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Discussion Starter #1 (Edited)
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.
 

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i think this should be moved to the tech section:thumbsup:... 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):lol4:
 

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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)
 

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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.
 

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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! :)
 

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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.
 

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

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...
 

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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.:truck:
 

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

:thumbsup:
 

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great post have a question thought you say adjusting you pre boost screw limits your afc travel for rack but what if you lath down where your star wheel.(on the face ) to give you the travel you want. or am i looking at the picture wrong thanks
 

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I know this is a late post, but I wanted to add some things to clarify just in case anyone is still confused.. :D

great post have a question thought you say adjusting you pre boost screw limits your afc travel for rack but what if you lath down where your star wheel.(on the face ) to give you the travel you want. or am i looking at the picture wrong thanks
You don't need to modify the starwheel to increase travel.

You just modify the AFC foot (blue lines in original photo AT START OF THREAD) by removing .1" from it's leading face. Then swap the cupped washer in front of the diaphragm with a 5/16" (8mm) ID x 1.5" OD flat fender washer.

After doing both of those mods, the limiting factor (which you will find if you disassemble and play with your AFC) is the new flat-washer, in front of the diaphragm (which the spring seats on) hitting the bore in the AFC housing as it comes forward under boost pressure. This is fine... it doesn't need any more travel than this to acheive full fuel rack travel.

If you slide your AFC housing all the way back, you may be limiting rack travel (especially if you have a 2095 rack plug and previously had the full 21mm possible rack travel) with these mods, but nobody has checked and verified this.

the preboost limits how for back it can travel.
This is true, but confuses people, because it says "limits" and "travel"... they seem to miss the fact you said "BACK"... if they think of it as a "limiting" adjustment, it just trips their brain up.

I think of it as a "pre-load" adjustment because it's at the resting position of the assembly. It pre-loads the start position to allow a precisely metered amount of initial fuel to light the turbo, which will in turn build enough boost to push the arm forward into the spring/starwheel's jurisdiction (aka "transient boost/fueling").. and this all happens in a split second if it's adjusted right... and somehow both the pre-boost & starwheel's adjustments are very crucial to acheive decent turbo spool.. if they're off, the turbo will always have noticeable lag and will spool 200-300RPM's too high..

You only hear of people whose stock turbos are spooling at 1800RPM because they (like most people) have never heard of the pre-boost adjustment.

An HX35 should be building boost pretty much off-idle... shouldn't lag at all.

--- edit ---

Also, I will add that (as previously said by others in this thread) the AFC Housing's position is very crucial to the pre-boost adjustment. If you slide the housing around forward & back, it totally changes the foot's start location in relation to what it's guiding (the governor arm) below, inside the pump's governor housing.

For that reason (and because I like full rack travel) I always slide my AFC housing fully forward when putting it on. That's where the pre-boost is set for and as long as it goes back right there, it's fine. But if 1/4 turn affects turbo spool, you can imagine that equates to less than a few thousandths of an inch in the AFC housing's forward~backward position. They're coarse and fine adjustments.. but the housing's position is VERY coarse when compared to the sensitivity of the adjustment and its impact on turbo spool, that's why you need to spend time adjusting the pre-boost screw or install a remote adjustment cable.


:D
 

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Man... I just grind the cup off the washer, grind the barrel, and adjust the pre-boost out as far it will go then slap that sucker on FF. Worked great with my old HX40 that had the 18cm housing and even better with this VGT set up. The only thing I had to monkey with was the starwheel and that didn't take long to dial in.
 

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could you clarify the governor arm follower rod and its importance , it is adjusted through the back of pump, the tech section made a big deal about it
 

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Man... I just grind the cup off the washer, grind the barrel, and adjust the pre-boost out as far it will go then slap that sucker on FF. Worked great with my old HX40 that had the 18cm housing and even better with this VGT set up. The only thing I had to monkey with was the starwheel and that didn't take long to dial in.
Most people need more pre-boost fueling to get the turbo lit.

If you ran my pre-boost all the way out til it's barely touching the diaphragm.... I would have 0 smoke off-idle and the accelerator would feel as hard as a rock (won't push in) until the turbo builds a couple PSI (which would take about 3-5 seconds) and then the truck will go.

Most people have never even tried messing with the pre-boost screw to see what it gets them.

But the more fuel you have, the less pre-boost you need. And how much you need depends on what turbo you're running too.

My buddy who was underfueling his silver 62 needed the pre-boost screw to be almost all the way IN! or it wouldn't build ANY boost.

could you clarify the governor arm follower rod and its importance
Could you clarify the question?
 

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could you clarify the governor arm follower rod and its importance , it is adjusted through the back of pump, the tech section made a big deal about it
The governor lever is what rides on the AFC foot, and fuel plate if applicable. It moves up and forwards while accelerating allowing the rack to move forward opening up fueling into the barrels, where the plungers push the fuel through the delivery valves. - If I understand it correctly -

Adjusting this gov. lever only needs to be done if the lever is diving under the fuel plate, which will either happen or not when you push the stock plate forward, or add a different one...

That sorta answer it?
 

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i am a visual learner and this helped AAAAA LLLLOOOOTTTT!!!!! just the cut away of the pump was enough but as me and my dad have 12 valves its great to know how to tune now.....kinda sucks his is a 4x4 and mines not but i got less mile and a new motor lol....any way great write up out of all ive seen this one is by far the most helpful
 
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