How do i test the MAFS

[elvis240sx]

I searched but didnt see anything on this, so here goes:

I have a sohc 240. I am wondering how, if at all, I can test the MAFS. I do have a digital multimeter and know how to use it, which is what i assume i will need. ANy help would be appreciated, thank you.

[Altiman94]

I was told to tap the unit with your hand or a screwdriver and if your idle changes, it needs to be fixed/replaced. I may be wrong though.

[greasybob]

Go to "http://nicoclub.com/zerothread?id=34234" and read my suggestions to that guy.

If that link doesn't work, look for a thread named "Bogging, no power when warm" under the "Nissan Online Mechanic section and you'll find it. Yours is a 1990 SOHC, but the electrical tests for the MAF will still work. Have at it!

[yellow_jacket]

The MAF should have an output voltage of about .5 volts(most cars anyways) at idle and should gradually increase with rpms. At 3,000 rpms the voltage is usually around 2-3 volts. Then of course you should have your positive and negative leads.

[elvis240sx]

ok i tested the mafs today, and it didnt seem right. i had the volt meter on dc because it just makes sense that way, and used the battery for my ground

there are three wires going into the harness on my sohc. from left to right they are white, black, and black with a white stripe.

the white on the left read 1.5v while the car was idling

the middle black read negative .004

the black with a white stripe was exactly 0, so i assume its the ground

there is one problem that i noticed but never thought was a problem before. the middle wire which is black and had a voltage reading of -.004 was spliced into. The original wire is still intact and hooked into the harness, but another wire is connected to it and hooked onto the engine. I assume this is a ground, since i get very lot volt readings with it.

Im not sure where to go from here. I know i should have one wire that is power from the battery, but i dont. I have a ground so i know that isnt the problem. SHould i disconnect this spliced in wire or would it possibly cause problems? Any help would be appreciated. I can provide pictures tomorrow if i am not being clear.

[greasybob]

The black with white stripe wire should read battery volts. The black wire is ground. The white wire is the MAF output to the ECM. Since your white wire reads 1.5V at idle, I'm guessing that your MAF is getting it's battery volts. Double check that black with white stripe wire again, make sure your probes do make good contact and you use the right scale on your meter. Also, try different locations for your ground reference probe. Maybe you've got a bad ground cable somewhere, (battery to engine, engine to chassis, or ??).

Also, when yellow_jacket says .5V at idle, I think he means .5V with key on, engine not running.

[yellow_jacket]

Could be. I think the last Mazda I had to do was supposed to read .5 at idle. Been a little while though and every car is different.