i found this a while back an figure i should post it up.
this would be good for u guys running the speed density system,w mods.
doing this will allow u to dial in some extra fuel if needed to keep up with any mods u have done.and the best part is no need for computer tunning to do it,or larger injectors.
i see this working well on mods like headers/ex systems,ported heads/intakes etc






Click here for the map mod writeup -- offsite

If anybody does this mod, keep in mind that the baseline reading is taken at key on, so make sure you leave the switch turned off until the car is started or nothing will happen.

also keep in mind that the WOT PW is set in the computer and no amount of voltage changing on the MAP circuit will change the amount of fuel you get when the ECM thinks that you're at WOT.

All this will do is adjust the MAP signal so the computer dumps more fuel at part throttle, where the O2 would adjust anyway, and make the ECM think that you are under a heavier load sooner than you actually are.

even at wot wouldnt the ecm still see a higher load?,im not used to dealing with an sd setup,i know with my maf setup it only runs the proper afr under wot thouhg my situation is alot diff.could also use this to lean the motor out a lil bit for slightly better gas milage as well

Nope. 4.5V is a full load to the ECM, anything over that is still full load it doesn't matter. If you go too high for a certain RPM and TPS Voltage you'll get a code telling you that there is something wrong with the MAP ckt because it doesn't match pre-programmed calibrations for those parameters.

The only thing this kind of ckt mod does is make the computer think that you are at a generally higher load than you are and most of the time the ECM will pick it up as an incorrect value, set a code, turn on the light and ignore MAP signal voltage and substitute something anyway.

When you're cruising, the O2 will pickup lean or rich conditions and fix it anyway. You won't get any better fuel milage from leaning it out because the O2 will see lean and add fuel until it reaches the fuel trim(block learn) limit, then set a code.

This is like the resistor in the IAT or ECT connector. Same idea. All junk.

ahh ok makes sence,though i was under the impression that the 02 is pretty much ignored under part throttle conditions,and really only used under wot

Before people knew who to modify the eprom, people use to do a similar thing with the MAT and/or CTS. In place of the MAT and/or CTS they would replace it with a rheostat. The ECM would see the resistance of the rheostat instead and add/subtract fuel accordingly.

This would solve the WOT issue the MAT.

But to make it work properly, you really need to have a WB hooked up to dial in the right AF Ratio.

I built a similar adjuster before I started Prom Tuning. Ran a 350 TBI setup on a 305 with a cam in it just fine. Had a GM VAFPR and the MAP adjuster.

PS- The WOT pulsewidth is not pre-programmed into the PROM. It comes from the VE lookup table. The MAP plays more of a part than you think it does. The MAP also adjusts the fueling/timing for BARO compensation. The lookup tables end at 100 KPA, which is 4.6 volts.

I was simplifying it...I see that what i said was a little misleading. Sorry, what I was trying to say is that 4.6v is max load, if you give it 4.8v with the adjustment...it'll use the highest programmed PW and that's as far as it goes.

That's 100% backward. Under part throttle/cruise conditions the O2 makes the adjustments to keep the A/F ratio switching between rich and lean for proper catalytic convertor operation. THe Block Learn system also uses this information to compensate for minor rich or lean conditions caused by injector leakage or vacuum leakage. It also compensates for things such as varied sensor voltage that is used in part to determine fuel delivery