afc pressure line

[ptmoore]

I replaced the u-tube from the intake to the afc housing with a replacement tube from cummins dealer. the old tube was metal about 3/16 or so id. the new tube is plastic about 1/16 id. this change seems to slow the rate of fueling as the boost rises. i notice less smoke but slower boost rise. anyone else run across this also? am thinking i might repair the old tube and put it back on because i liked the acceleration rate better. any thoughts?

 

[JLEONARD]

What you say makes sense... you have to fill the chamber and a smaller line means more time to do that.

Can you put less spring tension on the diaphram by turning the starwheel down? That might help unless of course it's already adjusted.

 

[Greenleaf]

The AFC is an "add on module" It simply isn't needed. Many pumps don't. Adjust the pump properly and you simply chuck the line. Install a 1/8" pipe plug in the head and one of the small clear plastic plugs found in the pump seal kit fit's into the AFC air port.



Acceleration rate won't be an issue.

 

[ptmoore]

thanks for the replies. Jleonard i still have some adjustment on the starwheel so i may play with that. Greenleaf, not sure if i want to load six yet[shootist] but you can be shure i will play with that idea also. KEEP ON SMOKING

 

[Joseph Donnelly]

Check the brass fitting that the tube goes into. You may have a restrictor (very small hole through it) in the new one and a larger diameter hole in the old one. You can drill out the fitting for faster response of the afc vs. boost.

 

[ptmoore]

hoseph, the old tube and fittings are MUCH bigger id than the new one

 

[ptmoore]

sorry, i mean joseph

 

[dpuckett]

ptmoore- check out my post in the "discontinued parts" forum from about 2003. I used 1/8 OD air line and have had no problems.



The Cummins replacement I got was the same ID as the OEM pot metal line.



Joe D- what is this about a restrictor? I'm



Daniel

 

[ptmoore]

thanks dpuckett, i could redo the old line but with the boost fuel coming on a little slower the exhaust smoke is considerable less. going to tow the boat to the lake in a couple weeks and see if it is still white when i get to the lake this time:-laf:-laf:-laf

 

[Joseph Donnelly]

Ppump afc's use a fitting at the pump with a very small orifice to dampen the effect of changing boost. A full diameter hole would allow faster response of the afc to boost changes.

 

[Niki]

The AFC is an "add on module" It simply isn't needed. Many pumps don't. Adjust the pump properly and you simply chuck the line. Install a 1/8" pipe plug in the head and one of the small clear plastic plugs found in the pump seal kit fit's into the AFC air port.



Acceleration rate won't be an issue.

I have a few questions about this. Does the AFC add fuel on top of what is already there with boost pressure doing something, or does it control the curve of what has already been adjusted for with the fuel screw? If you remove the AFC and/or grind the lever, will it smoke like crazy if you get in the gas too quick? I've heard of P pump guys putting a "Valet" on their AFC air line between the pump and intake with an adjustable valve to control EGT when towing. I was thinking of doing this when I tear into my next first gen's pump.

 

[dpuckett]

I think Greenleaf bypasses the AFC internally, basically making the guts of the pump as if it were an industrial non turboed pump/ governor assembly. LOTS of smoke if you dont drive it properly- there is full fuel available at all boost levels (or as much as the RPM will allow). GL, correct me if I am wrong.



In stock, functioning form, the AFC cuts fuel til more air is available to burn the fuel. As more air comes on, more fuel (potentially) gets added. You normaly get half to 2/3 your full fuel at no boost.



The valet switch the p-pumped guys install, and some VE'd guys, too, cuts off the additional fuel that comes with boost. It basically does the same thing as cutting/ unhooking your AFC tube (not hard to do, and is usually done accidentally). Normally, you start out with about 1/2 to 2/3 full fuelling, then gradually increase to full fuel as you get more air (boost) to burn the extra fuel. It is a smoke control device.



Joeseph Donnelley- thanks for the explanation. I dont think it applies to the VE, as the banjo bolt at the AFC is just that, a banjo bolt.



DP

 

[NYCEGUY01]

When I installed a valet switch I used plain old 1/4" air line from the local hose shop.



Bought a 1/8npt to 1/4 pushlock fitting for the motor side then drilled and tapped the afc cover to 1/8npt where the banjo bolt used to be. Then had to use a 90 degree elbow with another 1/8npt to 1/4 pushlock.

After that just plugged in a little 1/4 nylon hose.



I think 1/8 line would be sufficient but the 1/4 seems to be working fine with no problems. The fuel comes on real fast with the boost.

Maybe the 1/8 would help slow it down a little but thats what the valet is for anyway. lol



With the valet off the truck drives fine empty and no matter what I do the egt's wont go over 1150

 

[PToombs]

I can tell you with a whole weeks experience that with 370's, the valet only slows down the smoke, it doesn't stop it! :-laf

 

[tugboatphil]

Niki,

Greenleaf did my pump. I have run it for almost two years. PODs, larger turbo impeller, AFE air filter, 4 inch exhaust from the downpipe. Excessive smoke is not a problem. Believe me, I sometimes wish I could make a lot more than I can. If the head of EPA was right behind me in traffic, I could have pretty fair acceleration without noticeable smoke. However, if a 25 year old Volvo full of hippies was next to me in traffic, I could fill the inside of the car with little effort.

I don't really understand why I can run without that tube, but I can.

 

[Niki]

Well, the way I understand it there is no real advantage to running without an AFC for most people, since an AFC is somewhat tuneable. I would think running without an AFC might make hot EGT's when towing a problem also. My last truck I had that I drove daily, I threw a governor spring in and turned the fuel screw in a few, but actually backed off the afc starwheel. I gained a couple mpg, but it still got up and went when I stood on it, made 30 psi with 18. 5 housing and stock injectors. The next truck I'm going to play with is a 5 speed intercooled W250 that I'm going to put a HTT 62-12 and POD's on, along w/ the usual 366 spring, exhaust, BHAF, etc. I'm going to put a valet on it and see what happens, I may just bottom the starwheel and use an adjustable valve inside the truck and see what happens.

 

[Greenleaf]

I think Greenleaf bypasses the AFC internally, basically making the guts of the pump as if it were an industrial non turboed pump/ governor assembly. LOTS of smoke if you dont drive it properly- there is full fuel available at all boost levels (or as much as the RPM will allow). GL, correct me if I am wrong.

DP

Yes. And as some have found the existance of the lever inside the pump (reverse) limits the movement of the governor assy thus the sleeve which limits fuel. It woulkd act as an internal stop if you will.



Correct, the boost signal line is open. No restriction as I have on the fleet of P-Pump engines.



GL

 

[bgilbert]

Yes. And as some have found the existance of the lever inside the pump (reverse) limits the movement of the governor assy thus the sleeve which limits fuel. It woulkd act as an internal stop if you will.

So the million dollar question. . Is there HP to be had by removing the afc lever completely? I know there is by way of grinding it. Seems as though without the afc lever, there's nothing to push the fuel pin out against the fuel cone. Is this just acting as a non-afc industrial type pump?



Here's my experience with a ground afc lever vs. stock afc lever, copy/pasted from .org site.



I pulled my half ground afc lever/foot, installed a stock afc lever. Lost at least 10psi of boost . Previously would peg the 60 lb gauge. Now only 50psi. Fuel screw reinstalled in exact same position. Installed a somewhat ground afc pin/cone gained 2psi. The only other change at this time was, I got rid of the metal afc tube that runs between cylinder head and VE. Replaced it with 1/8 tubing and fittings. Pressure tested to no leaks. Then checked for leaks with engine running and the 'ether test'. Spray starter fluid on all air connections, engine will rev up if leak exists.



Also the truck does not pull near as fast above 2k rpm. To say the least I'm not real happy. Spent the better part of a day fooling with grinding off the epoxy on the roll pin and ball bearings, then pressing it out and pump top R&R. That was mostly my fault as I wasn't sure how to remove the lever. Won't take half as long now to swap.



I think I'm gonna finish grinding the rest of the toe off the afc foot, pull the stock lever and install the ground foot/lever or not even install the lever at all??...



Back to the topic:

I'm using 1/8 tubing now instead of the bigger ID metal afc tube. I'm wondering if this had anything to do with slow boost coming on, less boost, and less overall get up and go. . ? Guess I could swap the metal tube back in for comparision.

 

[Greenleaf]

I told you when I gave you that lever... ... ... ... ... ... ... kids, &%$@!@$



Why on earth you think I remove them... ... ... ... ... ... . LOL

 

[paccool]

FWIW



I just replaced the stock metal line with 1/8"poly tubing and the boost is slower to come on. I am going to go the1/4" tubing route but want to stay with the plastic and make it long enough that I can easily pull the top of the pump off for tuning. Already got the TPS removed so it is getting a lot easier to remove the bolts. I also got SS allen head screws so I can use along allen wrench. Gotta be careful as those threads on the pump are easy to strip out.