MAF Functioning Problems

[NismoTypeX]

Hi, I have a 93 240sx. This car runs and Idles really Rich, unplugg the MAF the Car stopps smoking(black) and running rich, so I narrowed it down to the Mass Airflow Sensor. I had a shop look at it and they took apart my wireing harness and installed a new ground wire, for it. what I need to know is on a 93 are the wires that plugg into the sensor: White, black, Black/white, (exactly in that order) I had a guy at my old work (nissan dealership) check it out, he was like *WTF!* (and hes a master Tech). The Computer checked out to be ok. Me and the technition ohmed the wires out (they do connect at both ends) So Im stuck clueless to what has happend, I bought a brand New MAF sensor and it dosen't change nothing. Have you heard of this problem?? I can't drive the car till its fixed. Can you please give me any insight as to what you know, and ask me any questions if you like.

thanks-Sam

[NISTECH]

yes that is the right order.Here is a photo of the wiring harness out of the manual. have you used a volt meter to check the readings coming off the maf? If not do so and post your results.

[NismoTypeX]

The code 12 keeps showing on the computer (MAF) me and the Tech tried to erase the code with a scan tool but yet it won't go away. He mentioned something that it was giving a voltage reading of 5.1volts with engine not running. he mentioned it is way to high and the highest is 4.8 volts at max throtal. Thats all I know on the voltage. And my Automotive Teacher at my school wanted to know if the computer continously gives the ground to the MAF when the key is on. becasue The volt meter said oL. (which means it isn't makeing a conection) That was with a back probe on the black(center wire) and the positive voltmeter wire one the Negetive battery post (I think). Somethin is up with that wire not showing contiuity.

[NISTECH]

the black wire should have .2v or less to ground. if it is open you need to supply a second ground to the intake manifold from that black wire. you have no ground thats why the meter reads 5 volts. The hot wire in side is not "burning". The wire is the load in the circuit if it doent have a ground it will show 5 volts. If you supply this alternate ground your meter will read properly and the car will run a hell of alot better. You will however have a slight rough idle due to the fouled plugs.

[NismoTypeX]

So running a temporary ground wirer to the frame(intake manifold) from the ground side of MAF should not hurt anything? I could care less about rough idle, I just don't want it to smoke in the upper RPM ranges. that would supply a battery volt ground, (this is ok?) and won't mess up my Sensor? (this would only be temporary anway) Thanks

[NISTECH]

you do not want to run it to your battery , you need to run it to the intake manifold where the other grounds are.

[NismoTypeX]

The Nissan Technition at my old job seems to think, that 4-5 wires that provide grounds to the ECU may have a bad connection, possible corroded. And may have cause my ECU to go bad. Basically adding a ground wire to the MAF to intake manifold only solves that one problem, we tested it and It makes the car run better, but runs lean now. So it may be the ground that is provided for the MAf system along with what ever else is in the circuit. this seems to be our conclusion seeing that I swapped ECU's and it dosen't change anything. Do you know if you have a Diagram that I can look at for the ECU grounds? And any tips on how to further test this this? Thanks

[NISTECH]

How do you know its running lean? Did you look at the O2 voltage?

[NismoTypeX]

I know its running lean becasue it was running rough w/out smoke so we enriched it 25% with the hand held computer, the car ran alot smoother a reved harder, and no I havn't checked the 02 sensor, but i'll check it out saturday, any specified voltage on that? and are those able to be cleaned (its probally coated in a thick layer of coke becasue of the excess gas)

[NISTECH]

if you have a hand held scanner you should be able to watch it with that. It should fluctuate between 0 and 1v about 5 times in 10 sec. If the car is runnin lean that reading will be close to 0volts and not go over .5volts at all.