AFC mod...attepted, may have missed something
 

Ok, so I started about 1pm today and I got the AFC housing off pretty easily. The breakaway wasn't bad it was the slotted one that gave me trouble. Anyway took that off and pulled fuel plate. I ground a #100 profile (flat with a radius at the bottom) into the plate and re-installed with it slid toward the front of the engine. My star wheel was already basically turned all the way touching the housing. Then I shaved about 1/8 in off the AFC foot shaft. I turned the "smoke screw" so that when the 2 bolt (one breakaway) access plate is removed that the threaded shaft with the internal allen head is almost flush with the jam nut. I did NOT replace the cups on the diaphram with washers because I didn't quite understand what was going on there. So I get her all back together and was thinking that what I had done would give me some more power and smoke but I didn't notice power changes and still...no smoke. And I know smoke is unburn/wasted fuel but I want it to kick some out, I got nothing. What did I do wrong? Any help would be great. thank you

I went out removed the silencer ring and noticed some debris in the inlet, then I found out why, I cant believe I never checked it, what a dummy:argh:, well I got some pics of the star wheel and AFC still no smoke though...

http://www.dieselbombers.cohttps://w...1&d=1352094170

the barrel of the foot or the blade of the foot? did you tune the afc as a unit with compressed air? you should have or all you did is totally screw the factory tune out of your pump. absolute best bang for your buck is a set of govenor springs. they will totally turn your truck into a different creature. a fuel plate wont give you that OMG my truck is so fast feeling AT ALL! you need supporting mods to notice much of any gain from a plate. a #6 was my first mod back in the day. a big $225 let down. but after much more extensive piddling with the truck i found it to be my best plate for daily driving until lately.

I shaved down the round part that the shaft slides into. No, I didn't use air, the wheel was already fully towards the front of the truck. I just figured I'd get more power/smoke for free, I just really don't see any difference at all. I want to get all the free stuff done first...and right then its the 4k GSK/60lb springs, 2095 plug and boost elbow for starters

well it sounds like you need to do your afc all over again. tune it this time just dont screw with the little wheels and ahinny things. LOL it will run better. do the washer flip so you get the extra bit of travel. it takes like 10 min to do if the afc is already in your hand. then use regulated air to tune the afc. i would buy an boost elbow and tune the afc for the mid 30's boost. if not you will be tuning again when you install the elbow. the rack plug only gives you a WOT increase.

I was just under the impression that if I turned the wheel all the way forward that it would fuel up no matter what boost was at, Im slowly wrapping my head around this stuff. Now those washers, the one that the spring seated in was cupped, with the cup going over the spring and then on the other side of the diaphram was just a flat type. So I can ditch both of those and replace with 2 washers? Is there a specific size or P/N so I get the right ones? Also is the rubber diaphram directional?

you can just grind the cup off the one washer and yes. there is a really good right up somewhere floating around here on the AFC

hope this helps

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

Ok, well it looks like the AFC is coming off again, ill grab some washers and a filter today at the parts store. What exactly does replacing the washers do? I really appreciate all the info!!

The lip on the Large forward cup bottoms out on the body of the AFC. Flipping them allows more inward travel.


To further explain the mechanism and its function....

The starwheel applies preload on the diaphragm. So when its farthest forward, there is the least amount of preload on the diaphragm. So less boost pressure will push the mechanism forward priming the fueling rail.


Black smoke is fuel the engine does not have the heat to burn... so its just further cooling your flame kernal, producing less energy.


So using air pressure allows you to time where your fueling rod dumps in, accelerating your fueling curve to match boost pressure.

Think of it as a Giant accelerator pump on a carburetor.

Technically, I think the "smoke screw" is the accelerator pump, allowing more mechanically applied fuel regardless of air flow to get things going, and the AFC is more of a vacuum secondary wich regulates fuel per air flow, if we're comparing injection pumps to carbs... :w2:

Negative Fummins.

The "smoke screw" is just a base preset. What that does is set the "0" resting position of the rack. The further in you screw it, is your base minimum level of fuel at any point. So if you have a setup that flows very high CFM at/off idle, you would increase this. Aftermarket turbos on OEM 160hp injectors, would increase this.... Larger injectors, would keep this backed out, and then use the star wheel to incorporate when flow is increased.


So really, the start screw is what your idle air screw would be.... ;]

Sorry Fox, but I disagree. The smoke screw sets the idle/zero position of THE AFC FOOT, NOT the rack....the rack can in fact back off boyond the resting point of the AFC foot. Hence, when you push the throttle, advance the rack, the smoke screw lets you advance it until it hits the foot when it would then be controlled by boost pressure. Also, CFM and Pressure are NOT the same thing.... but this is no place for arguing, and who cares about carburators on this site anyway??? :tttt:

Correct... your right, I used the wrong term when I said rack.... But overall my statement was correct. The smoke screw on the back of the AFC, does only adjust base fuelling point.

And yes, I know CFM is different than pressure. Hence why I used CFM. LoL.


I've done my share of engine porting and building Fummins. :w2:

So I took it off again today, I still have to use air to set the star wheel but once I got that access plate to the diaphram off again and started playing with it I saw how it was bottoming out and limiting the travel of the foot. So I flipped the one washer and put it on top of the spring and them used a washer I had on top of the diaphram now it allows full travel of the foot with the 1/8 inch I took off the end of it. The "smoke" screw, I loosened the jam nut and then with the access plate back on the diaphram I turned the allen screw in until I made contact with the shaft and moved the foot and then gave it a half turn and snugged the jam nut. I was playing with it for about an hour or so trying to understand how it all works and I think I have a basic understanding now...I think...I'm sure someone will let me know if I don't. I'm getting the 2095 rack plug from a local shop too.

Sounds like you're well on your way! :tu:

The AFC is an Aneroid Fuel Control....."Aneroid" meaning "by air", so Air Fuel Control, if you'd like. See the picture below. The little arm thingy in the middle is the throttle arm; it is attached to the throttle shaft and the rack shaft. It has a little foot on the top end that advances forward moving the rack (thus turning the barrels and giving more fuel). It comes in contact with the AFC foot and eventually the fuel plate, riding along the fuel plate profile as RPM's increase, thus the plate profile dictates WOT rack movement and can increase or taper off the fueling based on the peaks and troughs of the plate profile. The AFC (Air Fuel Control) foot stands in the way of the throttle foot and the "full fuel" plate during no- or low-boost conditions to prevent overfuling. As boost is built, the air pressure pushes the diaphram which advances the foot and allows more fuel to be added as per the presence of boosted air signal, ideally at the rate of just a mild haze of smoke if tuned properly. The "smoke screw" simply advances the AFC foot forward without air pressure influence and gives you that extra bit of no-boost fuel for takeoff, generally causing a bit of fuel dumping and thus smoke hence why it's called the smoke screw.

http://www.dieseldatabase.com/images...s/p_pump08.jpg

I have my smoke screw backed all the way off, but the AFC housing slid full forward, which also acts the same as bumping the smoke screw a bit because it's advancing the AFC foot in front of the throttle foot. I then tuned my AFC for mid stroke at 15psi and full stroke at 35 psi with shop air...I did this by attaching a blow gun with pressure regulator and dialing the pressure to 15 and 35, blowing in the diaphram port and adjusting the star wheel so the spring rate would produce the results I wanted. I have hardly any smoke and fairly smooth acceleration. I'm also running an "industrial" fuel plate full forward, which I believe is closest to a #12, for what that's worth.

Hope this helps! :c:

Thank you for all the information on the AFC, between what you guys have said and having it my hand and actuating it I think I have a grasp on it. But before I properly tune the AFC I have to fix the problem. I have ZERO smoke no matter what I do. There should be some no matter what but there is absolutely none. Something is clogged or broke, pressure or volume. I'm going to pick up a fuel filter tomorrow. I also stopped at a local diesel shop and they said there is a banjo bolt with a ball valve on the pump near the head, there is a spring in there that controls pressure, the old girl is in the garage right now so I think I'll go check that out. Any other suggestions?

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UPDATE: I got that bolt out, spring was intact and had 3 shims I'm not sure if its the proper tension though so I will take it to that shop tomorrow.

I believe that "banjo bolt" you are referring to is the Overflow Valve - OFV. Search it on here to find the pen spring mod you can do to increase the fuel pressure fed to the injection pump. Those OFV's wear out over time and get weak and can really hinder the pressure supplied to the pump thus reducing power by simply evacuating too much fuel through the return line. Tork Tek also makes replacement OFV's that have reduced orifices to keep pressure up. :tu:

I put a pen spring in the OFV and made sure that the ball was in there, did fuel filter too. Still no smoke. Going to try and run it off a fuel can tomorrow and borrow my buddies pressure tester. I gotta figure this out, Its driving me nuts!

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UPDATE: I pulled the return line and fired it up and fuel came out. Then I ran it off a gas can, same thing. It does start hard when its cold and sometimes dies, and idles around 500rpm I think. I am pretty sure its my pump...

i seriously seriously doubt its your IP pump it could be low fuel pressure from your lift pump? are the mods in your signature all you have done to the truck? if so you havent added much fuel and it ISNT gonna smoke much. things dont start smoking much till DV's, injectors, gov springs and big laggy turbos.

I was thinking timing? Rack hung up not allowing travel? Idle seems low. I don't know, I've been at this for 3 days and I'm stumped. Good thing the girlfriend likes the smell of diesel.

slipped timing normally = a really rought running truck with lots of white smoke.

Is there anything I can test or do to maybe isolate the issue?

TDC the engine and see if your pump tab slips in its hole. assuming you have stock timing

Guy before me said he advanced it 15 degrees. Ill check monday though since today is The Marine Corps Birthday and tomorrow is Veterans Day, I will be celebrating. Thank you for the help and I will get back to you guys with what i find out. Semper FI.

I ran a boost gauge to the block on the back of the AFC, I put it where the waste gate reference goes. I'm only making about 12 psi max. I think I'm going to remove the plate completely and see if that changes anything...

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Plate is gone, no change:argh:. Can a bad fuel heater give me these issues?

it will crack and spit and carry on most likely and be very hard starting if it is the fuel heater. if it is the lift pump it will have very low power like you are experiencing!

Ok so I deleted the fuel heater anyway since everyone says its junk and will eventually cause issues. The pre-filter was dirty and the gaskets looked pretty shot. Today I'm going to put a pressure gauge where the bleeder screw goes on top of the filter housing to see what kind of psi I'm getting to the pump. I was going to yesterday but my buddy with the tester got busy.

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+/- 50 psi @ idle, a bit more at WOT.

um??? stock lift pump?

Yes, stretched the OFV spring and inserted a bic pen spring, it had 3 shims on it too so I'm assuming that is while the pump pressure is higher than average. I'm heading back out there in an hour or so to pull the AFC back off so that I can look inside the IP, I think that I am having a rack issue. I'll try and get some picture of inside there so that you can see what I'm looking at.

I have removed the Bic pen spring, gutted the AFC, removed fuel plate. No smoke, no power, no change. Still maxing out at 12 psi and fuel pressure is back down within limits. Any ideas?

check your shutoff solenoid and see if it is fully engaging. after i put a plate in my 95 it ran terrible with no nothing and it turned out to be the shutoff solenoid was only engaging enough to start

How do I tell if its fully engaging or not?

The way I did, I turned the key to the run position and pushed the shutoff solenoid all the way up manually and it should pull all the way to the top and stay there on it's own. Mine was binding up and was only going part of the way up, basically it cut the power in half but when I would push it up manually and then start it, it ran great

Any updates?

It is always nice to know how things turned out/how the problem was resolved (or not).