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?

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.

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?

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.

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?

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

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

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

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?

when you grind the barrel are we grinding the front of the barrel( towards the front of the pump?):humm:

I bet he just loosene the starwheel so it would smoke on the low end. tighten it up a bit silde your housing all the way back and see how it feels. If you don't like it you can always put it right back where you had it.

Yes about .090 ... I'll get a pic up later

Look at the 2 stickies on top of the section; one is called tuning the afc or something like that. There is a picture and it shows exactly which portion to grind

it does haze a bit putting around, and it smokes like a banshee until the turbo boosts when I floor it or if I lug it. So tighten the starwheel up towards the firewall?

Oh also I just remembered somethign; the guy that did my afc said he has it set to take off like a bat out of hell at 1700rpms. He asked what rpm I want it to really kick in at, and he said 1700 is a good rpm because that puts me abotu where the turbo starts boosting. Soooo whatever that means he did, you guys might know what he means.

with all that fuel on a stock turbo you should be boostin up before 1700?

yes tighten up the star wheel for now till you get that stiffer spring in it. twords the cab. your stock charger should light before 1700 rpms, your def putting the fire out.

Nope its a SLUG until about 1700rpms, then at 1700rpms it takes like a bat outta hell man.

But something interesting I JUST noticed. My bottom 2 afc screws are awol:s::argh: How the hell did those come out?? I notice smoke and oil and stuff blowing out, and when the motor is reved the whole afc moves lol. Sooo could that be the culprit for poor mileage too or no?

yeah it could

do you mean it smokes like crazy and goes no where?

Ok long story. To answer your question, what I ORIGINALLY meant was when I was reving it under the hood it was smoking from the region of the afc.

But NOW my fucking turbo is fried AGAIN! I just replaced it a few days ago! Coming home from work I noticed it wasn't boosting anymore, gutless and rolling black smoke. Figured the afc was playing games.

I fixed the afc, now I test drove and same results. I'm soooo pissed I could torch this stupid piece of shit. Last time I test drove it I floored in first. No boost only sputtering about 2100+. Slammed the brakes and think I saw white smoke rolling past me. Turbo still spools (I can hear it) just doesn't boost.

I'm so fed up with this fucking thing. I bought it was a project (read: MODS, front cover fix, paint etc).. and this thing is only projecting my fucking bank account into the black

wooooh clam down there bud its prob a simple fix, if you can hear the turbo spooling its prob a boost leak some where.

No I dont think its a boost leak. It came on the same way my last one blew a few days ago. Was cruising, all of a sudden right before I shifted (around 2k) it started sputtering, throwing smoke and being gutless. Only this time I dont hear the impeller clanging around. But i"m pretty sure its busted. There isn't anything thats been done that would cause a boost leak.

Is there any shaft play or are the blades messed up any?

Dont know I was too pissed to look. I'll probably take a look tomorrow since i'll have nothing else going on. I'm literally sick to my stomach with that truck I cant believe how its one thing after another.

I know exactly how ya feel. Been through the same thing with mine, so pissed at it I had it for sale for a few months actually but I knew I would miss it if I would have sold it.

Well sure as hell I went upstairs to my wife and told her its for sale. I'm tired of being let down with this damn thing. I wouldn't be half mad if the mileage was good when it was running, but since I got it tuned and did all the work to it I'm getting 4mpg LESS on the highway than stock w/ a 3yo fuel filter! So what exactly could it be then? I'll check for shaftplay and the impeller tomorrow. But what else? Doesn't appear to be any boost leaks.

You can't "look" for a boost leak... You have to pressurize the system and inspect all the connections around the boots... You should try to post in one thread insted of multiple ones that are on different things that all turn into the same thing.

I'm saying there are no obvious boost leaks thru couplings or anything. But I dont foresee any boost leaks magically popping out of nowhere that would cause a zero-boost situation

if the turbo sounds like its spooling and theres grinding noise, then the turbo seems to be ok. make sure on the bottom boots by the intercooler they didnt blow a hole in the bottoms. or something. if the turbo sounds fine, it should be fine. you obviously not getting the air into the manifold, and it wouldnt hurt getting new upgraded boots and clamps anyway.

Ya no noises yet. I'm checking the imp shaft and blades tomorrow. Also gonna check the flanges for proper fit and secure and dtuff like that. Gonna check stuff and report back to u guys. I'm sooo pissed tho this second turbo better not be fried.

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The impeller shaft still spins. Checked for obvious boost leaks again, nothing happened. Truck doesnt smoke TERRIBLY like it did the first time I friend my turbo; I can drive down the road and not smoke too bad. But as soon as I hit 1800+rpms it starts sputtering and popping like crazy. All the flanges are tight. Afc is looking good. I have a line going from the intake manifold to the afc, so the line from the afc to the wg is staying capped.

Somethign I noticed when driving it today. The turbo is NOT as loud as it was, and when I let off the gas the air doesn't "woosh" back into the intake.

Another thing I thought of was even when the truck was working right, the first cold-start of the day if I gave it too much throttle around 1800rpms or so it would pop and sputter real bad until its driven for a few miles. Dunno if its relevant or not.

when mine is cold it will kinda pop and sputter if i rev it up to, did you check for a pre trubo exaust leak?

yep checked there everthing was good to go. Only place thats obviously leaking is the vband right before the downpipe.. but thats after the turbo so it doesn't matter

sure your timing didnt slip?

No i'm not sure but even if it DID slip, why would my turbo not whine half as loud, not "blow off" on shifting, and the truck wont go much over 1800rpms w/out sputtering real bad

That all could be low timing related, along with your bad MPG, and super easy starting.

Its funny you mentioned the super easy starting thing. Since putting in the starter and doing my mods, new fuel filter, and everythign in my sig it actually starts normal now. When it was in the 20's the other day the truck def took a second to start and I had to rest my foot on the throttle for it to start.