Anyone try and get better MPG by using resistors on stock xj sensors??

95 xj 4.0 automatic

Just curious, i did move the IAT from the intake manifold to the cold air intake from the from bumper that i built, you think that the colder air is better mpg or just better performance? should i move it back?

Also just using your brain the coolant sensor the colder it is throws more fuel right until motor heats up is there a way to make it think the jeep is already warm?

Also 02 sensor same thing the colder it is the more fuel it throws can a resistor make it lean out?

95cherjustin said:

95 xj 4.0 automatic

Just curious, i did move the IAT from the intake manifold to the cold air intake from the from bumper that i built, you think that the colder air is better mpg or just better performance? should i move it back?

Also just using your brain the coolant sensor the colder it is throws more fuel right until motor heats up is there a way to make it think the jeep is already warm?

Also 02 sensor same thing the colder it is the more fuel it throws can a resistor make it lean out?

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Moving the IAT could richen the mixture, as the intake tube is inherently colder than the aluminum manifold. I did this on my 2.5 YJ, no real proof, but it seemed to help offset the 4.0 t-body and 2.25 exhaust.

People have put resistors on the coolant sensor to make it run richer, but I suppose it could go the other way, but might require more than just a reistor depending on if it is a negative or positive coefficient.

The O2 sensor does not measure temp in any way. When its cold, it is ignored and the PCM uses the learned fuel map until the O2 warms up. You could mess with the O2 to change the fuel mix......

Messing with the sensors is usually not advantageous unless you really know what you are doing. Besides, the O2 reading will probably adjust for any mods you make. You don't want to make the engine run any leaner than it does. Best thing you can do is make sure it is tuned up and running efficient.

If you've been reading the OEM tech section, you'll see how the o2 sensor works:
"An O2 sensor is a galvanic battery that provides the PCM with a voltage signal (0-1 volt) inversely
proportional to the amount of oxygen in the exhaust. In other words, if the oxygen content is low(read rich), the voltage output is high; if the oxygen content is high(read lean) the output voltage is low. The PCM uses this info to adjust injector pulse-width to achieve the 14.7-to-1 air/fuel
ratio necessary for proper engine operation and control emissions."
You want the computer to think it is running rich, so that it will lean it out. Installing a resistor will drop voltage and make the PCM think it is leaner than it is and thus will add more fuel(not what you want, but maybe what someone wants to richen up the AFR). You need a voltage(mV) adder to trick the pcm that it is running rich. Maybe another way would be to fool the o2 with what it assumes is fresh air(I don't want to think more at the moment, so I'll leave it alone right now).

I just found a great article for leaning the map sensor out

http://www.angelfire.com/my/fan/MAP_adjuster.html

Hey i know I have OBD1, is there a port i can hook into on the jeep anywhere that i can then plug into a labtop??

95cherjustin said:

I just found a great article for leaning the map sensor out

http://www.angelfire.com/my/fan/MAP_adjuster.html

Hey i know I have OBD1, is there a port i can hook into on the jeep anywhere that i can then plug into a labtop??

Click to expand...

I did this exact build on my 95 yj mentioned above, it did what it was suppose to, but the O2 will still adjust the fuel mix.

I am going to say it again. Don't lean out the mixture any more than it is. The 4.0 runs lean from the factory, if you lean it out more your are asking for trouble.

Google scan tools. There are alot of write ups and products to interface a laptop to a PCM.

Where is the interface on the jeep i did find a obd1 and obd2 cable website but where do i plug into the jeep its a 95 xj 4.0

any ideas where i can plug into the 95 jeep? thanks

the diagnostic link should be under the hood next to the computer (driver side fender). its a sort of square connector with female spade terminals, i think 5 or 7. if its a very late 95 it may have OBDII which would make it a trapezoid connector under the steering column, but again, im not sure if any 95s had OBDII

Yea i looked all under the dash in my 95 xj cant find any obd connecters i look next to the ecu under the hood on fender drivers side and only connector is an l shaped one any ideas or tunning devices that hook into this thing.