I'm still troubleshooting my rough engine idle on my 1994 2.3l and decided to retest a few things.
The MAF seems to make little difference in idle when disconnected
The MAF Sensor is failing Test 3 " Making Sure The MAF Sensor Is Getting Ground (PCM)"
I'm getting a very constant 6.3v between the TAN/LT BLU wire of the MAF and battery +, test calls for 10-12v
Test 4 seemed to pass with 1v at idle and 2v at RPM, If these voltages are in fact correct
I have the PCM pin out chart and will test the TAN/LT BLU MAF ground wire from the MAF to PIN 15 of the PCM
https://easyautodiagnostics.com/ford...ector-pinout-1

Here's my questions .......
1. I am uncertain where to pin out the PCM ground. Is it case ground PIN 20, or Power Grounds PINs 40 and 60.
2. Where do the grounds physically land
3. Am I missing something here, the test 3 voltage was very steady, not like a dirty ground

Thanks!

 

The older MAF sensors have 4 wires, pre-1998 on Rangers usually
2 wires are for the internal Heater, 12volt wire key on and a Ground wire, no connection to the PCM(engine computer)
On a 1994 this should be a Red 12v wire and a Black ground wire(or black/white), with connector unplugged and key on you should see 12volt between these two wires, if so they are OK

Other 2 wires are the sensor part, its a 5volt sensor, these are connected to the PCM
Blue/red wire(pin 14) and a tan/blue wire(pin 15) usually
with key on engine off and 4 wire connector unplugged, one of these wires should test as 5volts to any ground, 4.8v to 5.2volt is fine, blue/red usually, but can be either, even -5volts(negative 5 volts)
If so plug back in the 4 wire connector and start the engine
Test the voltage between the blue/red and tan/blue, .5v to 1.5volts is OK at idle, it goes up when you REV the engine, but really really depends on engine temp and OUTSIDE air "weight"


MAF sensors WEIGH the incoming air, MASS air flow, Mass = weight
The PCM is programmed for the size of the engine, a 2.3liter engine in this case, so the computer already knows EXACTLY how much air is coming in at ANY RPM, its just Math
What it doesn't know is the weight of that air
And air weight changes A LOT
Cold air is heavy, hot air is light, its how "hot air balloons" can fly
Air at sea level is heavier than air in Denver, 5,000ft elevation

So why does air weight matter?
14.7/1 is the air/fuel ratio for gasoline, and its a WEIGHT RATIO, not volume, computer knows the "liters of air" coming in but not the weight of each liter
14.7 pounds of air to 1 pound of gasoline
14.7 grams of air to 1 gram of gasoline

Its why Fuel Injectors are rated in "pounds per hour" of fuel flow

Some computers run fine with MAF unplugged(but stay in OPEN loop), others will stall, this is TOTALLY a software thing in the computer, it can be specific to year/engine software, but its for sure not an "all stall with no MAF" or "none stall with no MAF"
So unplugging a MAF sensor just tells you what software you have, that's all, its not a test if MAF is working or not
But engine should always drive better with a working MAF and proper air/fuel mix of course

 

Ron,
Thanks for detailed explanation!
I was testing the MAF per the instructions here: https://easyautodiagnostics.com/ford...nostic-tests-1
I used the PCM pinout here: https://easyautodiagnostics.com/ford...ector-pinout-1
I'll recheck for the 5v ref and the operating voltage tomorrow

 

I rechecked the voltage and have 5.7v on the tan/blue koeo.
The running voltages running are 1v at idle and 2 volts at RPM
There may be a slight improvement in idle when the MAF is connected.
I'm calling the MAF good for now.

One last question, My O2 sensor looks original, what brands do you recommend?
Given that they're life limited I feel good about swapping it out.

Thanks!

 

Bosch is what Ford used, and I have no complaints about that brand
All Rangers up to 2011 used the same type of O2 sensor, narrow band, and at all locations, only difference is the length of attached cable, so one part number may have a 6" lead and another a 2ft lead, so that's the only difference in these O2s

 

Thanks Ron!!!

 

O2 sensor replaced, It seems to run a little better going down the road.
The closed loop idle is still low and slightly rough, at the tail pipe it sounds like a misfire.
Overall performance is solid, milage is around 19

I'm about to call it quits, I've owned the truck for 17 years, both of my kids learned to drive in it
I rarely drive it these days and It isn't worth much. I don't mind wrenching on it from time to time,
Its already going to need tires, timing belt, and serpentine belt, I dont think I want to put the cash in it