J_dude

Hey guys, so I'm trying to tune my afc to cut down on the freight train smoking issue all my gasser buddies think is so "cool", and yes I've searched and read about 3 dozen threads about it lol, but I've got a vehicle specific question that I can't find a good answer for. My truck is a '96 2500, 215 pump with #100 fuel plate, 4k gsk, 024 delivery valves, and some afc mods. Stock injectors as far as I know. Trying to figure out my starting point, like where the heck do I need to set my plate and housing to start with? Thanks guys!

J_dude

Forgot to mention, I've got an he351 turbo in there too and still a TON of smoke till she spools, then it takes off and boost gauge jumps to 40 in a heartbeat (I love this turbo lol). I've got a pretty good handle on how to tune the afc from all the reading I've done but trying to figure out if I should even have my plate and housing full forward or is that too much

AlpineRAM

For a starting point on a non stock setup this is what I do:

Remove boost hose from IP- turn AFC to a point where at a snap acceleration command only an acceptable amount of smoke is present. Then reconnect boost hose to IP, usually you are done, sometimes you may have to go 5 clicks loser or tighter to get the desired results.

Plate setting- I'd go for "manageable" EGT there - housing setting "full forward" eliminates the AFC function.
You need that AFC bugger limit the travel of the rack lever until there is boost- then the plate should limit travel.

J_dude

Thanks for the input! I will have to give that a try today. So housing should be all the way back then?

nascar mark

Basic's from my site that should help you - Dodge Diesel Performance - Dieseltuff
Keep in mind AFC has nothing to do with the fuel plate....that is an adjustment that needs to be dialed in after AFC is tuned & marked/scribbled so you can easily put AFC back in place after. As Alpine said, adjust fuel plate to your egt's & smoke tolerance.

AFC housing adjustment is a gross adjustment and starwheel is a fine adjustment. Moving the housing forward towards the radiator will allow more bottom end fuel (little to no load fuel) and back less. Adjust this 1st and get a happy medium for your setup. Then fine tune it with starwheel for final tip in fuel.

To adjust starwheel, use an 8mm allen wrench to take the plug out of the top of the AFC housing (near rear of inj pump). Then you can see the gear (starwheel) in there and all you do is turn it. A flathead screwdriver works best. If the gear is pushed towards the engine (moving up towards the radiator), the turbo boost will take less pressure to overcome the spring and you will get more fuel/smoke when you initial accelerate with low or no boost built. If you rotate the gear towards the drivers fender (moving towards the cab), it will take more boost pressure to move the AFC foot, hence less fuel tip in and will prevent less smoke on accelerating with low or no boost built.

By tweaking the AFC to just the right spot, you can get a good amount of spool up with a small amount of smoke. Adjusting for best acceleration = very little smoke (just a haze) out the tail pipe at heavy acceleration.

AlpineRAM

Yep, as nascar mark said- (i ommitted steps)- turn starwheel to a centered position on it's adjustment, then slide the AFC housing with the boost line removed until you get a still snappy but almost smokeless (tiny haze) acceleration. (Naturally your truck will "fall on it's face" as long as the boost line is disconnected) - after that basic setting, connect boost line and adjust starwheel to get the same light haze of snap throttle beginning through the whole motion of the AFC.
Nicely tuned you get very good acceleration with almost no visible exhaust, and your automatic trans can shift correctly.
A misadjusted AFC will throw your AT off it's tracks.

J_dude

THANK YOU! That helps a ton! So much good detailed info all at once! Somehow, in all my searching, i have never seen your site before.. lol. On one of the threads i read, can't remember where, a fellow said to set the star-wheel two rotations from all the way forward (against the front of the housing), as a starting point. Now my question is, how many clicks is a full rotation...?

J_dude

Another question; Where should the fuel screw be set while I'm adjusting the housing position? So it just touches the diaphragm inside like I read somewhere?

AlpineRAM

Yep, what you call the fuel screw is the lowest amount of fuel the AFC controls- so if you want to adjust the AFC you need to make sure it has it's maximum travel, but without any undue influences. (This would be different on a throttled diesel like Mercedes Benz, but for the Cummins you can do it on your workbench without additional tools.)

To get to the basics- you need air to burn fuel- if you build an injection pump your job is to inject enough, but not too much fuel for what the driver wants and the engine can burn. (and comply with environmental regs at that too)
So, in the case of the good old P7100 you have an AFC, a plate and governor springs.
Simplified it looks like that- for each rpm you have a certain amount of air in the cylinder, and you can add a bit of air if there is boost. Now you have to meter in the correct amount of fuel for a given situation. That's where plate profiles come into play- the plate does it's job when there is boost across the rpm range. Works fine, but if you change the governor springs the fuel lever inside the pump will read a different region of the plate at a given rpm. (unless you change the cam you will not be fine with just one of governor springs or plate)
If there is no or low boost the fuel lever is limited by the AFC plate long before it can go to the fuel plate- but it is still crucial to get the right profile and position there if you want good driveability.
It's a finicky business, but taking care there is very rewarding. (like outrunning the most modern CTDs while getting better fuel mileage)
Remember- soot is just diesel that you paid for that only ruined your environment for you and your kids, if you take care you get at least the same power with less fuel and less environmental damage.