dbman96

OK I had some sort of epiphany last night... I was looking at my sensor readings on the VAFC; and I'm thinking... would it be possible to hook up the MAP sensor input signal to the throttle input on the VAFC? The MAP voltage at idle vacuum is pretty close to the voltage of the TPS at 0 throttle, and the sensitivity is adjustable on the VAFC for the max level. If I did this, I could use the narrow throttle adjustment to set my fuel at max vacuum, and the wide throttle adjustment to set the fuel correction at max boost, and the VAFC would interpolate between that for all other conditions. Is this crazy or might this be a cheap way to have a decent boost-rpm correction map? I know the only way I could pull it off is to have no check valve on the map and use the J&S map limiter on the map signal after it leaves the VAFC to ensure the ECU never sees boost, but I think this just might work!!! If I can get some time I might try it tonight.

By the way... any hondata users or anyone else know what the approximate max voltage of the stock map sensor is? I know at 20" vacuum it's around 0.4V, atmospheric its just about 2.8V; I'm guessing at around 10 psi it would be close to 5V or a little higher. Anyone know from experience?

Start piling on the constructive criticism!!

dbman96

Can someone at least tell me if this idea has any merit or if I'm completely toys-in-the-attic, truly-gone-fishing crazy?

DIRep972

iTrader: (1)

its way over my head..

Ubermensch

I thought the problem with the MAP sensor wasn't just the computer wouldn't have a fuel map for the pressure, but that it also couldn't physically handle pressures above a psi or two (i.e. sensor would break--I'm guessing its a diaphram pressure sensor). I could be wrong, but I'd be careful.

dbman96

Actually most people running hondata or haltech or whatever on low boost use the stock map sensor - it's supposed to be reasonably accurate up to around 11 psi.

Jared

Wouldn't work because as soon as you went into boost, your Honda ECU would set a code.

VTC_CiViC

I've read it through and I see what you mean dbman, very creative dude, but my question is this.. what'll happen when the stock MAP reads boost (by voltage off the TPS)? CEL as usual right?


[Modified by VTC_CiViC, 6:17 PM 9/27/2001]

dbman96

Yeah, unfortunately this is where it will only work for people with J&S Ultra V.2 like me - the MAP output from the VAFC goes into the J&S, which electronically limits it to under 3 volts; so the VAFC can see the boost and do its thing modifying the fuel flow, but the ECU never sees more than atmospheric pressure. It certainly has some potential flaws and I'm gonna have to mess with it some but I think it's at least worth a try!

VTC_CiViC

yea basically if you could limit the voltage to under 3V max. between the V-AFC and MAP, you'd be set. heh kool stuff here

dbman96

Yeah... I'm gonna have to put on my thinking cap for this one... maybe after the little lady goes to sleep tonight I can go out to the garage and see if this is going to happen or not... (only 3 days back from the honeymoon I'm not going to be spending hours in the garage when she's awake!)

dustin

Sounds like a project

Full-Race Geoff

Very cool idea.

My idea to do this right, is to ignore the TPS and just run 2 map sensors. One to the map sensor on the harness (with check valves or a graddy black box, what i personally love. Then again that j&s should work well too) and run the other map sensor to the TPS location.

let the map sensor at the tps see the boost and block the other.

Very cool idea... let us know how your experimenting turns out!!

-geoff

austrian type-R

this is not an idie, it is a VISION!!!!!!!!!

dbman96

Yeah I had the same idea about running seperate signals from the MAP to both the map input and tps input on the VAFC; I don't think a mechanical check valve like the missing link would work though, because we need the MAP sensor to actually see the boost - we just can't let the ECU see it.

Now that I re-read Z10's post I think his thought is to actually have two seperate MAP sensors... this would of course work perfectly; might be the ideal solution for people without an "electronic check valve" like the J&S.

Anyway... I can't get this figured out while I'm "at work" but I'm definitely going to poke around when I get home... updates will follow!


[Modified by dbman96, 4:28 PM 9/27/2001]

SiRkid

if this works..your a genius

boomslang

Tap the vafc into the map sensor wire before it is limited by the J&S. That way, the vafc will read above 3.0v, and the ecu won't.

dbman96

Exactly.

VTC_CiViC

But assuming you don't have an electronic check valve, how do you stop the ECU from seeing 3V+?

dbman96

The electronic check valve is going to be necessary to pull this off with just the factory map sensor. Alternately, you could put a missing link on the facotry map sensor, and add a second map sensor with no missing link for the sole purpose of supplying a boost signal to the TPS input on the VAFC. I think the first step is to see if it works at all though.

Full-Race Geoff

I dont understand why everyone thinks the missing link is such a cool/novel idea... its really a piece of garbage.

The electronic voltage limiting circuit is really the way to go. Keep us posted on your progress with this...

Accord1999

I was thinking about adding a resistor to the map sensor output to limit the output voltage.

VTC_CiViC

Yea but then the MAP would constantly see too little voltage and think the motor is constantly near idle, even when the TPS signal is open which would lead to a CEL.

Accord1999

Your right, but if carefully done the math and use the right resistor it might work. Have to know the minimum voltage and maximum voltage in the map sensor.

dbman96

Actually a resistor only causes a voltage drop if there's a current flowing through it. ECU sensors have a nearly infinite resistance where they plug into the ECU so any resistor you add to the circuit would have a negligible effect. You could put a huge resistor on the MAP sensor output and it would still indicate almost exactly the same voltage.

zip

Hey, that's actually is a good idea. The MAP voltage outputs you stated are right on. Good luck w/ your endeavor.