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5.9L 12V Performance Discussion of 12 Valve 5.9 Liter Dodge Cummins Diesels with P7100 Injection Pumps Related to Performance and Longevity

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  #1  
Old 04-11-2010, 05:29 PM
Being Evaluated

   

Default How to tune afc for mileage AND power?

If you guys have seen some of my other posts, when my truck was bone stock, had a 3 year old fuel filter and gunked up air filter, stock exhaust, stock fp etc.. I was getting 19.33mpg highway going 80-85mph. NOW, with my bhaf, straight pipe, fuel plate, afc 3/4 forward, and fp 3/4 forward, I am getting SIXTEEN MILES PER GALLON going a VERY consistant 68-71mph!!! My buddy that helped with the fuelplate tuned the afc and starwheel; did he do something that gave it terrible mileage? I mean, this thing is FAST; w/ 1k lbs of sand bags in the rear I can get the dually sideways in 3rd gear on accident sometimes, yet when I baby it to gain max mileage I get 16mpg?? I'm pissed. I cannot put into words how pissed i am getting 16mpg highway, going only 68-71mph. Thats insane. Most people get that mileage when TOWING on the highway.

So my question is, can the afc be tuned for power AND efficiency?



EDIT: For everybodies info, before this trip I swapped my busted turbo for a 2001 hx35 w/ boost elbow gated to 33psi, silencer delete, etc. I capped off the afc line with a screw and clamped it. Could anything in between there have caused poor mileage?

Last edited by 85_305; 04-11-2010 at 05:33 PM..
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  #2  
Old 04-11-2010, 05:46 PM
94 12valve's Avatar
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Status: " it only makes 500 hp hes not gonna do well"

   
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slid your afc all the way back, put a stiffer spring in it, and mod the barrel for full travel.

While you have the afc off the truck hook it up to a air source to test what press it goes FF at. I have had the best results with going FF at 30psi.

94 12valve's Sig:Dave

2.6" Puller
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  #3  
Old 04-11-2010, 05:51 PM
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So will I gain or lose a lot of power going afc all the way back? What kind of mileage will I pick up? Should I move my fuelplate all the way forward when moving the afc back?
Where can I buy that spring from? Links?
How do I mod the barrel for full travel?

So you are saying my truck will perform better power AND mileage wise, with the afc all the way to the rear w/ a stiffer spring and properly adjusted barrel?

Last edited by 85_305; 04-11-2010 at 05:55 PM..
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Old 04-11-2010, 05:57 PM
94 12valve's Avatar
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Status: " it only makes 500 hp hes not gonna do well"

   
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you should not lose any power

I don't know how much you will pick up but it will help. If you have the old gov springs from your gov spring swap just use it, works very well.

grind .090 off the barrel and swap the washers.

And yes that is what I am saying. you will have less bottom end smoke with the same fueling up top. I lost 60 rwhp on the dyno when I had my afc set to loose, I " Put out the fire" as its called on the low end.
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  #5  
Old 04-11-2010, 06:06 PM
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Ok good deal man. I dont have the gov springs yet though so where can i pick a better afc spring up from? You mean swap the washers w/ regular Lowes washers right? I remember reading about that.
What do you mean your afc set "too loose"? Too far forward?

I'll gain mileage by doing this for certain though?
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  #6  
Old 04-11-2010, 06:53 PM
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TST sells the kit comes with a heavy spring and a light spring. Yes about the washer swap. By too loose I ment I had way too much fuel on the bottom end.

You should gain mileage
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  #7  
Old 04-11-2010, 07:03 PM
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Awesome good to hear. Can I move the afc back before I actually buy the spring kit and chop the barell and swap washers? Will I still get better mileage and maintain the current power?

How much mileage you think I'll gain? I'm not getting anywhere near where a 5spd cummins should be
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  #8  
Old 04-11-2010, 07:07 PM
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yes you can move it back now and see what happens. Tighten up your starwheel when you have it back to see the advantage less bottom end
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  #9  
Old 04-11-2010, 07:10 PM
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My buddy who's a beast at 12v's messed w/ the starwheel; not quite sure what he did with it. Are you saying move it all the way forward (towards the cab)? Will I loose power moving the afc back right now?
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  #10  
Old 04-12-2010, 12:31 AM
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when you grind the barrel are we grinding the front of the barrel( towards the front of the pump?)

lodal cummins's Sig:1996 Dodge 12 Valve,100 Fuel Plate ff, Silencer Ring Removed, bhaf, AFC Tuned, Boost Elbow, 4"turbo backstage 2 75hp injectors
Boost & Pyro Meter Gauges, Automatic with low stall convertNer & Shift Kit
kdp killed,timing 15.5* 3kGSK Email: lodal@comcast.net
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