DUDE!
YOUR A GENIUS!

 

This is great and keep us posted please on what happens, also those guys with 2 map sencors let us know what goes on.


This is very cool and I think i'm gona do it too.....

 

As soon as I get my home PC working better I'll post all this on a separate web page with diagrams and more info as I get more results - anyone else who tried please keep me posted!!!

 

looking at that diagram, i would have the outgoing map signal from the afc
going to the J&S in order to keep the AFC from giving a greater than maximum
voltage to the ecu and causing it to throw a code.

 

Right, *or* you could use a 2nd MAP sensor.

 

I did it the other way around and am just being sure not to use any positive adjustment from the VAFC. If you put the J&S AFTER the VAFC, you could have a whole range where the VAFC is recieving a positive map pressure, modifying it to change the fuel, and then the J&S is capping it and losing the whole result of VAFC tuning. The way I diagrammed it you should use fuel pressure and injectors to establish a condition where your fuel system will deliver enough fuel for max boost, and use the VAFC to trim that down.

 

Well, if the J&S is capping it then the signal is too high anyway. If the modified
signal is still higher than acceptable then it still wont do anything for you.

 

I don't think you're understanding my intentions here. The VAFC is recieving one MAP signal to its map input and another one to its TPS input. The map input MUST be limited to below 3 volts or any tuning done by VAFC will be pointless. So the VAFC MUST recieve a voltage-limited MAP signal, whether it be from the J&S or a black box or whatever. The MAP signal I'm sending to the TPS sensor can not be voltage limited or it will also be useless.

 

Oh ok. I forgot that you are not running any check valves or missing link.

 

Yeah unfortunately that is the big limitation - the need for an electronic MAP limiter at some point. These guys are trying to set up with two MAP sensors though; one will be on a missing link and the other will be free to read boost.

 

still limited to 12psi if using a stock map sensor though

 

I honestly think 12 psi is a very reasonable limit before you should start seriously thinking about something better than ghetto-modified VAFC fuel controls.

 

agreed

 

dbman, did you have any problem running 440cc injectors on your car? I'm assuming you needed the RC clips to plug it into the harness right? Aside from that and the tuning with the VAFC, it's no problems right? I plan on setting up my fuel system like yours, basicaly a royal overkill of fuel being limited by the VAFC to provde stable idle and low throttle driving. Just wanna make sure I don't have any nasty supprises headed my way..

 

I'm actually running DSM 450cc injectors; so in addition to what you said, I've got a big 10-ohm 25-watt resistor patched into the RC plugs. Aside from that it's plug and play; at idle I'm trimmed about -40% on the VAFC; I put those babies in and the car fired and idles on the first try and has never given me trouble in the 3 months since that. Sometimes takes a little longer to start but I think that's cause the VAFC takes a second to come up to speed. Anyway, it's been a real easy setup for me.

 

Ahh I see. Well I've got my eye on some RC 440's. They're labed as "saturated, for B-series motors", now I know they'll fit fine in my rail but do you know if, even though listed as saturated, I still need these RC clips for OBD-II? I'm guessing yes but I wanna be 100% sure.

 

You will definitely need the clips for OBD-II

 

Hey I have a question on this.

Now...let me understand this correctly.
So...you hook the MAP output into the TPS input of the VAFC...so when the manifold pressure rises...the VAFC thinks the throttle is increasing...correct?

Now...how do you make that add fuel?
I have an S-AFC...and thought you can only add/subrtact fuel at different RPMs...not at different throttle positions.

 

I dunno about the SAFC since I've never used one, but the VAFC has two fuel curves: narrow throttle and wide throttle; each one has several RPM points on it. The VAFC interpolates between those at different throttle positions between 0 throttle and 100% throttle (but now at different manifold pressures rather than throttle positions).

Update: I just checked out the SAFC manual and it looks like this mod would work exactly the same on the SAFC as the VAFC. This whole throttle position thing is explained pretty clearly (well, as clear as an Apex'i manual gets) in the manual which is available on http://www.apexi-usa.com




[Modified by dbman96, 10:06 AM 10/12/2001]

 

Yes the S-AFC has the same feature...a narrow and WOT setting..and you an set where the cross-over takes place (at what RPM)...thats how the V-AFC is also right?

So..give me an example here...

You set narrow throttle to say -40% right?
And then WOT to say 0% right? So when it "senses" boost...it gives it more fuel.
So its either -40% or 0%...no matter how much boost youre pushing?

But you cant actually tell it how much fuel per PSI can you? Like you cant program 10% throttle = 1 PSI, 20% = 2 PSI, ETC...correct?

It would be cool if you could make the MAP feed into the RPM input (I doubt they are the same voltage or whatever)..and every 1000 RPMs would equal like a pound of boost...then you can set fuel for each PSI.

 

True you can't make settings for 1 psi, 2 psi, whatever... but the deal is, if you set it at -40% at no boost and 0% at max boost, when you're at half boost the AFC is at -20%; at three-quarters boost it's at -10%. The correction is progressive, it doesn't just go to -40% OR 0%, it goes everywhere in between.

By tweaking the "throttle" crossover percents, you adjust where it begins increasing fuel and make it so it is on the narrow throttle band any time it is in vacuum (mine is set 55% / 95%) so all the increase between -40 and 0 is accomplished between 0 boost and max boost; this way when I'm in vacuum, it IS always at -40% which compensates nicely for the 450cc injectors when I'm cruising.

 

Ahh..I gotcha....I didnt know it was progressive. I thought it went from 040% to 0% directly.

Do you have any idea on the RPM voltage?

 

RPM was my first idea but unfortunately the RPM is read from the ignition trigger which isn't so much a voltage as a frequency... it counts how many times per minute the ignition fires; to do what you're saying you would have to convert a DC voltage to an increasing frequency AC signal. This way is much easier,and I think it's useful to have an RPM vs. boost adjustment since the engine has different fuel requirements at a given level of boost at different engine speeds especially with VTEC and secondary runners. Implemented the way you're suggesting would give you a boost vs. throttle position fuel adjustment which doesn't seem like it would be as useful. The ECU already knows how to adjust for throttle position, I figure I can lose that adjustment and replace it with boost.

 

So what are all the components you would need to do this setup?

 

OK...well good deal.

I think the idea is sweet as hell! If I ever decide to get a turbo...Im definately going to use this option. I know of peeople who have blown motors using FMUs whn the vacuum hose blew off and it didnt add fue as needed...with this setup things like that arent and issue. Also the stock fuel pump can be used...and you dont need to worry about running rich at idle...it rocks!

Mna..I could do a turbo setup for WAY cheap...hehehe..maye a turbo is in my future