Engine/Transmission (1994 - 1998) 12v AFC Mods walk through

[JKosten]

After a lot of researching of how to modify and tune the AFC on my P7100, I have collected the following guide:

The following modifications to the AFC may not be either emissions control approved or safe for the motor if done incorrectly! Adjust with caution and precision as anything falling into the pump will result in a very long night.

A quick introduction to the Air Fuel Control (AFC): The AFC's purpose is to meter fuel in a relationship to the amount of air (boost) the engine is receiving. The main parts of the AFC can be seen in the following photo:

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How the governor fits in:
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The AFC arm rides next the the fuel WOT stop or "fuel plate" and limits fueling when the truck is not under boost. This allows for the engine to build lots of power while under boost but still run somewhat clean and defueled while coasting.

This may not be what some people want if their goal is to smoke, but for the most efficient tune while still getting power the following can be done. For more smoke (AKA unburned and wasted fuel) when bench setting the AFC make it go full fuel at 15psi or less.

First thing to do is to remove the afc from the injection pump. (this is not my AFC, it is at the end... )
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Next remove 4 screws (1 is a break off screw) to get to the AFC diaphragm.
You will need to replace the break off with a normal bolt (metric).
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AFC diaphragm.
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Next remove 10mm (socket) nut holding diaphragm on. The AFC arm prevents it from rotating.
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"Once the diaphragm is off remove the cupped washer on the spring side and replace it with a flat automotive body washer with the same outside diameter and 8mm hole. " I chose to flip the two oem washers and grind the cup down to get the clearance from the housing.
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Now that part is done, put diaphragm back in and cover back on.
Next modifying the AFC foot.
Remove 10mm bolt holding the slide shaft in. (I did this when putting my rack plug in not knowing about the cup washer in diaphram)
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Take a flathead screwdriver and pry out slide shaft.
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Continued on next post due to pic limit!!!

 

[JKosten]

Remove shaft and afc foot.
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Now grind 1/16" to 1/8" off the round part of AFC foot that slides on the shaft.
Make sure to not leave any burrs that could wear the shaft it rides on.
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Now that part is done reassemble AFC foot and shaft.
That's it for the rack travel mods.

Next is the smoke screw (AKA non-boost base fueling). The smoke screw is located behind a small cover on the diaphragm cover. Remove 2 screws (one break off) pull off cover.
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This controls the 0 boost fueling, the further in the screw the more tension it puts on the afc spring, allowing more fuel to come on with no boost.
Smoke screw on inside of cover.
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To adjust smoke screw loosen lock nut 10mm, use 3mm allen wrench to adjust smoke screw in or out.
Smoke screw all the way out.
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This adjustment can be done at any time, on or off the injection pump.

Last is the star-wheel.
Remove plug located on top of AFC using 8mm allen wrench.
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The best way to adjust the star-wheel for proper fueling is to use regulated air. Use an air blow gun with a rubber tip or a 1/8 compression line to a air fitting, set pressure on compressor regulator to the psi you want full fuel.
I set my fuel fueling at 30ish psi as my waste gate is around 34psi. This will give full fueling at full boost.
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0 psi
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20 psi (at factory wastegate setting and fueling)
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30 psi full travel
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Install star_wheel plug back on AFC.

Now that the AFC is complete install on injection pump, adjust AFC housing forward or back according to you're tastes. The smoke screw can also be adjusted at this time too. Just remember to put the small cover back over the smoke screw when the fueling is to your liking.

The main portion of this walk through can be found here: AFC Mods from KBBT - DieselRam.com