afc tuning explained

[OrangeP]

i figured i would make a new thread since the others get hijacked.

please anything i post that needs corrected please let me know.

im doing this as a favor for newbies and maybe alot of people still dont understand whats actually happening inside there.

keep in mind the afc housing as a whole is moveable as well, setting the afc full forward will allow most fueling, try to start with the afc full forward and keep it there everytime you take it off when making adjustments or moving plate, if you move the whole afc you move the afc foot as well.

*ok the yellow arrow in the back of the afc points to the smoke screw (pre boost)

*the yellow horizontal arrow on the smoke screw or pre boost screww physcally move the afc
foot forward and back,
this adjust instant fuel - this is what to adjust for spooling, touch the screw to the diaphram then
adjust 1/8 to 1/4 turn at a time to find best spool up

*the red circle is the starwheel, it adjust spring tension on how fast the
boost moves the afc foot, the tighter is is the more boot it will take to
move it full forward letting the gov arm touch the plate

*black circle is where the diaphram is along with the washer that holds
the spring to the diaphram, this is where you need to take the nut off
behind the rubber diaphram and replace the stock cup thick washer
with a flat fender washer

*the blue lines indicate full travel for the afc arm, these wont touch if
you dont remove the factory thick washer, some write ups say to grind
1/8 inch off of the blue surface on the actaul afc arm for extra travel.



maybe now people can see that is the afc arm is removed it lets the gov arm travel to the plate as soon as the throttle is pressed - dumping mass amount of fuel under not boost conditions.

if you have never had your afc off your truck, dont be scared, it comes off very easy and well as comes apart easy, you wont loose any small parts and it will only go back together one way. there is another really good write up onthe washer and trimming mod i cant find it right now, hopefully somebody will link it.

i just wanted to point out the parts and their function. made 100% more sense to me once i figured out what was actually moving and when.

[nolls96]

i think this should be moved to the tech section... unless anyone has anything they'd like to add or change..

i'd just like it to be known that the "smoke screw" and the "pre boost" screw are the same thing to avoid any confusion.. and also how fine of an adjustment it is, 1/4 or 1/8 turns to get close and even finer to find the sweet spot!! (i'll say that so algae doesn't have to)

[ykdave]

you also have the adjustment in the housing position also

And keep in mind that some adjustments will make an effect on the others.

For ex, tightening up the preboost screw to increase preboost fueling is also going to increase spring tension. If you were to slide the housing forward or back, you can alter preboost fueling without changing transient fueling characteristics (covered by the spring/diaphragm)

[Algae Eater]

Originally Posted by ykdave

you also have the adjustment in the housing position also

And keep in mind that some adjustments will make an effect on the others.

For ex, tightening up the preboost screw to increase preboost fueling is also going to increase spring tension. If you were to slide the housing forward or back, you can alter preboost fueling without changing transient fueling characteristics (covered by the spring/diaphragm)

Only thing to consider with sliding the AFC housing around is that unless it's all the way forward, it's not going to allow maximum fuel-rack travel.
And if you've modified your AFC [by swapping cupped washers for flat washers (5/16"ID fender washers) and grinding about .100" off of the AFC foot's surface that OrangeP put the BLUE LINE on... the blue line on the right above] then sliding the AFC housing back will lessen max travel.

[torqmonster]

Good post

[honestcharlie56]

Originally Posted by torqmonster

Good post

wow i wanna go to your house, its like a 12v museum..........

[ykdave]

Originally Posted by Algae Eater

Only thing to consider with sliding the AFC housing around is that unless it's all the way forward, it's not going to allow maximum fuel-rack travel.
And if you've modified your AFC [by swapping cupped washers for flat washers (5/16"ID fender washers) and grinding about .100" off of the AFC foot's surface that OrangeP put the BLUE LINE on... the blue line on the right above] then sliding the AFC housing back will lessen max travel.

Thats is why we do the AFC travel modifications

So that we can properly tune the AFC without effecting max rack travel!

Its like having your cake and eating it too!

[Algae Eater]

Sure. I know that, but...

I've never measured the maximum forward travel of the governor arm (with stock rack plug) versus the maximum forward AFC foot position to see how much clearance there is..

That would dictate how far back you could slide the AFC housing without there being interference that'd decrease fuel rack travel.

You could always grind more than .1" off of the AFC foot (some people do up to .2") which would allow you to slide back the housing without concern for rack travel.

--- edit ---

Actually that's not true. Grinding more than .1" off of the AFC foot is pointless, since even a swapped flat-washer in front of the diaphragm will be the limiting factor. That contacts before the AFC foot touches the front of the housing.

So even w/ grinding .1" off the AFC foot, there is still a gap in the front of it when the flatwasher/diaphragm have bottomed out on that back portion of the housing.

[goosekllr]

Good post thanks!

[12VEG]

Thanks for that OrangeP, moved it into the AFC section of the beginners thread, we needed something like that

Here ya go: http://www.dieselram.com/showthread.php?t=184064

Can a mod please move this to the tech section as well? Mods, are you out there invisibly?

Side note: Tech section could use a good cleaning these days...

[wjc9898]

I'm new to this 12V word, but this post has been a great help, along with many of the others I have been reading this weekend. I took off my AFC Sat. night and did the mods. One thing that I did that saved a trip to the store or rumaging around for the right washer, was to just take a minute on the grinder and remove the cupped portion of the original washer and use it that way. Now I'm just working on finding that elusive "sweet spot" I've been reading about. Thanks again.

[toms73novass]

Thanks for clarifying how all the parts work together in graphical format.