AFC tuned, now truck doesn't want to start/run?

[dennhop]

So I finally got around to retuning my AFC yesterday, for the new turbos. I took the AFC off, checked the fuel plate (which is a 100, btw), and started tuning. The plate was already full forward, so I left it there-I figure with it being a 160 pump, it can use all the help I can give it. I set my air compressor to roughly 65 psi, which is what I know my max boost has been, and used my blowgun to pressurize the AFC. I then took it a slight step further than normal, and used a set of calipers to find at what point I had the most travel on the rack. Once I had the AFC starwheel adjusted for max travel, I then took the fuel screw, and backed it out to where it was just barely touching the back of the foot at rest. Once I did all of that, I went ahead and put it all back together. I also did an oil change at the same time. I love that quick release drain valve on the pan-so much faster! Put everything back together, and started it up. It had a hard start, almost like it wasn't getting any fuel, and I hopped out, started looking at a few things, and realized that I had forgotten to hook up the boost reference line. Got that tightened up, and tried again. After a few more unsuccessful tries, I went ahead and checked the fuel at the injectors, bleeding 1, 2, and 3. This morning I went to start it up, and it didn't want to start. I finally got it running, with copious amounts of accelerator, and started driving. Fuel pressure is around 30 psi, so I know I've got fuel to the pump, but for the first few minutes, if I let the rpms drop to idle (ie shifting, or just sitting) without giving it gas, the truck would die. Once it warmed up, it seemed fine. The truck runs a bit better; my boost hits 50 psi and I'm only hitting 1500 on the pyro, as opposed to hitting 1600 by 30 psi before, and now it's a light haze at full throttle, as opposed to dumping clouds of smoke out. It seems to me like a fueling issue. The only thing I can think of is that I've got a posi lock cable for my fuel shutoff, and it's attached to the mounting bracket that sits over the bottom two AFC mounting screws. If that got tweaked, just enough to put tension on the cable, could that not be allowing the fuel shutoff not to come up far enough? I think it would seem a little off, and I shouldn't be able to hit 50 psi if that was the case. Pulling the AFC off, I can't see anything that would mess with the fuel, other than that, and it seems to me to be a fuel problem.

[ISX]

I set my air compressor to roughly 65 psi, which is what I know my max boost has been, and used my blowgun to pressurize the AFC. I then took it a slight step further than normal, and used a set of calipers to find at what point I had the most travel on the rack. Once I had the AFC starwheel adjusted for max travel, I then took the fuel screw, and backed it out to where it was just barely touching the back of the foot at rest. Once I did all of that, I went ahead and put it all back together. I also did an oil change at the same time. I love that quick release drain valve on the pan-so much faster!

Can you explain that in more detail? Also the AFC moves at like 5psi so why did you use 65psi?

[dennhop]

What I mean by that is I set the fuel screw depth so that at rest, the screw just barely pushed the AFC foot forward....basically so that it was just making contact with the foot when the foot is all the way back. As far as setting the foot to 65psi, my understanding of tuning the foot is that st max boost, the foot should be full forward...maybe I got it wrong, but I set the tension on the star wheel so that at 65 lbs of pressure, the foot would be fully forward. I tightened up the spring so at 65 lbs of boost the foot didn't slide all the way forward, and then loosened it up a little at a time, checking the forward travel of the foot until I felt it had slid as far forward as it could at 65 lbs of boost.

[ISX]

What I mean by that is I set the fuel screw depth so that at rest, the screw just barely pushed the AFC foot forward....basically so that it was just making contact with the foot when the foot is all the way back. As far as setting the foot to 65psi, my understanding of tuning the foot is that st max boost, the foot should be full forward...maybe I got it wrong, but I set the tension on the star wheel so that at 65 lbs of pressure, the foot would be fully forward. I tightened up the spring so at 65 lbs of boost the foot didn't slide all the way forward, and then loosened it up a little at a time, checking the forward travel of the foot until I felt it had slid as far forward as it could at 65 lbs of boost.

Where is this "fuel screw"? I know of several screws all over the pump so I want to know which one. As for the AFC controlling boost, that isn't the intent of it. It is only there as a way to hold back the fueling arm until enough boost is built to allow for more fueling so that it doesn't smoke out the intersection. That means it limits fueling until the turbo builds at least 5psi. I set my starwheel full forward so it sets the tension very low so it moves at more like 3psi and might be fully out of the way at 5-7psi. Never really tested it. But thats the principle of it. The fuel PLATE is what limits the top end, and therefore the boost you're capable of. If you are using the AFC to limit boost, then you aren't using the fuel plate at all..

[dennhop]

Fuel screw im talking about is what most people call the smoke screw..

[ISX]

Ok you say you backed it out to where it was just barely hitting the foot rest, which is the AFC housing if I am thinking about it right (I don't have my AFC here, or anywhere, sold it haha). That means it must be farther forward in stock position. If you moved it back, then it could be holding the fueling arm back a little and causing the hard starts. You can actually take the AFC off, hold the FSS lever up with something and see if it starts right up, that will tell you right then if the AFC is holding something back. There is oil in there but it doesn't really "fling" out unless you rev it up, and even then its just some drops. I have watched mine a ton of times. Just make sure nothing like a hose clamp falls in there haha. But I am betting that is what's happening..

[dennhop]

That's exactly what was happening. I ran out at lunch really quick and cranked the smoke screw I. a few turns really quick. Problem solved. I'll have to go back in a fine tune it again later, to see where it should be sitting at, but between your explanation and another friend explaining how it all tied together, I'm starting to get it figured out.

[ISX]

Yeah the AFC should only be used for fine tuning the preboosted fueling. Once there is boost, that thing should be shoved to the far end and never show it's face again. It should move past the fuel plate so the fueling arm hits the plate meaning your boosted fueling limits are now determined by the fuel plate. That is why you have all these plate contours. A #10 plate eases into the fueling and then eases back out on the top end. A #100 eases in then stays into it. #0 is completely flat for max fueling, though the plate still limits it so people take the plate out completely to get even more.