schwett

correct, it's only for hiding boost. i wouldn't trust actual fuel management to anything homemade.

the tl431 is basically an adjustable voltage regulator. the value of the resistors determines the output voltage. there are probably comparable parts in almost everyone's lineup, the one i actually used is an nte999 that i got at fry's electronics.

Slater

Have you had a chance to play with the actual voltage yet (during actual use) to see what the limit actually needs to be set at?

The Helms manual says the MAP tops out at "approx. 3v".

Hondata's says "w/ the ignition switch on but the engine not running the standard MAP sensor should read 2.85V between the MAP signal and GND wires."

Is every MAP gonna be a little different, and if so you would have to set each car up with the pot? Or is it safe to say that ALL Honda MAPS should be electronically clamped at 2.85 or 2.86 or 2.84 or whatever voltage?

Thanks for the great gadget!
- Slater

ion_four

The ecu should be standard. The MAP sensor might put out 2.85v at 0psi, or at 1psi, or -.01psi, but it's still 2.85v at some point, so the ecu will freak then. I was talking to a guy I know with a Dodge Omni turbo and he just put a Zener diode in series with the map so that it cut it off at a certain voltage. It apparently works well. I did find one on the internet that cuts at 2.8v. would this work?

EE_Chris

The ECU typically sets a MAP code when its value has EXCEEDED the Baro sensor value. So its basically altitude dependent. Yes, its around 2.8V with a KOEO situation....but thats sea level. Do I know what the voltage would be at what altitude....no I do not. But to nail it down to 2.85V is a little inaccurate.

Would it not be worth a try to use the Baro sensor wire as the control voltage for the shunt regulator? That way your gaurunteed the MAP will never go above the Baro....well, in theroy, right.

Your relay idea looks good to. The only thing I would add, is a diode, reverse biased, across the relay coil. When a coil de-energizes, the field colapses and induces a negative voltage that back feeds into the main power wire. A 1N4001 or something in that series should work fine.

CovertFI

a zener diode should work!! that is a good idea

94turboteg2

Good point about the baro sensor, where is this located anyway?

schwett

i was thinking about this, but unfortunately, on my car, the baro sensor must be *IN* the ECU.... or there isn't one.

Slater

The Air Pressure Sensor in the lower right hand corner of pic:



- Slater

schwett

thanks for that... i'll open up my ECU someday when i'm feeling ambitious.

i wired the device in last night; so far so good. i blew into the map sensor tube and the ECU did not freak out, but it takes longer than a few minutes of boost sometimes.

ion_four

Alright; I think I've decided to go lo-tek electronically with my engine managment scheme (mostly because I'm not that good with electronics)...I'm still waiting on my goddamned 450cc injectors, I think the punk ripped me off, so I haven't been able to do anything yet...
I'm thinking two things:
Use a diode to limit the MAP output at about 2.8v (is that too low?)
And then use a resistor combination on the MAP, as well, to lower the output so I can run larger injectors...I'm thinking this is similar to the Greddy Blue box, but I haven't been able to get my hands on one, so I can't be sure...
any thoughts?

Hybrid

So what, with resistors hooked up to the map sensor you can run larger injectors? From idle right on up to party time?

Has there been any development on this project? Both the map sensor voltage limiter, and the resitors on he map sensor

filetofit

I built one, works great, see the webpage below for circuit or I'll send you a built circuitboard for $20.

http://www.angelfire.com/ab7/diymaplimiter/