bypassing MAF with a resistor - Nissan 240SX Forums
S13 240SX (89-94) Technical Questions Specifically for ALL S13's. (Including 180SX's, 200SX's & Silvia's)

 
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#1 Old 11-04-2004, 11:29 PM
 
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bypassing MAF with a resistor

ok I don't have a MAF yet and i know it operates on how much resistance is sent back to the CPU or something like that. So does anyone know which wires I need to connect to a resistor into fooling the cpu that the air is at some constant temp. this is temporary for like 2 weeks, so ill use 93 octane just to be on the safe side. oh and its a 91 KA24DE
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#2 Old 11-05-2004, 12:24 AM
 
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Quote:
Originally Posted by avel_k
ok I don't have a MAF yet and i know it operates on how much resistance is sent back to the CPU or something like that. So does anyone know which wires I need to connect to a resistor into fooling the cpu that the air is at some constant temp. this is temporary for like 2 weeks, so ill use 93 octane just to be on the safe side. oh and its a 91 KA24DE
well there is the power wire, the ground wire.. and there are two more wires... if you have the factory service manual u could probably find out in a snap.

sorry i couldnt help much but if there's 4 wires, id know to eliminate 1 of the two..

and plus it might not work that well even if u find the wire.

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#3 Old 11-05-2004, 01:13 AM
 
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that won't work at all. the MAF is not a temp sensor. it is a flow meter. you have to have a variable resistence in that circuit. a variable resisitence that coincides with the tps as well. you can't just tie in a resisitor and expect it to work, because the ecu will think that there is a constant flow of air coming it. i doubt if it will even start like that.

something wicked this way comes...
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#4 Old 11-05-2004, 01:40 AM
 
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hence why i said i dont thikn it will work.. the power in the wire regulates to send the ecu different signals and the ecu does the math between the TPS and the MAFs... so im pretty sure it wouldnt work at all... you'd just be telling the computer that "not a lot of air is coming in... and the throttle is wide open"

so the computer would go to limp mode and probably just throw codes.

this type of shit mostly works on american cars. there arent THAT many japs that make use of resistors

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#5 Old 11-05-2004, 02:47 AM
 
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Some MAF sensors have an air temperature sensor integrated in as well. My buddy's Supra is like that. We removed his MAF sensor when he installed a MAP ecu, but had to jump some wires at the MAF sensor connector so the stock computer still got a signal for air temperature. Technically if you wanted to fool the PCM about air temp (assuming the MAF in our cars has a temp sensor) you'd just jump the +12 volt wire to the air temp signal wire using a resistor of the correct ohm value. However, the stock PCM must have a reading for the amount (mass) of air coming in, and the only way to do that is to have a MAF sensor hooked up. Otherwise it will not run. If you are lucky enough to get the right ohm value resistor in there for the MAF reading and the car start, that ohm level will be completely wrong for other load and engine speed conditions throughout the rev range.

Basically, the resistor trick can work on fooling the ecu about air temperature but it will not work for fooling the ecu on MAF readings.
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#6 Old 11-05-2004, 07:49 PM
 
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Thanks for the input, you guys kinda read my mind. I'll just get a MAF.
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#7 Old 11-05-2004, 11:24 PM
 
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a hotwire (the MAF that most nissans use)MAF puts out a voltage from 0-5V depending on that MAFs flow %. 0V = 0% air flow 5V=100% airflow. resistance means nothing.

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#8 Old 11-06-2004, 09:34 AM
 
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Basically the MAF takes the +12 volt wire coming in, and the ground wire coming in, and varies the resistance between the two depending on how much air is flowing and sending that on the ouput wire. So resistance means everything. What the guy here is trying to do is put a resistor on the +12 wire and connecting it to the signal wire to make it read somewhere less than +5 volts. The only problem is like you said, the voltage should vary from 0 to +5 or so.

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