Well in my oppinion this is the best mod for the M42 and works even better with the Mark D ship.
The parts list consists of a MAF, Harness to connecto to the MAF and some kind of electrical device that translates the voltage signal from the MAF to a signal that is similar if not exactly like the the one that cam out of the old AFM.
The stock AFM uses a 5 volt refrence voltage supplied by the DME which it rases and lowers to indicate the load as air moves the flap inside the AFM. Pretty siple device, variable resistor moved by an arm whichis moved by flowing air and is spring loaded to fall back into place and for some other reasons that I am not aware of and are not important to this discussion.
The voltage requirement for the most MAF's is 12V. I chose to use a MAF from a V6 Audi since it has only three wires (simple connection) and more importantly because it was free. There are countless other Mafs out there that can be used and that have been used succesfully. The most popular one would have to be the Ford units such as the 5.0 mustang unit that
bmwman91 has calculated can flow way more that the M42 would possibly suck.
The typical connection for the typical maf would be a 12V supply, ground and the signal which varies from just above 0V to just under 5V. The reason they dont go from exactly 0v to exactly 5v is because the newer DME's use these values to indicate a fault for the OBD systems. If it gets a 5v signal it would indicate a short to "+" and if it gets a 0v signal it reads this as short to ground.
Now the other thing the old AFM does is reads intake air temp with a 5v signal sent through a temp sensor that reduces in resistance as the temp increases, this is how most Bosch temp sensors work. Knowing this I got a temp sensor from a VW Jetta of the 93-98 vintage with the 2.slow engine and also since this part was also free. I made a nut to thread onto the sensor and stuck it in the side of my stock air box.
Now how to hook up the maf, I uesd the stock signal wire that goes from the old AFM and spliced it up to my "new" MAF pigtail to the pin that coresponds to to output signal of the MAF. I used the 12v supply that feeds the injectors and tapped into it in the junction box under the intake manifold and took the last remaining wire from the old AFM and cut it from the crimp joint that is also in the junction box under the intake manifold and put a ring connector on it and gounded it the support leg of the intake manifold.
Of the 5 wires that go to the old AFM 2 are for the intake air temp sensor and the other three are for the air flow sensor. So at this point we have the two IAT wires hooked to our VW IAT. The other three wires are hooked up to the 12v supply and the ground and the fingal one to the input signal to the DME.
Now the fun part is the piggyback unit. There are many units out there so choose wisley or choose the cheapest, what ever rocks your boat.
I purchase a perfect power smt6 because it was cheap and on ebay. I thought about using the apexi safc and did try one but the unit i used did not have a throttle input and it looked too ricey for me. The smt6 is mounted right next to my stock DME and is out of sight. You do have to use a computer to program it and would be nice to use a dyno but I didnt and it runs fine. I purchase a cheap A/F ratio meter off of ebay and used it to get an idea as to how it was running as I tunned it.
Read the instructions for what ever unit you choose and connect accordingly. As for my smt6 I connected between the singal comming from my "new" maf and sent the manipulated signal to the DME. On the smt6 software interface you can manipulate the signal and also if you hooked it up to you O2 sensor you can monitor it in a graphical display that was very usefull as I tunned it.
Any questions?
Topic: MAF conversion (Read 6223 times)