'94 Ford Ranger Failure Mode

I have a 94 Ranger... Of course.. The check engine light would come on and go off every so often.. Now it stays on and idles high then low.. Sometimes it will completley stall out when driving.. I have a code reader and the only code I pulled was 157 and 158 in the continuous memory for the MAF sensor and then code 998 which is the code for FAILURE MODE.. In the book it said to check the power steering with turning the steering wheel a half turn.. Did it nothing out of the ordinary. Then it said to push the brakes to floor and then let off.. Did that and nothing happened.. I'm stuck because I don't know how or why the truck is in failure mode. I'm not a tech. and have researched beyond belief to find nothing.. Somebody point me in a direction please.. Thanks in advance.. Dusty

Codes 157 and 158 pertains to the Mass Airflow Sensor (MAF) whereby something is causing it (or is defective) to change the resistance value of the "hot wire". simply, the "hot wire" inside the MAF housing changes resistance as it changes temperature depending on the amount of air intake. The changes in temperature translates into changes in the hot wire resistance which in turn sends a signal to the Power Control Module (PCM) to provide the correct fuel/air ratio.

I suggest two things before replacing your MAF. Make sure your air filter is clean. secondly, inspect the MAF to make sure that the sensing element is clean. If there is any buildup, spray it with an "electronic parts cleaner". Of course do these procedures with your engine stopped and fairly cool to touch. See if it makes any difference.
I got a 99 Ranger and also have an engine check situation code PO171 and PO174 which is associated with system adaptive fuel lean.

Don

I will try to do these things in a few minutes.. They do make MAF sensor cleaner I saw it the other day at NAPA.. I will go pick up a can and see where I get.. I'll see what happens and go from there.. I'll be posting how my luck went.. Thank you.. Dustin

Ok.. I attempted the cleaning of the MAF sensor... It was dirty I could see it.. It did come clean and I put everything back together to find that the check engine light is still coming on and now I get an error code of just 157 which is the MAF sensor putting out below minimum voltage.. I was getting code 157 and 158 (above maximum voltage).. So I am assuming that the sensor itself is shot!?!? Would I be right on this guesstimation??
Thank you.
Dustin

Dustin:

Starting to look like a bad sensor but before you get to that conclusion (just to narrow down options) test for power to the MAF and check for open circuit at the sensor. These tests will require some test equipment (multimeter, etc) and also circuit diagram which you may find in a repair manual. By the way have you tried disconnecting the MAF sensor connector and did it make any difference with or without it hooked up? If things continue to drive you up the wall, might be worthwhile to invest in a professional diagnosic which will determine for sure what the problem is. Then you can decide on your next course of action.

In my case I'm suspecting problems with the O2 sensors. My truck (99 Ranger 4.0L) has three of them and I have to find out which one or two or all are malfunctioning. By the way Pep Boys want 90 bucks to do the diagnostic.

Don

Don,

I did unplugging the MAF before and it did seem to help for a few moments and then the idle dropped which I would believe is what it is supposed to do.. I thought about the 02 sensor/s in my case also.. The truck does smell likes it's burning rich.. With your truck being obdII advance auto can hook it up to the computer and print the problems out for you for free if thats what you mean by diagnostic test.. I have the Haynes manual for the truck I'll look that up.. It just leans me more towards the MAF sensor due to the cleaning and then one error instead of two.. I don't know.. I'll check this stuff out this weekend and see what I come up with.. Thank you for all of your help.. Months of online research and I've got more information from one person.. Thanks again...

Dustin