'92 Explorer CHECK ENGINE - codes 157 & 158

[R&T Babich]

Hi, to everyone, we're new to this forum.
My wife's '92 Explorer XLT 4x4 with 202,000 miles has been a great car. We've replaced the battery, alt, starter, A/C, P/S pump, muffler, several sets of front brakes/rotors, oil every 2k, filters - all the normal wear and tear stuff. The engine, trans, radiator, hoses, rear axle, front axle, catalytic converter are all original. This is the first time I've had to hook up the code reader (Innova 3143).
The problem we're having is a rough idle and bogging when trying to accelerate from a stop. The CHECK ENGINE light is on. The CHECK ENGINE light had come and gone a couple of times, but is on solid now. When the CHECK ENGINE light was off it would run fine. My wife works 2 miles from home and it hasn't been above 30 mph since this started. We stopped driving the car so I don't know how it performs at speed. Dug out the reader and found the connector. The KOEO test with the reader shows codes: 111, 157 & 158. Codes 157 & 158 seem mutually exclusive. My first thoughts are "Bad MAF" or the wiring harness has a broken wire. The wires hanging from the MAF connector are under more tension than I think they should have, but there is no easy way to support them. I've visually inspected the wiring harness and all looks good. I have 2 other MAFs to try after running VOM tests on the wiring. The Haynes I have seems to describe the procedure well. One of the MAFs shows 3.9 ohms from the SIG pin to the two GND pins. I'll ohm test the MAF on the car (and the other one when I find it) and run the voltage tests this weekend.

 

[R&T Babich]

Update:
Tested the original MAF and there is 3.8 ohms across the SIG and both GND pins so I think the MAF is OK. Checked the voltages:
battery = 12.8 v
KOEO, connector unmated, B+ & PWR GND = 12.0v (terminals A & B - red & black)
KOER, connector mated, SIG & GND = .2v and does not change when rpm increased (terminals C & D - pink/blue stripe & blue), CHECK ENGINE light is on. Turned engine off.

I think the problem is the voltage is incorrect (low) for the SIG line.

I fiddled with the test connectors and reran the test - CHECK ENGINE light is off and running smooth. Voltage across SIG & GND = .5v and increases to 2.3v with an increase in RPM.

Removed the test harness and connected everything up normal. Restarted and after a few seconds rough idle and CHECK ENGINE light is on. Repeated and about every 5th or 6th restart it will run smooth.

If I'm reading the wiring diagrams correctly in the Haynes the SIG and GND lines go to pins 14 & 15 of the EECM. Something is intermittent. The EECM, wiring or the MAF. The Haynes shows the MAF SIG & GND are taps off the circuit from B+ to PWR GND thru resistance (the screen). Could one leg of the SIG circuit be shorting inside the MAF? There may a short in the harness or the EECM may be acting up. I'll try replacing the MAF in morning. Anyone have any experience with this?

 

[Glacier991]

WOW... LOTS OF POSSIBLES HERE... IT MIGHT BE HELPFUL TO KNOW THE CODE THAT IS BEING THROWN AS A STARTING REFERENCE POINT. (OOps caps lock, sorry). Retrieve the code before you do anythign else.

 

[R&T Babich]

Update & problem resolved:
Although the original MAF and a spare I have both read almost identical ohms across the SIG/GND and SIG/PWR GND terminals the problem went away after I replaced the MAF.
Probably unrelated, but while I was checking voltages I found with the engine running the voltage was reading 15.2 volts across the battery. Looked like the regulator was not working properly so I replaced the alternator with a spare and now get 14.2 volts when running. I did this before changing the MAF thinking maybe some reference signal in the EECM might get messed up with the higher voltage, but still got the 111, 157, 158 codes. Anyway, you don't want the voltage running that high as it will shorten the battery life.

 

[r3dn3ck]

do you know exactly what the problem was?
was it the MAF sensor itself?

i'm having the exact same problem.