Engine/Transmission (1994 - 1998) AFC adjustments

[PetesonM]

There are several adjustments in the AFC housing and being fairly new at this and am trying to get a feel for what everything does. I hope this will turn out to be a good thread that can help others in my same situation.



On the attached picture there are several places circled and lettered. So now lets start the questions. The idea is to correct my errors in this post.



1- I went with the AFC spring kit which includes two springs both the same length but one is tighter than the other. The loose spring will give more low end fuel and smoke since the boost overcomes the spring at a lower PSI.



2- The star wheel (letter B) when moved forward or to the left in this pic adds more to the low end fuel/smoke again by effecting the spring tension.



3- The bolts in area "C" are just the cover bolts to cover the part marked "D"



4- "D" is something I am not too familiar with I believe this sets the spring tension as well. The AFC kit said to just tighten it till it just made contact then lock it down. Should it be tighter than that? I would think not since you can adjust the spring tension with the star wheel but like I said I am new and this seams like a redundant adjustment to the star wheel.



5- Moving the housing. I assume this means moving the entire housing (held down by the 4 bolts to the pump itself) forward or back. Forward will move the AFC/govenor lever forward and allow more low end fuel/smoke. Correct?



6- On the front of the AFC there is the eccentric that is marked "A". What the heck does this do? I tried to center it when reinstalling but I am very curious as to what this does. Please explain.



Other than that, and getting away from the AFC there is the govenor lever adjustment. I already have that set so it contacts the bottom of the #10 plate as it should be. I also have the fuel plate slid full forward for testing purposes right now.



7- I checked the throttle lever and it was still at the 5" as specified what does changing this do?



I know this got long but if this works this could be a good tutorial for myself and others as to how to tune these 'simple' little 12v's

 

[Signal73]

Part A dosent appear to do much, looks to me like it could center the AFC foot if it were out of adjustment, or facilitate its removal if you were to gut it...



Part D is the pre-load on the afc foot. screwing it in moves the afc foot in further allowing the gov. arm further travel pre-boost.



#5 is correct.

 

[PetesonM]

AFC housing

Okay my theory was to move the AFC housing all the way back to reduce, as much as possible, the 370's haze then use the soft spring and the star wheel to make sure fuel came on as soon as possible under low boost. Turns out if you have it all the way back the motor will not start. So how do you adjust the housing itself? I was playing around, move it forward, start the truck then slide it back till it wants to stall or gets a lopey idle. It almost acts like an EGR system on a gasser. Where should I set this thing?

 

[Signal73]

I dont think any afc adjustment will get rid of the 370 idle haze, thats an injector thing more then afc adjustment. As far as where to set the AFC, try centered and fine tune it with parts B+D

 

[bmoeller]

Sig73 is right. The injectors are the cause of the haze. They don't have the right spray angle for our pistons. They are marine injectors. Need to get extrude honed or EDM injectors.



I had 370s, but the DDP4 as bigger, cleaner (including no haze) and run cooler.

 

[Matthug]

Yup part A is just where you take it apart to gut it. Part D is the smoke screw, signal73 is correct in what he said about it. It gives you more preboost fuel which in turn spools the turbo faster BUT leaves more smoke out. Mine is in all the way hehe.

I just had my AFC off today and found several things out. The AFC arm wasn't getting full travel. Having put in an AFC kit already I was familiar with the diaphram and how it is set up. So I took it apart and found out what was stopping it. Well, there's a washer directly under the the actual diaphram rubber part that is flared out and it hits the housing. I found a similar sized washer with the same size hole and installed it in place of the flared washer..... and now I have 1/4'' longer travel. Whether the AFC arm wasn't moving far enough I'm not really sure, I have a 0 plate full forward so it kinda concerned me as it didn't seem to move much more than 1/2''. Now it moves atleast 3/4''.

Also, I put some shop air to it and found the AFC arm WITH THE LIGHT SPRING from the TST AFC kit doesn't reach full travel until 30 PSI!!! Yeah it starts moving with a couple PSI, but not full travel until 30! So, I'm gonna go to a hardware store or home depot whatever and find an even lighter spring to hopefully have full travel by atleast 20 PSI. This would make it much more responsive and faster spooling I would think. I don't really get how it could not have full travel until more than 30 PSI though, I mean the stock one is like 16 PSI. Does anyone know why the TST spring is about 1/2'' longer than the stock spring? That would kinda defeat the purpose I would think since that puts more tension on to start with. I almost feel I should put the stocker back in!

 

[bmoeller]

I almost feel I should put the stocker back in!

Maybe you need to just leave it out.