As I have been reading threads for the past several months, I have been trying to understand fuel plate positioning. I haven't found any thread that just spells it completely out. The following is my guess as to what happens if you move it fore or aft. Please correct me if I am wrong:
As you position the plate further forward (toward the front of the engine) you will make the engine run richer. More smoke, less fuel mileage, lower EGTs. More or less power is probably dependent on a lot of other things.
As you position the fuel plate further back (towards the rear of the engine) you make the engine run leaner. Generally expect less smoke (if it smokes), better fuel mileage, higher EGTs.
Does moving the fuel plate only affect full throttle situations?
Am I remotely close on any of this? Mine is in the neutral position, but have been reluctant to change it because of my lack of faith in my understanding of what I am doing. Any enlightenment on the effects of moving it would be appreciated.

 

I think plate positioning affects the amount of fuel in relation to the govenor arm.Assuming that you havnt gutted it.Some guys completely gut the afc and then your foot does all the fueling parameters ,no more relation to boost signals.In regards to moving it a bit,I would slide it forward all the way and see how it drives ,then you can fine tune it from there.You can also slide the afc housing forwards as well if you didnt know that already.As far as the technicalities of it got,Im by no means experienced with 12v's ,some others will lend their advice Im sure

 

Think of the plate as a brick under your pedal. The farther the plate is to the back, the thicker the brick, less pedal you have. Push the plate forward, the brick becomes thinner, you can push the pedal down farther. If you removed the AFC foot, you can actually feel in the pedal when you hit the plate. If you push harder on the throttle, springs inside allow the pedal to travel, but the governor arm, and thus the rack, do not change, so you won't get anymore fuel.

http://www.cumminsdatabase.com/read.php?id=182
This is a handy cutaway of the pump.

http://www.cumminsdatabase.com/image...100_diag02.jpg
Here is a diagram of how the pluger/barrel assemblies work. The rack turns these plungers in the barrel, and due to the helix cut, it will vary the amount of fuel that is delivered.

 

move it forward for more power (smoke might join), higher EGT's (depends on ur pump, 180 and 215 pumps prolly get hotter than the smaller pumps), MPG might suffer alittle but u can generally tune the afc to not affect mpgs. I have my plate full forward, u have gauges so put it forward also and see how u like it. U might want to check ur Gov arm, (Piers diesel website has the how to on that) to make sure it hits the plate in the right spot for maximum efficiency. And i can almost bet u'll want more power after u get use to that, so injectors and a turbo come next :-)

 

We put in a pretty mild plate, and got a lot of EGT rise even so. The four-inch turbo-back exhaust brought things down to reasonable again.

I heartily second the governor arm adjustment - it was a BOOGER to actually do (working blind, using a little mirror to see into the AFC housing) but WELL worth the pain as it really smoothed out the feel of the throttle and response all through the range.

The 3000 rpm Governor Spring Kit made a huge difference in throttle response as well - and having done it with the kit from TST, I'd not want to take the cheaper way of guessing on washers etc. That's another job I only want to do once. But then, I'm old and creaky and hanging over a 4x5 truck fender all day is real hard on my back

 

In a nutshell:
Forward is more fuel, more smoke, higher EGT's, stronger bottom and top end.
Back is less fuel, less smoke, lower EGT, less bottom and top end.

Mileage can be fine tuned with the AFC so it really isn't affected under normal driving conditions, unless you drive with the pedal wooded at al times.

 

Thanks for the synopsis, Mike
I am very happy with my truck's power right now. It actually runs just great. It pulls my trailer right up any normal hill without hardly grunting. That's with 8,000 lb total truck weight (with my bike and all the gear in the bed) plus towing a 7,000 lb trailer.
My EGT's get a little high (I am assuming), around 1350 to 1400 on long hard hills while towing. (I end up downshifting and sometimes backing off the gas for EGT concerns alone, not because I am out of power) I assume I should keep the EGT at or below 1200 F. My milage is around 16-18 empty and 10 to 12 mpg loaded. (I would expect a bit better. I drive relatively conservatively. I tow at 65 mph and drive empty at 70 mph, and dont bury my foot in it that often).
I assume that I should try moving my fuel plate to the back some, then.
My next question would be how do you tune the AFC.

 

Anyone who has bought an aftermarket plate may have read to install it in the stock position.
Reason for this is because then you don't have to adjust the gov arm.
Sliding the plate fore and aft can duplicate the plate numbers on either side of the installed plate.

 

hi
what do you mean by duplicate the plate numbers ?

 

By sliding a #10 you can make it behave like a #8 or #11

 

I am not the author of this, I copied and pasted it from another forum. Just a little information here, it may answer a few of your questions. Like all information, you have to pick out what will work for you and question the rest. A good start though.

Let's start with gov arm adjustment. Now maybe I'm just reading too much into it but I set my gov/plate contact with the engine running at idle with the AFC cover off. Why? I got to studying the stock plate and with the engine off, the common knowledge is to set the lever where all the cutaway images show....BELOW the big protrusion on the plate. Then I got to wondering about how that arm is smoothly going to ridse over that protrusion. So I looked at my 100 plate conmtact with the arm at rest (solenoid in run position tho) then fired up the engine and checked it again. The lever won't swing out until you lightly stab the throttle, but I noticed that the arm contacts the plate a lot higher than at rest. We can only attribute this to gov springs acting on the gov arm. So rather than set the plate with the engine off, I run it and set the plate to the arm with the enginre running. The difference in arm height is about 1/4 inch...coincidentally about how much higher the arm would have to be to clear that protrusion on the stock plate. So my belief is that when running, the arm starts on the protrusion and not below it as it would seem. Now not many of us are running stock plates, but the theory applies anyway. I have never had to adjust my gov arm to a plate.....except maybe the "0" I was running for a while. Now I'm not passing this along as gospel, or to shake the foundations everyone swears by, but if you car to dabble, have a go at it and see what I mean. While my engine is off, my arm will swing under the plate, but have never had it bind underneath...this is proof to me that my theory is correct. So if you're setting the bleeding edge, maybe setting the arm on the nose of that pointed plate would be better done while the engine is running.....and hopefully you can get the plate where you want it without adjusting the arm any!!

Next for the AFC.....several adjustments there, but not everyone understands them completely. At this point we know that the AFC is there to limit fuel supply during low, or no boost conditions. That's itsa only function, cut and dried, don't let anyone tell you differently. With a stock spring, after about 6 psi, no more AFC influence on the pump...that simple. If you have low tension springs in it, cut that down to about 2 psi. We know that the AFC lever protrudes down into the pump cavity right next to the fuel plate, and at no or low boost, it catches the gov arm and limits fuel that way. So what are we doing by moving the housing forward? We are simply moving THE ENTIRE ASSEMBLY farther to the front of the engine which allows the gov arm to travel farther which allows more fuel....that simple. So what about the star wheel? That wheel acts on a spring that pre-loads the pressure diaphram which is boost controlled. If we turn the starwheel towards the engine, it moves forward, releasing spring pre-load on the diaphram. As this pre-load goes away, it takes less boost to act on the diaphram and move the AFC lever out of the gov arm travel path. We think of these as the fine and coarse adjustments for the AFC, which is not totally true. The coarse adjustment is indeed moving the housing itself. But the fine adjustment is not the starwheel.....it's the so called smoke screw. You don't see this becasue it is on the back of the AFC housing under a sealed cover with a break off crew. This screw actually bottoms out on the diaphram center...from the boost side of the diaphram. And what happens when we add boost? The diaphram moves the AFC lever out of the way right? So by screwing this stud in, we give the lever a head start getting out of the way...much like moving the housing. That is why it is truly the fine adjustment. So we can set the housing in one position, then fine tune that position with the smoke screw. These adjustments alone will influence off idle smoke....not the star wheel. The star wheel will influence how long it takes to come off pre-boost fuel and into full fuel. So lets tune a pump...

We buy a truck and the previous owner moved the housing forward, cranked the starwheel fwd and didn't even know about the smoke screw...so it's in it's stock position. The thing smokes off the line like a freight train and bogs like crazy...then when 6 or 8 psi comes around, it surges with power and breaks all the tires loose....that darn turbo lag right? Now let's tune the afc.

Start by getting the access to the smoke screw...take the AFC off and remove the break off screw and smoke screw cover. Loosen the smoke screw lock nut and back out the screw several turns until it feels loose. Now screw it back in by hand until you can "JUST FEEL" the screw bottom out on the diaphram. Snug up the lock-nut a little and now set the AFC back to a middle position on the pump. Take out that hex plug on top of the AFC and bring the star wheel back from full forward about 3 full revolutions and put the plug back in. Now we have a starting point. Put her in gear and nail it. Do we have any smoke? No? then adjust that smoke screw a little at a time until it "just hazes" on take off. If you can't get that, loosen the smoke screw about halfway back out and reset the housing .020 farther fwd or so. Now try it again. Still no haze....adjust that screw in to get it. Or did we have too much smoke? back the screw off until it clears a little. You get the idea right? Any more than a slight haze off idle and you're wasting fuel, and maybe even hindering spool-up by quenching the cylinders with excess fuel and "puting the fire out" so to speak. So let's say we got the off idle launch looking good. Now it launches good but it takes too long for the turbo to come to life and the smoke goes away but no boost and it's laggy. That means we need to lessen the diaphram preload with the starwheel. This will hasten the curve out of pre-boost fuel control by allowing the diaphram to move with less boost pressure. Keep adjusting the wheel until there's a slight haze while you gauge shows less than 6 psi or so. If you get too much smoke once your RPM's start to climb, but before 6 psi or so, cranking the starwheel backwards will limit the fuel, cut the smoke, and smooth out the power. It's a balance game between the 3 adjustments....initial fuel delivery vs. building boost without quenching combustion. You'll know when you're right on....it'll launch hard, won't smoke, and boost climb will be smooth and rapid. These adjustments pertain mainly to the tune conscious driver, who wants drivability no matter who climbs behind the wheel, and isn't fueling for a funny car.

Now all of you have spotted my sig and said wait a minute...all this AFC tuning and he took his completley off...what gives? I DRIVE my truck, and my right foot does alot of the tuning as required at the timer of need!! You are not going to remove an AFC circuit and stomp the throttle from a stop and expect anything but a volcanic eruption with nothing to show for it!! You have to roll into the throttle as conditions demand, sometimes more, sometimes less. I like having that control, and not letting the pump decide for me with a one size fits all adjustment. I will tell you that boost response at speed is instant, and off-line punch is tremendous, once you learn how to drive it. Even at speed when our little boost gauges say 2-3 psi....guess who's holding the cards for you? Your AFC....still won't let you into full fuel until boost pressures are realized, and that just may be enough of a lag to give some half a car headstart during a rolling race.....excuse me....I meant to say when you need instant passing power. If you're a step on the loud pedal and go type of driver forget it...you won't like it. But...if you truly DRIVE your truck, give it a try....you just MIGHT like it.

To do this, you don't have to make a block off plate or remove the AFC housing entirely. You just need to remove the arm. This is easy....on the front of the AFC housing is a 10mm bolt that hold what looks like a bellcrank and shaft. Remove this bolt, then with a small screwdriver, pop the bellcrank loose and pull out the shaft. It will have o rings on it to seal the housing. Once this is out, lift out the AFC arm, put the shaft back in and snug up the retaining bolt again. Now it doesn't matter where the AFC housing is, or the smoke screw, or the starwheel....so just bolt it back on. re-attach your boost line....it'll still act oin the diaphram, but the diapohram won't be doing anything so don't worry about it. If you want to remove the AFC signal line go ahead...just remember to replace it with a plug in the manifold!! Now you right foot does all the adjusting for you on the fly, and is completely dynamic to conditions...cool huh? It only takes a few minutes to do, so if you don't like it, put her back in and forget about it.

Wow, this post is way long....sry guys. I have a habit of doing that. I hope I helped, but didn't confuse anyone.....

LAter,
Chris