Here's the circuit for electronically cutting off the MAP signal at three volts, no more check valves, no more missing link, no more CEL. I'm running it right now on my turbo LS/Vtec, works like a charm. Will sell built circuit on printed circuitboard for $20 shipped. You will have to splice it into MAP circuit. IM me with questions. I'm thinking about adding TPS functionality to the circuit so that one can have control over the throttle position sensor output voltage as well. This would allow you to force open loop operation sooner.

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


[Modified by filetofit, 10:35 PM 7/15/2002]


[Modified by filetofit, 12:23 AM 7/16/2002]

 

is the non inverting input on the bottom, like this?

 

Correct. Also R1 and R2, R3 and R4, R5 and R6 are cermet pots so as to allow for fine tuning. I've got to pull the components off my breadboard and measure the exact values I used and post them.


[Modified by filetofit, 9:50 PM 7/15/2002]

 

okay...obviously I don't know very much about electronics, but why can't you just split the voltage like this?:



I tried this and it wouldn't even run as well with 450's as just having the fpr and nothing else. I also tried just having a single pot:

MAP----/\/\/\-----ECM
******** ^
*********|
--------Ground
ignore asterisks (used for spacing)

this might have worked, but I didn't set it to split the voltage so that 1/3 doesn't make it to the ECM...any thoughts?

Edit: I already orded a couple rail to rail op-amps


[Modified by ion_four, 6:39 AM 7/17/2002]


[Modified by ion_four, 7:09 AM 7/17/2002]
christ, ****** formatting...


[Modified by ion_four, 7:58 AM 7/17/2002]

 

with that circuit, your closed loop performance will greatly be affected. if would have to take a lot of adjusting the pots while driving to even get the voltage split even anywhere good for open loop.

 

I was going to figure out how I needed to have it twiddled to split the voltage, before I put it in, so that would help...so, the honda ecm uses the map even in closed loop mode?

 

The MAP & RPM are critical inputs used to look-up a 'beginning' pulse width. So yes, the MAP is used in closed loop as well.

 

The disadvantage of the twin pot method of adjusting your MAP voltage is that it can only knock the voltage of the MAP output down a fixed percentage. The op amp design provides for adjusting two points, the idle point and the WOT point. You could knock the voltage at idle down by say 50% to idle them and keep WOT equal to 3 volts. In other words with the dual pots you're applying a single scale factor whereas witht he op amps you're adjusting both the slope and the intercept of the MAP voltage output versus pressure curve. It's not as refined as using a VAFC with 8 adjustable points but it's cheaper.

 

could you explain in a little more detail how the two op-amps allow the idle and WOT values to be changed seperately? maybe point me toward a technical resource?

I just got done tweaking my circuit about as well as I could and there certainly seems to be a trade-off between idle quality and WOT a/f ratio...if it idles well; it's lean at WOT and if it idles pretty crappy; it runs well otherwise...sigh...

I already ordered those op-amps, now I just have to understand how they work

 

http://www.intersil.com/data/AN/AN9/AN9757/AN9757.pdf

 

Maybe this will help, the potentiometers alone just allow you to change the rate at which the MAP voltage output changes with pressure, ie the slope of the MAP voltage out versus pressure curve. It also limits you to a decrease in that rate (slope). So in other words if your MAP output at idle is 50% of what it would be normally, your MAP output at WOT will be 50% of what it would be normally. The op amp circuit allows you to increase or decrease the rate at which the MAP voltage output versus pressure changes. But not only that it allows you to add or subtract a constant voltage to the whole curve, moving it up or down a constant amount. This means that you could have you're MAP output at idle be 50% of what it would be normally but 95% or 110% of what it would be at WOT. Why it can do this is a bit hard to explain, hopefully the article will help. Basically it's because you're dealing with active rather than passive electronics.