so if one had a turbo @ 6psi (and cant afford hondata at the moment):

someone who has been there please check my logic here...

get 370cc injectors.

lower fuel pressure to about 30-35psi

drive the car without turbo for a few weeks and verify fuel trims are not deviating more than a few percent. adjust fuel pressure accordingly.

once N/A fueling is spot on, then install turbo.

add FMU at 6:1 rise rate (a little rich)

design circuit that inputs IAT,MAP sensor voltage and RPM signal

circuit will limit map voltage to approx 3v and vary it slightly to modulate injector pulsewidth.

circuit will have programmable fuel map to set injector pulsewidth (map will be a table, RPM vs boost pressure, from map sensor)

circuit will take value from table and compensate it slightly for IAT rise or fall.

hmm, might send fixed IAT voltage to ECU in boost to prevent it from compensating also..

- will this work? or will the fuel trims get messed up? or something else? will messing with the MAP voltage cause the fuel trims to deviate?

- is the IAT messing with the MAP voltage necessary? i think it is...i dont want the car leaning out in the winter...

- should i also modify the TPS voltage so the ECU definitely goes into open loop, if i am in boost at part throttle?

- does the ECU use its onboard atmospheric map sensor to adjust injector pulsewidth? for example would my AFC go out of tune if i drove up the side of a mountain?

 

come on....all you AFC people. will this work or will i turn around and junk this and sell my 370s and have to get 440s and go hondata when it doesnt work?

 

 

Well, if your a EE and you have a lot of time on your hands you could get it to work. Sounds like a cross between a Hondata and AFC hack.

I'm guessing you have a scan tool to read the STFT and LTFT?

I'd say you are going to be hard pressed to get the fuel trim "spot on" just by lowering the pressure. The numbers say it should work but I did not have much luck with 310's and altering the FP. I go bad dead spots out of boost. But I would say that doing this step while still NA is a good idea.

Is your circuit going to have a whole table for possible msnifold pressures at any given RPM ala Hondata? What would you use to build this circuit? A Stamp II or something? The thing you'd have to figure out is how much to lower the MAP signal to shorten the pulsewidth a given amount. Remember, your just moving the stock fuel map down when you lower the MAP signal, your not directly cutting the pulsewidth. If you're going to have this table and limit the MAP at ~3V then what happens to the table after that?

The IAT is used as a multiplier to the stock fuel map. At a given RPM and manifold pressure there is a set pulsewidth. Then the IAT adds or subtracts pulsewidth when the intake temperature is cold or hot respectively. It does nothing to the voltage output of the MAP sensor. The Jackson Racing IAT relay substitutes a false 0 degree reading to the ECU whenever in boost which makes the pulsewidth longer and also adds a bit of timing. I think playing with that, the MAP and the baro sensor would be too much to handle at first.

not sure how the baro sensor comes into play but I know that guys that have done the AFC hack where you replace the TPS output with the MAP output have trouble when the altitude changes.

You'd either have to have two different maps (low throttle and high throttle) or you may just want to kick the ECU into open loop in boost by substituting a WOT TPS sensor output.

A note about fuel trim: The trims only get changed in closed loop. You can play with the fuel all you want in open loop, the ECU will not "learn" anything while in open loop. The only way you're going to affect the open loop trim is by being overly rich or lean in closed loop, the ECU learns that it constantly needs to be leaning out the mix to stay stoich and it carries that over into open loop.

I think you're taking on a bit much but it's a hobby I guess.

HTH

 

yes this is something between hondata and AFC. i think the stamp 2 is too slow for this. i want fast updates of the MAP voltage. it would definitely be somewhere between a hobby project and a real job, but i do this at work (on a larger scale) so i am dumb enough to try it. i am thinking of going with a motorola 68000 series microcontroller...

if i cant get the 370s to behave just like stock injectors, then this exercise is useless, cause the fuel trim values would definitely throw my tune out of whack. this thing would only modify map voltage when in boost. it would leave NA operation up to the ECU.

after what? after you climb into boost? then the 6:1 fmu adds fuel, and the fuel table (RPMvs boost) adjusts the fuel curve so that i get a nice flat a/f ratio.

as far as the IAT...i guess i could see how the car drives and add it if the fuel table needs adjusting over seasonal changes.

as far as the baro sensor, i am thinking that the ecu will throw a code of the MAP sensor sends a signal that is, say, 10% over whatever the baro sensor indicates. since 370s with 6:1 fmu should always be more than enough fuel, i wuld never need to modify the map sensor over ambient pressure, so hopefully this wouldnt be an issue.

thats why the fuel pressure and NA tune must be 'spot on' otherwise this and VAFC setups wont stay tuned.

 

The new J&S has an AFC built in.

I added a D/A converter to the uP, then expanded the V2's MAP Limiter circuit to accept signals either from the stock MAP sensor, or from the D/A.

It's not user programmable, but it can be pre-programmed for different injectors. Three mode switches will be used to either select the injector size or tweak the table. Need data from S-AFC users.