If you are running a MAF based engine such as the SR20DET, RB20, RB25, and 2JZGTE, often times you are faced with the problem of MAF overrun. Mass Air Flow Sensor Overrun is when the MAF simply cannot keep up with the airflow that the engine and turbo are demanding, and can be dangerous if not corrected.
Modifying your MAF isn’t recommended, but it can get the job done
While the MAF based system provides pleasantries of tuning part throttle and gas mileage, it can also lead to frustration when it’s time to turn up the boost. If you are adding a MAF to an existing engine platform, you will need the matching ECU that can accept a 0-5 volt range.
Q45 on the left, RB25 MAF on the right
This will allow your ECU to operate your motor whether or not it depends on MAF or MAP signals to orchestrate the fuel and spark in your engine.
Which is why we’ll be swapping in the ever popular Q45 MAF into our RB25DET swapped 1993 Nissan 240SX today and showing you how to correctly install and wire this unit.
At 90 millimeters in diameter the Q45 MAF ( part number22680 61U00) can readily be sourced from a VH45DE the Infiniti Q45 and is one of the largest OEM hot-wire MAFs money can buy.
It’s best to purchase one with the pigtail, although it will complicate what otherwise is a very simple wiring job. There are 3 pins on the Q45 MAF labeled for ease of wiring installation into whatever engine harness you are working on.
Remove the metal clip that secures your Q45 MAF plug in place. You should now be able to unplug your MAF.
The pins B, D and E are colored blue, green and red respectively. The B pin or blue wire is the 0-5 volt signal that the MAF sends to the ECU, while the D or the green wire is ground, and lastly the E or red wire is a switched power.
You may or may not have wires that are different, all this means is that your plug is sourced from overseas or perhaps came from a similar vehicle that shared the same motor.
Open up your harness and pull out the wires you will need, the signal of course being part of the twisted pair that is shielded.
White wire is MAF signal, part of the twisted wire loom
Now turn to your stock KA or stock RB25 MAF plug, and find the wires you will need from there.
The wire on the furthest right is black with white stripe, this is switched power and must be wired to your E plug on your Q45 MAF. The next wire is your white signal wire, which must be wired to the B wire on your Q45 MAF. And last but not least is the ground wire, which is the black wire going to the middle D plug. The extra wire is not used in this how to install a Q45 MAF guide.
Incorrectly wiring this unit can cause your vehicle to run roughly and will be immediately noticeable. However, problems with your MAF Sensor can vary from inoperating components to sensor failure, especially in a used unit. It can can trigger P0102 OBDII codes if your vehicle is equipped with such. Related OBDII codes are P0100, P0101, P0103, and P0104.
Make sure to check each wire coming from your engine harness. There’s only 3.
Problems with your MAF can be resolved by testing the unit using a voltmeter, depending on the MAF in question testing the resistance range of the filament it not difficult at all. If the MAF resistance range checks out okay, there is something wrong with the board inside your Q45 MAF causing it to not receive power.
When you are running an upgraded fuel pump with larger injectors, this larger MAF will allow your piggyback ECU more range to operate as the MAF is now large enough to handle the boost you can throw at it.
This MAF is directional
We have seen modifications you can perform to your MAF in order to fool it into thinking there is less air than what is really passing through the MAF, but this is not a safe practice. Learning how to install a Q45 MAF is essential if you are intending on passing emissions or running the stock ecu, is one of the easiest and safest methods to upgrade your vehicle.
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