Well, less wiring is definately better. It just seems so simple

I bet this could be done with a Field vtec controller even, no need for any of the throttle input.

Dustin

 

Ok, I need to think out loud and maybe someone can clear up my confusion With the previous hack, a MAP signal was run into the TPS of the AFC. This in essence gave you seperate vaccum/boost fuel maps (lo/hi throttle on the AFC). Now, I understand how running the AFC with it stock wiring (TPS to TPS, MAP to MAP) works. Since the AFC is cutting the MAP signal so much, the ECU thinks everything is kosher. But you're losing the ability to tune your fuel based on boost/RPM. I mean you can have fuel correction based on TPS/rpm, but you could be boosting 7psi at 4000rpms or you could be boosting 0psi at the same rpms. The AFC won't know the difference.

My thought is this. What if you combined the hacks? Run an unlimited MAP into the TPS and MAP connections of the AFC and set the lo/hi "TPS" crossover to your vacuum/boost crossover. This way you could have seperate maps... one for vacuum, one for boost. Wouldn't this give an even greater degree of tunability, but still keep the smooth transition into boost because of the unlimited MAP signals?

ADDITION: And yes, this should work with the Fields SFC/SFC-VTEC, just with less tunability. Anybody want to buy one, I've got an extra


[Modified by DSF, 12:28 PM 3/4/2002]

 

So for my NA setup. I can use either the Fields or Apexi AFC to idle my 450cc DSM injectors and run it smooth without major problems?? Just making sure before I make the commitment and buy one.

 

Uh, yes you can use a SFC, SAFC, VAFC, or whatever to attemp to idle 450's, but why? For a n/a set-up, 450's are way overkill According to how extreme your set-up is, I'd stay in the 270-310 range. Or am I missing a piece of the puzzle?

 

Well I have a type S hybrid. However I am using the saturated injectors that came with the engine, however I am using an ODB I ECU. Since I got the 450's for cheap I figured I could use them in the meanwhile, that is all. I would love to get my hands on a set of 310cc from the ODB I ludes but many people are trying to charge over $100 for those.. Again still dont know if its worth it but its something to do.

 

That's exactly how I set mine up. Thus far it works for me @10psi with -35% trim. I tried -30% but it was too low a trim and it wound up setting off a MIL for the MAP. So I lowered it to -35% trim, 10psi no problem I set mine up as follows:

1-4k= -40%
4.5k= -38%
5k= -36%
5.5-7k= -35%

Runs smooth so far

 

310's will not deliver enough fuel without using an FMU/RRR.

 

liam82,. what's the fuel presure set up on idle 450dsm? able to control hack safc.

 

Mine is 45psi @ idle. Stock FRP, 255lph pump.

 

Let me throw this at you, if you are using the AFC (VAFC) with bigger injectors only to reduce voltage from the map for lower injector pulse widths (factory maps), can't you just wire in a GM map sensor and a potentiometer to give lower map signals? It would even work with the stock map sensor. All you (we) are doing is dropping the output of the map voltage.

A $50 solution perhaps?




[Modified by G, 11:40 AM 3/4/2002]

 

I don't see why not, but you won't be able to make adjustments for differing engine loads at differing rpms.

Anyone care to comment on my previous reply (unlimited MAP signal into the TPS and MAP connections)?

 

You really don't need to. The whole point of this setup (which is why we leave it at one setting accross the board) is to let the ECU handle the fueling for different loads at different TP's.

 

Yeah, I guess that makes sense. I guess it's just the skeptic in me that wants the added adjustability. It's just hard to believe that the stock ECU can make boost/fuel corrections on it's own.

Hmm, now which do I sell...the VAFC or the SFC

 

Well, to the ECU, all it see's is an added amount of air in the manifold (under boost) and thus adds fuel accordingly. I guess the stock ECU is actually pretty good at "on the go" fuel adjustments, it's just the whole boost thing that it hates. So you just blind it's eyes from seeing boost and viola!! Trust me dude, it feels great! No more of that "hesitating/bucking" as it would transfer to boost suddenly, just one smooth seamless action.. I most definatley reccomend

 

I'm still trying to get my head around it. Could you explain it again?


[Modified by 5 Liter Eater, 1:39 PM 3/4/2002]

 

So where are the docs on how to get the AFC to read to O2 sensor voltage, and is there a quick reference somewhere on what voltages are lean, stoich, etc?

I hooked mine up today, and it works ok, but I think I'm running pretty rich in places...

 

It seems we have established that running an unlimited MAP signal into the MAP connection of an AFC works because of the amount of negative fuel correction required to idle 450's is enough not to throw a MAP CEL. Thus allowing the ECU to make the necessary fueling changes. But instead of using the TPS input for throttle based fuel correction, run the same unlimited MAP signal into the TPS connection. You would then set your low throttle % setting to where you engine goes from vacuum to boost (based on MAP voltage) and set your high throttle % setting to whatever your max boost is (again based off MAP voltage). This way, when off boost, you would be running off of the low throttle fuel maps. When in boost, you would be running the off the high throttle maps. So, between max boost and 0psi the AFC would be interpolating the corrected fuel requirements. Just like it does normally between x% throttle and y% throttle, but instead it will between @0psi and xpsi.

VTC_CiViC: I know your set-up works well and I trust what you say. I'm just looking for some extra possible tunability at no extra charge I mean, that is the whole point for the AFC thingamabobs

 

DSF:

I makes sense to me. It seems that you'd want to control fuel as a function of manifold vac/pressure more than throttle position. The thing is, since the AFC is expecting a TPS input of 0-5V and your MAP signal would crossover from vac-boost after 4.5-5V so you'd have to set your low-high crossover at 100% which would make the low portion be your vacuum range but you'd have nothing left for the boost portion.

Another thing is that the TPS input that you're feeding MAP output to is only used for determining what correction range (low vs high) to use, it's not graduated is it? So even though the MAP signal may be anywhere from 0-4.5V at anywhere throughout the RPM range the AFC would use the correction factor at the given RPM for the low range.

I should point out that I don't even have an AFC, I just think I know the general principal so feel free to correct me.


[Modified by 5 Liter Eater, 2:59 PM 3/4/2002]

 

Yes, that is correct. Fuel correction based on pressure, not TPS. But, your voltages are a little off. I just checked my VAFC's "sensor check" funtion. At idle (I forget how much vacuum) my MAP is putting out no less than 1V. At zero vacuum (engine off), the MAP is putting out no more than 2.88V. I would set my theoretical "TPS" crossover at whatever throttle percentage gave me @2.8V. So, from 2.801V-4.5V (@0-10psi-->stock MAP sensor) the VAFC would interperlate the correction between the hi/lo "TPS" settings. (Yes, the V/SAFC has graduated correction.) You could use a 2bar MAP sensor if >10psi was desired.

For those that don't understand my reasoning behind this, here is an example. Let's say you are running a fuel correction of -35% @4000rpms. This may be what you need as far as boost fueling, but what do you do if it runs rich off boost? You can be in boost at full throttle or part throttle, so actual TPS correction is basically worthless. With what I'm proposing, you could adjust boost and vacuum seperately. Just like the original AFC hack, just with the new added smoothness I think...

 

On what system is this?? On the V-AFC correction is based on your thottle position x rpm, vaccum isn't accounted for (if the V-AFC is what you're taling about )

 

Yes, the V/S-AFC. By integrating the original hack of connecting an unlimited MAP signal into the AFC's TPS input.

 

OK, that answers that. I did some more searching (forgive me, I know these hacks have been being researched for a while, I'm just now becoming fed up enough w/ my FMU to get interested) and what you're talking about is almost exactly what DBMAN96 talks about in "VAFC boost mod update!!" from November '01. The only difference is that he splits the MAP signal into the AFC's MAP input and lets the TPS input get an unaltered MAP signal. That seems to make the most sense to me. All the different methods take some grinding of the ole' brain gears to decypher what's doing what. One wires everything up the original way and takes 30-40% out across the board and one substitutes the MAP signal for the TPS input and starts out taking 40% out and taking 0% out at full boost.

I understand how the "wire as directed" method reduces the MAP signal enough to avoid a CEL in boost but I can't see how you can 40% out at full boost and still have enough fuel. I'm not saying it doesn't work, I just don't understand it. It also seems to me that you would stay in closed loop a lot longer since you're cutting the MAP signal almost in half.


[Modified by 5 Liter Eater, 4:43 PM 3/4/2002]

 

This appears to be the biggest problem with either approach - if you're reducing the MAP signal enough that it doesn't CEL on you, it will remain in closed-loop until you get up to max boost (where the MAP signal will finally hit 2.8x volts and throw into open-loop) or you put your foot to the floor (WOT). This is why I put a DPDT pressure switch into my system to trigger a 4.5V WOT signal as soon as I cross into boost (around 0.5 PSI, adjustable) which smooths things out enormously and lets me boost at part throttle all day.

 

Ah, Rafe's TPS mod would indeed take care of the open/closed loop problem. I think I may be down for ditching my 310's and Cartech in favor of some 440's and VAFC to start playing with these concepts. I figure it would only cost me <$100.

I still need to decide which method is better but both seem to offer the smoothness I'm lacking.

 

Just my observation - using the MAP -> TPS input on the VAFC makes full-range adjustments VERY simple because all you need to do to move the whole fuel map around is change the lo/high throttle switchover points. IE if you have it set so 90% is "hi throttle" and you're running rich, move it to 95% and it scoots the whole fuel map down a little. If this doesn't make sense, I am going to have to draw up some diagrams and make a little web site about this whole VAFC business and all the different "hack" approaches we've come up with.