Horrible fuel milage????

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dodgediesel4x4

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Feb 15, 2010
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Ok, here's the deal. I have been getting terrible milage for the past few months and I can't figure out why. When I first did the swap, i was getting 14.5 to 15 mpg. I drove the truck like that for a few weeks and then swapped out the springs to the 4k. Since then, I have gotten horrible milage, anywhere from 7.5 to at best 12mpg. I have found a few boost leaks here and there and fixed them. I had the afc and grouond down plate full forward, then tried housing all the way back and plate half way. Still no luck. I tow atleast a few times a week (10-15k) and it doesn't seem to affect my milage (still crappy). Most of my miles are highway and I'm getting sick of this milage. The truck runs great and sounds great too. I haven't tried adjusting the springs because of that. Need some ideas guys...
 
What kind/size of injectors are you running, and whats your timing? Gov. springs won't affect mileage unless your driving style changes.
 
I've got mach 1.5's and my timing is 18.5. I've been driving with a very light foot. I'm having my diesel shop double check the timing this week just incase...
 
How many miles on the injectors? Maybe they need to be freshened up? My truck gets sh!tty mileage as well, but I assume its from my noisy, unknown mileage/brand jammer twos....
 
My injectors have probably close to 100k on them. You might be right on them needing to be freshened up... I havent had my timing double checked yet, but I did find a couple of very small boost leaks, haven't had a chance to check on my milage yet (been towing heavy alot).
 
Smoke seems normal. It is pretty consistant and doesn't seem to black out an intersection unless I get on it pretty hard. I had a buddy follow me the other day and he said it blows a constant "haze" just while cruising down the road (no WOT). For some reason I see the smoke being somewhat lighter in color than I remember (its not a super dark black color anymore), just a medium black to light black at wot or firm take off.
 
definately wouldnt hurt to double check the timing. sounds like it may have slipped

im averaging upper teens with my truck around town and can get into the 20's on the highway driving it nice. im running 110hp injectors, 024 dv's, 100 plate full forward,no afc foot, and a 4000gsk and it dosent haze cruising down the road
 
im averaging upper teens with my truck around town and can get into the 20's on the highway driving it nice. im running 110hp injectors, 024 dv's, 100 plate full forward,no afc foot, and a 4000gsk and it dosent haze cruising down the road[/QUOTE]



well that makes me feel better as ive about got all the stuff together to do a p-pumped 24v and going to drop in a reg cab short bed but the milage was worring me.
 
hunter I've got 3x the fuel you do and I don't have a haze going down the highway. Read up on afc tuning.
 
all the AFC tuning in the world isn't going to solve a haze at cruise, that's either slipped timing or possibly an issue with one of the injectors.

if it was me, I'd re-check the timing, and if it's good then I'd pull the injectors and have them checked and go from there.
 
Its my understanding the the aneroid fuel control limits low end fueling?? Why would that not help a slight haze? Mine had a haze when i first put pump on and since changing the spring and tightening up the star wheel it doesnt do it anymore.
 
I got 17.8 my last tank. Hoping to be around 18.5 this tank. Plate is 3/4 forward and afc housing is 1/2 forward.
 
Back off your pre-boost screw 2 turns and see if the haze goes away. I have a zero plate full forward, modified afc full forward, injectors that flow 45 percent more than a 240hp injector(Mach 7), a 750cc 13mm pump(rated with HFDV's, but running smaller 024dv's so the output is less), and a pair of laggy turbo's. I get just under 18 combined city/ highway, and 19 with mach 7's. No idle haze, no haze at highway speed.
 
Thanks guys. Im gonna try fine tuning the afc here in the next few weeks and go from there. I won't have time to do it anytime soon or re-check the timing, so I'll keep yall posted when I actually get to wrenching on it.
 
dodgediesel59 said:
Its my understanding the the aneroid fuel control limits low end fueling?? Why would that not help a slight haze? Mine had a haze when i first put pump on and since changing the spring and tightening up the star wheel it doesnt do it anymore.
Click to expand...

it does control low boost fueling, but you aren't touching the afc unless your foot is in it accelerating, at cruise you aren't going to effect your fueling with the pre-boost screw or starwheel unless you tighten the starwheel and reduce pre-boost fuel to the point that you are reducing fueling at cruise, at that point you aren't going to have enough fuel to maintain speed.

one other thing that could affect this, what turbo are you running?
 
[QUOTE

one other thing that could affect this, what turbo are you running?[/QUOTE]

Im running an older Super B. I know it has "some" play in the shaft, but I can't see the turbo being the cause of worse fuel milage in such a short amount of time. Still haven't had time to fine tune the afc.....
 
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