94 Ranger No MAF Signal

[Psychopete]

I've been poking at this for a few days, I don't have any voltage between MAF RTN and SIG (terminals C & D).

Terminals A & B check out OK - 12v and chassis ground.

I tried another sensor and it's the same thing. My computer is setting 157 CM and KOER, KOEO is 111. Additionally it's setting a 998 during KOER and not completing the test.

MAF SIG D -> RTN is open.
MAF SIG D -> Ground is .517k ohms

MAF RTN C -> Ground is open.

MAF RTN C -> Positive should read 12vdc KOEO, correct? (it's dead there)

Can someone verify that MAF RTN (terminal C) is a computer supplied ground? If so, can I just ground that to chassis and call it a day if that solves it?

I'm more than likely pulling the computer out tomorrow, but would like to avoid that if possible.

 

[RonD]

You will need to test pins 14 and 15 at computer(PCM)

They are the MAF and MAF RTN

Diagrams here

 

[Psychopete]

Wiring checked out good. Took computer apart, burnt up traces and a blown cap.

I replaced the MAS 6 months ago, was getting too high and too low voltage codes. The old MAS I replaced read 24 ohm from 12+ batt (A) to MAF SIG (D). The new MAS it has on it is open between those pins. I think 12v was getting where it shouldn't be and that ultimately fried it.

Now to find a computer =/

 

[RonD]

Well if that 12volts found its way back to MAF pins 14/15 on the computer then that could be what fried computer

MAF voltage is 5volts IN from computer, and then Return voltage is about 1.5volt at idle and gets steadily higher as air flow/RPMs increase, usually tops out around 4.5volts

Image of that here: http://www.aa1car.com/library/maf_waveform.gif

 

[Psychopete]

I replaced the old computer with a reman from Cardone and just got home from a test drive - MAF voltage is back to normal, check engine light is off, and I don't have to drive with two feet to keep it running anymore.

 

[RonD]

Good work

Thanks for the update

 

[Psychopete]

Thanks for the help!