how to: s14 sr20det maf alternative, ka24e maf sohc - Nissan 240SX Forums
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#1 Old 03-24-2009, 10:20 PM
 
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how to: s14 sr20det maf alternative, ka24e maf sohc

mods please sticky this, as any information on doing this mod was straight up impossable to find. everything i did was collected from other mods people did for different reasons.
*purpose: this mod is for using a sohc s13 ka24e maf with a s14 sr20det, and not having it bog and run insanly rich.
*cost: like three bucks at radio shack, plus what ever you pick up your SOHC ka maf.
*what you will need: a sohc ka24e maf off an s13 with clip, a linear taper 50k OHM potentiometer from radio shack, mine is rated at .5w and the part number is 2711716. make sure you use a 50K ohm not a 50 ohm, big difference.
solder, soldering iron, electrical tape, volt meter.
*purpose: ok, the s14 sr20det mafs are rather expensive and almost no swaps come with them. z32 mafs are a better alternative, but require a safc or some other piggyback to run correctly. considering how expensive and restrictive the sr mafs are, i opted for a cheeper and more expendable alternative that i can easly throw in the trash when i decide to upgrade.
i found out some time ago that you can use a sohc s13 maf with the sr, but when i wired everything up the car ran extreamly rich and would not break over 5500 rpms at full throttle, or anywhere close. i had better luck with the combination of an emanage leaned all the way out and the same maf but i've since sold my emanage, baught a s13 and put the motor in there.
*some things to consider: ok the s13 maf output reads around 1.56 to 1.8v at idle after warm up. this is the white wire on the maf plug. the s14 sr20det fsm says it should read around .8v to 1.5v
*procedure: if you are running a brand new harness, you'll need to extend your maf wire, this should have already been part of your swap as it is common knowledge that stock maf wires on sr harnesses will not reach. wire in the clip for the s13, all the colors match up exactly to the s14 sr harness.
*note: when extending your sr harness, use shielded wire like the harness already has, just solder the shield togather
white to white,
black to black, and
black with white stripe to black with white stripe
you need to cut the white wire and place the potentiometer on there and solder in place. here is a nifty diagram to explain everything.

after everything is wired up, take your multimeter and test the ohms resistance between the two parts of the white wire. test on a 200K ohm setting if there is one.
rotate the potentiometer clock wise to make sure it sweaps to somewhere around 50 ohms, then counter clockwise to zero. leave it at zero.
start the car and give it a quick rev to make sure the computer will let it rev past 3000 rpms (if not then you have the wrong maf or the wiring is wrong and the car is in limp mode)
you can also drive it like this, but like i said, it wont break past 5500 rpms under heavy throttle and run rich.
what you need to do next is take your multimeter and test the voltage first comming out of the maf (via white wire), it should read somewhere around 1.5v to 1.8v depending on if the car is warmed up or not. (you should do this with the car warm)
now, take the potentiometer and rotate it clock wise. at the same time test the voltage on the white output wire GOING TO THE ECU. you should see a slow voltage drop as you rotate the nob. shoot for around 1-1.2v starting out and see if that fixes the problem. if it still bogs around 5500 rpms, then rotate a LITTLE more. mine is set around half way and runs perfect.
WARNING! WARNING! WARNING!!!
you now have a very easy way to lean your motor out. i'll admit the s13 maf makes the car run way rich, but you also have the potential to run the motor lean and detonate and blow your sr. this mod is at your own risk and i take no responsability for what you do to your sh#$.
you should be fine so long as you dont max the knob out, i didnt check to see how low it would go, but i'd imagine anything lower then .8v is detonation level.
wrap everything up, the white wire is an exposed power wire and will need electrical tape so it doesnt contact the chassi.
now go for a spin.
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#2 Old 05-31-2009, 06:23 PM
 
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are you completely removing the maf sensor out and replacing it with the potentiometer.. how exactly are you mounting the potentiometer..
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#3 Old 05-31-2009, 08:54 PM
 
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Do the s14 SR maf and the ka24e maf both run up to 5v?
If they do then since you are using a rheostat, your pot steps the idle signal down from 1.55v to 0.8v (factor of 0.51). So your max vaoltage is only ever going to go to around 2.5v
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#4 Old 06-03-2009, 07:59 PM
 
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Decent write up! I personally fucking hate mafs! Im running microtech on a map, but it's nice to see people trying different shit.....

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