AFC Starwheel Spring Curves
 

Installed DDP1 50hp injectors in a 180hp 1996 4x 2500 with Banks Power Kit, HTT exhaust, ATS transmission, GV overdrive. I can controll smoke and pass the snap throttle test but it smokes excessively with full throttle accelleration. I have moved the Fuel stop plate (Banks Ottomind) .030 forward of the OEM position to contain full throttle smoke with no apparent effect.

I have tried all the TST springs to no avail and am back to the OEM spring which seems to work best for my condition

Got any ideas on how to contain the full throttle smoke?

Have you ever touched your smoke screw?

hummm, the TST AFC springs are supposed to do a decent job in controlling smoke.

more air

I have been working with the AFC trying to control smoke. Using a Bicycle strut pump/gage hose and fittings I tested the AFC to determine how the different springs effect the AFC operation. I purchased the TST springs to see if there were any effective smoke control measures which would address my problems. I also tested the springs to determine what their spring constants were for comparison purposes. I found the following.

TST Light(K=39lb/in, L=1.48"), Medium(K=68lb/in,L=1.48") and the OEM(K=72lb/in, L=1.16") springs. The spring constants(K) for the Medium and OEM springs are roughly the same. The difference is in the spring length(L). The longer TST springs provide for a greater spring preload to offset the intake manifold pressure where AFC fueling starts. This contributes to turbo lag as the turbo has to overcome the preload tension of the AFC spring so it can start increasing fueling. There is a bootstrapping action with fueling providing greater exhaust pressure/heat energy to get the turbo going to feed more pressure into the intake manifold.

The AFC movement vis manifold pressue deflection curve shows that the star wheel spring tension adjuster just moves the spring curve up and down the pressure axis. This is a pretty rough way to achieve smoke control during fueling and maybe adequate for static fueling. Unfortunately engine loads cause fueling to lead the engine capacity to burn the fuel leading to lots of smoke during accelleration. With a rapid increase in turbo speed and manifold pressure during accelleration the AFC moves the fuel injection pump to the fuel stop plate limit at about 15psi of manifold pressure for the OEM spring. Then running under a static load manifold pressure drops back so the fueling then is determined by the AFC control spring as it balances fueling against load. So it appears that smoke control for accelleration under load has to be done using the fuel stop plate.

Unfortunately tailoring a stop plate is beyond my capacity.

If some one out there has gone through this process and has come up with a fuel stop plate which would address my problems I would sure appreciate an input. I could use a good P7100 pump man if there is one here is southern California.

I am looking for good low end HP/torque and maximum fuel efficiency. I have a 10K 5th wheel which I pull with this rig and we also use this truck for our long trips out of town.

Unfotunately this is a bit beyond my knowledge so I dont know what to tell you. Im not real sure pump mods will bring the results you are after. Going with a bigger/badder turbo (as whitmore said) should clean the smoke up nicely.

Can you pass a smog test right now?

What are you running for a plate?

I dunno which plate will do ya best but they certainly arent hard to tune up.................I build a 100 plate for my sons 94

some where here is some plates to gander at .........I will see if I can find em

here is some plate info

https://www.dieselbombers.com/12-val...-profiles.html

I think the smoke screw you are referring to is the stud screw on the back end of the AFC housing. I checked the set point of this screw and it was set at the limit of the AFC diaphram movement back. This should be the most lean setting. This is also the fueling at the idle point of the engine. If I were getting allot of smoke during the throttle snap test this would be a good adjustment to use. However, I don't have any problem with the throttle snap test just accellerating under load.

Thanks for your input.

---AutoMerged DoublePost---

The AFC OEM .030" orifice, which delays onset of fueling, should allow the turbo to spool up before onset of excess fueling with accelleration. When I had my timing set the well meaning pump man drilled out the orifice fitting to 1/8" effectively removing the orifice. I subsequently machined an "O" ringed orifice to replace the .030" orifice and that didn't help. I also tried a .040" and .025" orifice thinking one of these would help. Neither did. It seems that you can't get more air without more fuel and if you get more fuel you get more smoke. I suppose that the other approach would be with a turbo with the ability to build manifold pressure faster than the the PDR HX-35/14cm I now have. I still have a 12cm housing which might help but then I would be having problems with exhaust temperatures during towing. Unfortunately selecting a turbo is somewhat like going forward blind folded because there is little data on on most of the turbos being published. Most turbo/housings run to $1,000 to $2000 so cut and try would break the pocket book.

Thanks for your input

---AutoMerged DoublePost---


If the only road smog test is the Throttle Snap Test which is the diesel smoke opacity test of 40% opacity I shouldn't have any problem. This no load test includes the following:

The engine is held at full throttle for approximately two seconds, the released. This is done 5-6 times, with the first 2-3 times being considered invalid, as built up carbon being blown out of the exhaust may show darker smoke. The initial burst of smoke from the next several accellerations is simultaneously compared with a tinted plastic sample while viewed against a white background under daylight conditions.

However, I understand from postings that the highway patrol also is monitoring smoke produced under highway driving conditions. This may be a problem for all who generate smoke during accelleration and that is my concern.

I am running a Banks Ottomind fuel plate which came with my Banks Power kit.

Thanks for your questions.

---AutoMerged DoublePost---

That is an excellent posting of fuel plates. However, there is a problem of matching the right fuel plate to an engine load profile. Do you have information on what fuel plate would work best for pulling a 10k 5th wheel? Steady load and accelleration loads. Using a 3.54 dif, ATS transmission and converter, Banks Power kit equiped engine with HTT exhaust manifold and ATF air intake.

Thanks for the great fuel plate site.

I dont know how you guys live with all the laws and rules in California.

I hope you can get it figured out. All I can suggest is a more appropriately sized turbo for yours fuelling mods. Good luck - I hope you can get it figured out - most guys want more smoke and you want less...lol

I would move the AFC housing back if you havent already and/or back out your zero boost screw completely. You should not be able to create enough boost on these revs to even move the AFC. This fueling is done at the zero boost position and and by the governor. If the governor springs are enough to overpower the rack spring, it will over fuel more than it should on zero boost shots.

See, somebody knows....lol

The AFC housing was already set back as far as it would go in the OEM position and I left it there for this installation. The zero boost set screw is already set at the minum point before the OEM spring starts floating so I left it there. I would hesitate to even completely back out the AFC with the TST springs which would place the spring preload pressure on the AFC's silicon rubber diaphram. That constant pressure would be bad for the diaphram and would cause it to creep back as it stretched and it could ultimately cause it to fail. Better to use the zero boost set screw to limit the diaphram movement to a safe range.

I just received issue 60 of the TDR register and in there Joe Donnelly gave the case for twin turbos and outlined the limits of a single turbo on page 96. To quote him:

"As you increase the horsepower from the factory setting you have to size our turbocharger so that drivability is adequate with responsiveness and low smoke, yet a power increase is supported. As the power increase gets bigger and bigger, the compromise becomes more significant. We accept slower spool up and the need to moderate the accelerator pedal to keep smoke down. We also accept that the turbo ends up smaller than would be ideal...."

I had to move from a 12cm turbo housing to a 14cm housing to reduce my EGT temperature while towing my 5th wheel trailor. This tracks with the compromises that Joe is talking about. Accordingly my problem appears to be a fuel/air balance problem at high RPM/Boost during accelleration. I have taken two 200+ mile trips, without my tralor, since I did this installation and had no problems under steady state run conditions. It was only on acceleration under load where fueling got ahead of the turbo resulting in smoke. This tracks with what Joe Donnelly is saying. His solution is to combine the quick response of a small turbo with the higher air capacity of the larger turbo to increase the transient and run response of the turbo system. As he points out it is a costly solution however, in the long run he has nickel and dime'd his way past the cost of a well designed twin turbo from a vendor like BD.

I have yet to try the system with my trailor. At this point I hope the system will work well. We shall see.

Thanks for the update - sounds kinda like what we said at the start - you need more air.

The BD Towing Twins are supposed to be great for towing. BUT, like you said there is substantial cost involved. Many guys are fabbing up their own twins using a HX on top and a S400 or something similar on the bottom. Yeah, this would not be tested and balanced like one of the "diesel shop" sets of twins, but it will give you a while lot more air to clean up the emmissions as well as a huge performance kick in the pants. You will likely need some head studs and o-ring/fire-rings etc. Why not do twins you already have a good tranny which really is the starting point for twins.

When I did the spring install and AFC foot modification, I did not observe the same "stretch" you described with the unit set for minimum fuel at zero boost.

However I do agree, as would any with mods, that the fuel is the easy part. Getting your boost air flow to match your fueling is the tradeoff of lag, flow and overall performance. Compounding stretches out the useable air map of the primary turbo and fills in the holes for spooling vs. all out flow. I can drive with little smoke, but its just a little hard to keep up to traffic waiting for boost. Consiquently, my turbo is also a little small and chokes me out at high RPM runs (read 1500 F temps :booo: ).

Again, the fueling should not be harsh enough at zero boost to cause large amounts of smoke.

I don't know if you worded this wrong, or thought wrong or something, but moving the plate forward (toward the radiator) is going to increase fuel and smoke. That could be part of your problem.



My recomendation for a smoke free 180hp truck would be this
1. make sure you valves are adjusted properly
2. make sure pump timing is set close to stock
3. #8 fuel plate, in stock position (or possibly a #6)
4. Afc housing in stock location
5. Smoke srew in enough to take up the slack on the afc rod
6. then fine tune your acceleration smoke with the various afc springs and spring tension (probably stock spring)

Other thoughts....
The banks plate I have a pic of looks very similar to the #5 plate and the maximun EPA certified plate for a 180hp truck is a #8 (EPA certified to me would mean no smoke). Now don't get me wrong on this, I don't think EPA should be able to tell us how much HP we should be allowed. But that might be a nice smoke free plate, and combined with your other mods should make for a nice towing truck.

Hope this helps....Josh