a popular mod for the 89-95 jeep 4.0's ( pre obd2) is an Map Sensor Voltage Adjuster. The reason is the factory ECU doesn't compensate for enough fuel after bolt-ons are added (such as a better intake manifold, Bored Throttle body, or exhaust system). so with this part, adjustments can be made the the map sensor voltage to richen up the fuel mixture, even to the point of stalling the vehicle out (NOT RECOMMENDED ) and can be used as an inexpensive way to tune the A/F's if you use a wideband to set it. How it works is that it adjust the input voltage, which also increases the output voltage back to the ECU. the reverse also applies. Only 1 wire on the factory harness needs to be spliced. the theory behind this is when you raise the input voltage it also will race the output voltage from the sensor itself


They can normally be found in aftermarket parts magazines for around $120-150. But i started making my own and selling them for a way more affordable price. generally the cost to make these ranges from $15-30 depending on what you use. and just about everything can be found inside a RadioShack.


First, a little basic info on the Jeep MAP sensor...
The Manifold Absolute Pressure (MAP) sensor is located on the back of the firewall and it senses the air pressure inside the intake manifold. The intake manifold pressure is converted into a voltage signal that's transmitted to the engine's computer which then determines how much fuel the engine needs. Under low vacuum conditions (WOT, throttle suddenly opened) the MAP is higher, the MAP output voltage is higher, and the injectors are held open for longer to inject more fuel into the cylinders. Under high vacuum conditions (throttle closed, deceleration), the reverse applies.
The MAP sensor is basically a three-wire pressure sensitive variable resistor. The three wires are the 5.0 volt input (purple/white on left), output voltage to ECU (red/green in middle), and the ground wire (black/blue on right).


Supplies That I used:
-Project Housing( the sell plastic project cases at radio shack, but since mine was going to be mounted inside i decided to go with an Aluminum Case made from a fence post)
-Multi-turn Cermet Potentiometer 1000 ohm "trim pot"
-LM317T Adjustable Voltage Regulator
-220 ohm metal film resistor
-Mini Terminal Strip
-Heatsink for Regulator
-SPDT toggle switch
-standard DPDT Automotive Relay
-extra 16-18 gauge wire
-solder/solder gun OR terminal connectors depending on what you want to do(solder preferred)
-heat shrink tubing

Assembly....
i designed mine to only have one toggle switch that will power the unit and switch over from the factory input to the adjusted input. that way if any problems occur, you can switch back over to the factory ECU setting.

here is a wiring diagram i made up for my setup. when the toggle switch is turned to the on position, it activates the DPDT relay. which the relay then turns the MAP adjuster on and switches over from the factory Input to the adjusted input



-make sure to solder and heatshrink all connections
-once all the wiring was done i placed the wiring and relays inside the aluminum tube and secured it with self tapping screws from the bottom, everything is snug and doesnt move.
-also have some vents drilled in to help dissipate any heat created
-i then drilled a whole to give me access to the "Trim Pot" adjusting screw
-when getting ready to install you need to can wire everything up except for the teal wire in the diagram and check to make sure it works with a volt meter.
-dont go over 6.5volts, you risk damaging the ECU.
-and finally after installed i suggest checking the afr's to fine tune it.

I know this is a pretty low budget project, but it is popular with alot of the jeep 4.0 crowd

Picture of the voltage regulator


The Trim Pot and the terminal strip


the basic part of the project setup


Bare Casing


Everything drilled



Everything inside before being secured down


Finished



onlything i dont have a picture of is the harness coming out the back, it should be 4 wires.
-one for a ground
-one for the 12v source
-one for the factory ECU input wire to be connected to
-and one for the output wire going into the map sensor

i think i covered everything

 

would this happen to help with putting a turbo/supercharger on a jeep?

 

its mainly to help more with a bolton motor or a stroker setup. i wouldnt trust it to support any boost since the factory map sensor will not read boost

EDIT: although i did use it on my nitrous motor on my 90' XJ

 

I know this is a year old thread, but i figured i'd ask in an exsisting thread instead of starting a new one. how does this work in perportion to the throttle, does the voltage still increase/decrease with throttle?and can this be used to run a lean mixture as apposed to a richer one? what about setting up the trim pot to be adjustable on the fly? again, sorry for bringin up an old post, just didnt want to bother with a new thread when there's already one here.

 

yes, the voltage will still increase/decrease with throttle.

it controls the pulse width of the injector cycle, so yes it can be used to lean out the mixture as well


and adjusting the trim pot makes instant changes, so you could change it on the fly. i even considered building one with a **** on the trim pot and an LCD voltage display to show the real time voltage numbers. just never had the motivation to follow through with it. but its all possible and easy to setup

 

Then i think 'm picking up a JY map sensor and some electronic parts. thanks dude.

 

Wow I used a hobby box from radio shack and mine turned out like 1/6 the size of the one on here. http://www.angelfire.com/my/fan/MAP_adjuster.html kind of a pain but effective. I totally dig your volt meter idea Btw.

 

Hello, I know this is a super old thread and I'm hopeful your still around and can answer a couple questions. is the toggle switch use a simple SPDT toggle switch on off or on off on? Also, for the resistor what wattage did you uses? Thank you so much for posting this diagram, this is going to help me immensely to get my jeep squared away with my running lean issue! Thanks in advance for your reply!

 

Google "****** GoJeep" and you will be taken to a site where a guy has done brilliant mods to an XJ, including a simpler version of this.

He was a 4wd mechanic and long time XJ owner, his site is one of the best