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I have watched several videos, but none of them are about 4-wire MAF sensors or bench testing a MAF. I have a 1994 ford ranger, 4.0L 4x4, with automatic. First I change the MAF sensor because had no power and it fixed the problem. Then had high RPM after a cold spell, I then changed the IAC, which didn't help. I then changed the temp sensor which calmed down the high idle. Then it started to have a miss fire, so I checked /tested the ignition coil and changed the spark plugs. Because of the mileage and using injector cleaners, I got codes 172 &176, So I changed the O2 sensors. Now it starts, RPM’s up to about 1700, and then dies. I unplugged the MAF sensor and the truck will start and run. Plug the MAF in and it Dies instantly. Now I have code 57 – PNP and I also got code 998 which did not pass the KOEO test.
MAF sensor testing starts at 6 min in the video and I think the truck is not California emission, hence the MAF signal pin at the ECM is at pin 14. If your VECI (Vehicle Emission Control Information) sticker says California then MAF signal wire's at pin 50.
The 57 - PNP might be referring to the park neutral switch. Do you have any problem with the truck not cranking?
The code 998 means an out-of-ranger sensor and computer has substituted a fixed value to enable vehicle to continue operation. This is probably because you unplugged the MAF sensor but I'm not sure maybe someone more knowledable can chip in.
