch a whiff of diesel about a week ago. I'll start there.

Sent from my HTC PH39100 using Tapatalk 2

Groomzybanshee · Aug 19, 2012

Hubs locked in?

littleredstroker · Aug 19, 2012

Hubs unlocked. Filter reminder is about halfway ... I suppose that could be part of it

Sent from my HTC PH39100 using Tapatalk 2

Groomzybanshee · Aug 19, 2012

Same tune?

littleredstroker · Aug 19, 2012

Yep. Economy

Sent from my HTC PH39100 using Tapatalk 2

TARM · Aug 23, 2012

How did you compute your mileage when you got the 19.2 this first trip? For that speed with something in tow no matter how light that is quite a high mpg for any 7.3
I suspect something with that mpg. The 14.2 does seem a bit low but if you are heavy on the throttle during take offs and it does not take much just spirited take offs or acceleration I could see this being close. Add in new tire which always pulls down MPG from the increased traction/friction compared to a worn down tire.

Your first mileage (19.2) is what most 7.3 even stock ones would get if they were holding 65 unloaded in reasonably flat areas.

If you have auto hubs and you had locked the hubs at any point between the two times you should physically check the front axles to make sure they are really unlocked.

Groomzybanshee · Aug 23, 2012

TARM said:
How did you compute your mileage when you got the 19.2 this first trip? For that speed with something in tow no matter how light that is quite a high mpg for any 7.3
I suspect something with that mpg. The 14.2 does seem a bit low but if you are heavy on the throttle during take offs and it does not take much just spirited take offs or acceleration I could see this being close. Add in new tire which always pulls down MPG from the increased traction/friction compared to a worn down tire.

Your first mileage (19.2) is what most 7.3 even stock ones would get if they were holding 65 unloaded in reasonably flat areas.

If you have auto hubs and you had locked the hubs at any point between the two times you should physically check the front axles to make sure they are really unlocked.

My truck with the hybrids gets better mileage than my stock splits ever thought about.

TARM · Aug 23, 2012

That I believe as I have seen it with my setup as well. With that said there was likely a turbo change as well as I also had not to mention how many miles were on those stock injectors or did you own the truck when it was low mileage? I do agree that it seems at the very least single shot gets better mileage than the splits and the lower the drive pressure at cruising the better the mpg as well.

Would you agree though that 19.2 mpg @ over 80 mph with a trailer and full bed is not in the normal range regardless? With 3.73 that puts him around 2500 rpms not exactly good mpg territory unloaded let alone adding in the weight and wind etc from trailer etc...

Groomzybanshee · Aug 23, 2012

Yea 19.2 pulling a trailer? Must have been down hill with a tail wind.

Strokersace · Aug 23, 2012

Groomzybanshee said:
Yea 19.2 pulling a trailer? Must have been down hill with a tail wind.

In neutral. Being pushed by a Kenworth.

littleredstroker · Aug 23, 2012

Ha ha ha.. funny. It puts me 2150 rpm, I.filled up on a flat surface both times untill the neck is.full and will not take any more, even.after a couple shakes. With my stock injectors I would get 18-19 empty on the interstate the jet ski and trailer maybe weighed 800 pounds total.

Sent from my HTC PH39100 using Tapatalk 2

littleredstroker · Aug 23, 2012

I have made it from bizmark nodak to casper Wyoming ( 525 miles) filling in biz and having fuel light come on as I am.coming into town. 29 gal tank...you do the math.

Sent from my HTC PH39100 using Tapatalk 2

Groomzybanshee · Aug 23, 2012

Lol no you do the math... 525~29=18.1 not 19.

TARM · Aug 24, 2012

We won't also include the fact that the low fuel light can swing wildly based on how much fuel is actually left when it trips.

What follows in not directed toward anyone in particular just general info that is my opinion:

Look doing mpg testing is a bit more time consuming then just rough estimating factors that can make it quick and easy. Diesel fuel foams terribly when pumped thru a nozzle so you can never use when the pump cut off goes off or when foam meets the tank mouth. That can cause variations of 3-6 gals from my experience depending on tank size and configuration.

The way to do it somewhat accurately is to first fill up and take your time until you can actually see liquid diesel right to the tank tube's mouth or a point in the neck that can visibly seen. It can not be foam. You now have a rather consistent starting and reference point. This eliminates pump cut out variations etc. Also it needs to be on flat ground or you would need to fill up at the same station and pump in the same orientation at the end.

Now you simply drive until you have gotten enough miles to make it reasonable. Fill up the tank to that point again and compute the mpg from odometer and tank fill up difference. If you choose to rough guesstimate it and get mpg that are outside the generally accepted norms expect people to be skeptical as how can you even be sure.

That is the only way I know of to get consistently accurate mpg usage.

lincolnlocker · Aug 24, 2012

80mph and 19+ mpg with a trailer in tow, hmmmm i could def see the 14+ but 19 just seems a bit high.... unloaded with my truck other then tools and clothes, full of fuel and the rear drag tank full that holds 90 gallon and all weighs in at just shy of 10k, i managed to get consistent 14.5 mpg from Michigan to frisco bay in cali running 80mpg with the cruise set...

littleredstroker · Aug 24, 2012

Groomzybanshee said:
Lol no you do the math... 525~29=18.1 not 19.

Like I said 18-19.

Ok so even with all the variables, if I do it the same exact way every time why would it drop 5 mpg.

Sent from my HTC PH39100 using Tapatalk 2

TARM · Aug 24, 2012

Because of those variables you seem to want to discount.

But if you would rather look for issue here is where I would start:

Brakes hanging Maybe a slider pin is stuck.

Boost or drive side leak

Tire pressure for those tires as each tire model can be diff.

Have you checked to see if you have any soft codes?

The thing is if you want to dismiss the variable but if each one just took a little bit and then you add in say 2mpg for the dif between new and used tires you are there.

Why not since it takes only just a little bit of extra time at the pump take the time to fillup as I posted then do your driving for a tank fill up again same way and see what your average is. I do this with every fill up and just record the data on my SG3 droid. I can then always check it back to see if things start to look bad or trend down.

Even if you can not do a all hwy trip one more tank will tell you alot. If mixed driving scores you the same or better mpg then your last 14.2 you can know it was a fluke or mis-cal on your part. If you are getting 14.2 hwy @ steady speed then mixed would likely be in the 11-12 range.

Honestly to loose the kind of mpg you think you have would take a fuel leak, something mech you would notice performance wise or a dragging brake again something I would think you would notice. I honestly think those variables likely stacked against you when you did the calculations between the two or you made a mistake some how.

littleredstroker · Aug 24, 2012

Possible. I'm not meaning to discount the variables , I just know I fill up till the nozzle shuts off. Then trickle it until fuel not foam comes out, give it a shake or two, then trickle it again. Same way every time. I have checked for fuel leaks, cannot find anything. Will test for boost leaks this weekend.

I do appreciate the info. I am also starting to second guess my fill up procedure. May have to take a short road trip tomorrow.

On another note I am not sure why 18-19 is so unreasonable . I aint no Cummings guy who is stretching the truth so my gf aint as pissed about the truck payment...

Sent from my HTC PH39100 using Tapatalk 2