95 Windstar 3.8 MAF Sensor

I need some opinions on what I think is a faulty MAF sensor. I've been getting lean codes, first bank one, now it's both banks. I've been all over it looking for vacuum leaks and just can't find one. A skilled tech told me to get my scanner and go into the live data portion. Look at the short term fuel loop percentage. He said at idle it should be in the positive range, at 1500 or so rpm if it falls into the negative range, that's an indication of a vacuum leak. Well it'll start out in the positive range at start up idling but falls into the negative without even raising rpms. That would certainly indicate a vacuum leak I assume. BUT, I also went down into the MAF section of my scanner, it's reading all zeros. I have some other voltage checks I need to perform from the harness in the morning to verify. I was at a friends house today going over it looking for the vacuum leak. We plugged the scanner in on his 2001 Ford van and a 2003 Toyota truck. They both read 10.115 lb/min in that same section. I am just wondering if a bad MAF sensor could cause the lean codes.

I went out earlier with my voltmeter and checked the voltage coming in to the MAF sensor harness, it was right about 12 volts. My haynes manual says to start the vehicle and back probe the MAF signal+ and GND- terminals. The voltage should be between 0.5 to 0.7 volts at idle, I am getting no voltage at all. So, it's looking like a faulty MAF sensor, I also checked for continuity between the same 2 terminals with the harness unplugged and it ohmed out. So the circuit isn't open, but it certainly isn't sending the signal to the PCM.

Be anxious to hear what your fix ends up being and if it comes down to a voltage stability problem. :) It may help my neverending thread.

Well, I picked up the remanufactured MAF sensor from Advance auto yesterday and installed it. Same thing, no voltage out, I can however take the ground probe out of the harness and stick it on the battery ground post and it shows voltage. It's not within the parameters listed in the haynes manual, but it's voltage nonetheless. I got to thinking that maybe it was a bad ground so I unplugged the harness and checked for continuity all the way back to the ground post on the battery, it ohmed out, so it's a true ground. I also checked all the other wires in the harness at the plug and they check good. So, I guess i've either got a defective MAF sensor or there's a problem somewhere else.:banghead:

My wiring diagrams for the '95 3.8L engine controls are showing the MAF as having four wires connected:

Black/white: vehicle ground
Red: 12V (via the switched contacts of the PCM power relay)

Tan/light blue: MAF Signal Return (that's not the same as vehicle ground)
Light blue/red: MAF Sensor Input (to PCM)

Are those colours the same as your connector, and if so then which two wires are you measuring across?

My wiring diagrams for the '95 3.8L engine controls are showing the MAF as having four wires connected:

Black/white: vehicle ground
Red: 12V (via the switched contacts of the PCM power relay)

Tan/light blue: MAF Signal Return (that's not the same as vehicle ground)
Light blue/red: MAF Sensor Input (to PCM)

Are those colours the same as your connector, and if so then which two wires are you measuring across?
The tan/light blue which is the signal voltage out to the PCM and the black/ white wire (ground) is where I am measuring. The light blue/red wire is the PCM power ground wire according to my haynes manual.

Here is the diagram from the Haynes manual showing the MAF sensor harness.

Hmmm, there's a discrepancy between the two diagrams so I wonder which is correct - I suspect that mine might be accurate because a black/white ground wire seems more likely than a light blue/red. The MAF sensor is at the bottom of diagram 4:

'95 3.8L Engine controls - diagram 1 (http://selectron.webs.com/1995-windstar-pcm-01.pdf)
'95 3.8L Engine controls - diagram 2 (http://selectron.webs.com/1995-windstar-pcm-02.pdf)
'95 3.8L Engine controls - diagram 3 (http://selectron.webs.com/1995-windstar-pcm-03.pdf)
'95 3.8L Engine controls - diagram 4 (http://selectron.webs.com/1995-windstar-pcm-04.pdf)

Electrically speaking, the MAF sensor appears on the diagram as a simple voltage divider with a fixed tap and a variable tap. First thing I'd check is that 12V is available when probing across the black/white and red wires - if it isn't then the rest of the sensor can't function.

Then with the meter's black probe on the black/white wire, there should be some voltage when probing the tan/light blue wire with the red probe, and then a somewhat increased voltage when probing the light blue/red wire, again with the red probe.

You can also measure the MAF sensor's variable output signal directly across the tan/light blue wire (black probe) and the light blue/red wire (red probe) - if the engine is at a steady idle then it won't be varying much, but some voltage should be detected.

A digital voltmeter has an extremely high input impedance so making those measurements won't cause any harm, but if you're probing adjacent wires on the connector, then either put some sleeving on the meter probes or wrap a little insulating tape around them so that only the probe tips are left exposed - that greatly reduces the risk of causing an inadvertent short-circuit if the probes should touch while they're hooked into the circuit.

Electrically speaking, the MAF sensor appears on the diagram as a simple voltage divider with a fixed tap and a variable tap. First thing I'd check is that 12V is available when probing across the black/white and red wires - if it isn't then the rest of the sensor can't function.
We're good here, I have voltage coming in.

Then with the meter's black probe on the black/white wire, there should be some voltage when probing the tan/light blue wire with the red probe, and then a somewhat increased voltage when probing the light blue/red wire, again with the red probe.Doing this, I have no voltage BUT, I can leave the red probe on the tan/light blue wire and then take the black probe out from the ground wire in the MAF harness and put it on the ground post on the battery and read voltage. The Haynes manual says to check for voltage with the car at idle with the black probe on the Black/white wire and the red probe on the tan/light blue wire and it should be 0.5 to 0.7 volts, I'm getting nothing there, no voltage. With the black probe on the black/white wire and the red probe on the light blue/red wire at idle I am showing 1.09 volts.

You can also measure the MAF sensor's variable output signal directly across the tan/light blue wire (black probe) and the light blue/red wire (red probe) - if the engine is at a steady idle then it won't be varying much, but some voltage should be detected.Doing this I get about the same voltage, 1.09 volts.

I think there's a problem with the black/white ground wire - I know you've already ohmed it out but could you check the voltage between the battery negative terminal (black probe) and the black/white wire at the connector (red probe). Either just the ignition switched on, or engine running is fine too for that test. The result should be 0V, but I suspect you might find some other voltage there.

OK.....I typed up a message and lost it.....here we go again.
Looking at the AlldataDIY for my '96
They have you using a nice "breakout box" which most of us do not have....but I will include some checks they list to the signal wires that I list below....maybe it will help.
I will use signal name in the checks......as I see some mention of possible conflicting information on what wire is what......however I will bet that the values will be comparable.

Without the breakout box.....You may need more than 2 hands for these checks....so a 2nd person will be helpful.

Red wire to MAF pin 2 is +12....power is present when PCM relay is energized.
With the Key OFF.......you should be able to measure continuity (near zero ohms) from this pin to the red wire on any fuel injector or IMRC actuator.....and a bunch of other stuff.
If not.....you have a defective connection or wire.......
Wiggle the wire harness and verify that the resistance does not shoot up as the harness is moved.


Black with White stripe wire to MAF pin 3 connects directly to vehicle ground.
A gentle wiggle check here might be helpful.

Key ON, motor OFF, you should be able to see your +12V (over 10.5V) between pins 2 and 3 in the MAF connector.....wiggle wire harness and verify that the voltage is not jumping around.

Light Blue With Red Stripe wire to MAF pin 5 is MAF Sig....connects directly to PCM Pin 88 and nothing else

Tan with Light Blue Stripe wire to MAF pin 4 is MAF Sig Return.....connects directly to PCM pin 36 and nothing else

Check for shorts on the signal lines......
Key OFF, MAF Connector disconnected from MAF.
Check this on the MAF sensor AND on the MAF wire harness connector (rest of vehicle).
MAF Sig to MAF Sig Return over 10,000 (10K) ohms
MAF Sig to power ground over 10K ohms
MAF Return to Power Ground over 10K ohms
You could wiggle the wire harness for each of these if you suspect a intermitten connection in a harness.

With MAF sensor plugged in.....everything connected.
Key ON, Motor OFF MAF sensor output voltage test (no air moving through MAF)
MAF Signal to Power Ground is to be less than 0.20V

Key ON, Motor Running, everything connected. Sensor output voltage test (air moving through MAF)
MAF signal to MAF Return to be between 0.39V (min) and 3.90V (max)
Wiggle wire harness.....does the voltage jump around?
With vehicle at warm idle......which is somewhere around 700'ish rpm lower reading.....Rev motor up to about 1500rpm......voltage should go up.
DO NOT try to rev up to get 3.90V reading......
If the voltage is below 0.39V and/or above 3.90V, there is a problem.
Wiggle the wire harness.....does the voltage jump around?

Thanks Wiswind, that's useful information and the confirmation that the black/white wire is indeed vehicle ground is handy.

uzzo2 - everything is pointing towards an open-circuit black/white ground wire - I know you already did a continuity check and it appeared to be ok, but the voltage readings in post #9 are saying that it's open-circuit, and I trust the voltage readings.

Do the voltage check which I suggested above in my last post - if the meter leads won't stretch between negative battery terminal and MAF connector then use any good ground point instead of the battery terminal. If you get a reading of 0V then that would suggest the ground wire might be ok after all, but I think it's almost certain that you'll get a reading of a full 12V across the wire, and if so then the black/white ground wire is open-circuit. You could trace the break if you have the time and energy or you might want to just snip the wire at a convenient point, splice in a new section and bolt it to ground. Make it secure and waterproof, and you should find you'll then have the expected voltages and the van will be back to normal.

Thanks Wiswind, that's useful information and the confirmation that the black/white wire is indeed vehicle ground is handy.

uzzo2 - everything is pointing towards an open-circuit black/white ground wire - I know you already did a continuity check and it appeared to be ok, but the voltage readings in post #9 are saying that it's open-circuit, and I trust the voltage readings.

Do the voltage check which I suggested above in my last post - if the meter leads won't stretch between negative battery terminal and MAF connector then use any good ground point instead of the battery terminal. If you get a reading of 0V then that would suggest the ground wire might be ok after all, but I think it's almost certain that you'll get a reading of a full 12V across the wire, and if so then the black/white ground wire is open-circuit. You could trace the break if you have the time and energy or you might want to just snip the wire at a convenient point, splice in a new section and bolt it to ground. Make it secure and waterproof, and you should find you'll then have the expected voltages and the van will be back to normal.
You're right selectron, I checked it this AM, I am reading .05 volts with the red probe of the meter on the black/white wire and the black probe on the ground post of the battery. I guess this would indicate a bad ground, what do you think?

That isn't what I was expecting. The ground wire might be ok after all but something still doesn't add up with the voltages but I can't see what it is. I'll have a think about it and get back to you.

That isn't what I was expecting. The ground wire might be ok after all but something still doesn't add up with the voltages but I can't see what it is. I'll have a think about it and get back to you.
Thanks guys, I really appreciate all the advice. I have a doctors appt. at 11 AM eastern time. When I get back I am going to go over it again and do the checks that wiswind posted, I will post the results here.

From post #4:I can however take the ground probe out of the harness and stick it on the battery ground post and it shows voltage.

And from post #9:Doing this, I have no voltage BUT, I can leave the red probe on the tan/light blue wire and then take the black probe out from the ground wire in the MAF harness and put it on the ground post on the battery and read voltage.

You didn't say what level the voltage was, but that just shouldn't be happening. The black/white wire is vehicle ground - it connects to a ground point which in turn connects back to the battery negative terminal, so whatever voltage you get when the meter's black probe is on the battery negative terminal, you should be getting the same voltage when it's on the black/white wire at the connector - but you're not, and so I still think the ground lead is open-circuit, or possibly the lead itself is good but maybe it's not making contact where the connector plugs into the MAF, so you might want to take a close look at the connector contacts to see if the ground one is corroded or physically damaged.

Go through Wiswind's tests, and if they don't shine any light on the problem then I'd consider temporarily running a separate ground lead to the connector, if you can safely wedge a piece of wire into the back of the connector and ground the other end, and then see if your scan tool data changes.

Okay guys, I got back under the hood today, all the resistance measurements were taken on the 200K selection of my meter.

MAF Sig to MAF Sig Return over 10,000 (10K) ohms
@ the sensor= 3.8, @ the harness= 128.3

MAF Sig to power ground over 10K ohms
@ the sensor= 3.8, @ the harness=128.3

MAF Return to Power Ground over 10K ohms
@ the sensor= 0.00, it ohmed out completely, @ the harness= 29.0

MAF Signal to Power Ground is to be less than 0.20V[QUOTE]
I got 0 volts here

[QUOTE]Key ON, Motor Running, everything connected. Sensor output voltage test (air moving through MAF)
MAF signal to MAF Return to be between 0.39V (min) and 3.90V (max)
I got 1.09 volts here, I did wiggle the harness around while taking these readings and it didn't seem to change anything. And doing this particular test, revving the engine up did increase voltage.

You didn't say what level the voltage was, but that just shouldn't be happening. The black/white wire is vehicle ground - it connects to a ground point which in turn connects back to the battery negative terminal, so whatever voltage you get when the meter's black probe is on the battery negative terminal, you should be getting the same voltage when it's on the black/white wire at the connector - but you're not, and so I still think the ground lead is open-circuit, or possibly the lead itself is good but maybe it's not making contact where the connector plugs into the MAF, so you might want to take a close look at the connector contacts to see if the ground one is corroded or physically damaged.
I am getting 0.15 volts, ironically that's the same exact voltage that I am now getting if I stick my red probe on the black/white wire and my black lead on the ground post of the battery. I did make up a short jumper and stuck it in the back of the harness on the ground wire and stuck the other end on the ground post on the battery. I still wasn't getting any data showing up on the scanner in the MAF section.

Maybe the 0.15 is normal drop.....there are a few wires that go together and some lead length between the ground connection on the MAF and the battery terminal.

Just as a note......from reading the table of voltages vs amount of airflow table for the MAF on AlldataDIY, it looks like the 3.0L and 3.8L use different MAF units......at least they have different values listed in the table.
In other words......for a given voltage.....the 3.8L windstar shows more airflow in the table.....this is for 1996 which has the big intake with the IMRC system.
Hopefully you have the correct MAF for the 3.8L engine for 1995.

Another thought.....maybe your scanner cannot read the MAF on the windstar for some reason?
If the voltage values are totally out......the PCM should set a fault code.
All zeros would surely give you a code.
You could try unplugging the MAF......and verify if you get a MAF failure code.

UZZO

You might have a bad connector or dirty contacts. Do a continuity test between pins 2 and 3 of the MAF disconnected. Then between pins 5 and 3. The resistance should be less than 2 and 3. Then between 4 and 3. The resistance should be less than or equal to 5 and 3. Reconnect the MAF and probe the wires doing the same test. The resistance values should be equal to or less than. If they are greater than you have a bad connection.

Bob

UZZO

You might have a bad connector or dirty contacts. Do a continuity test between pins 2 and 3 of the MAF disconnected. Then between pins 5 and 3. The resistance should be less than 2 and 3. Then between 4 and 3. The resistance should be less than or equal to 5 and 3. Reconnect the MAF and probe the wires doing the same test. The resistance values should be equal to or less than. If they are greater than you have a bad connection.

Bob

Well due to work and inclement weather, I wasn't able to get back on it until today. If it's as wiswind said with the red wire being pin 2, the black/white wire being pin 3, the tan/blue wire being pin 4 and the blue/red wire being pin 5, here's what I came up with.

From the sensor itself between 2 and 3 showed open, no resistance. Between 5 and 3 was 3.7 and between 4 and 3 ohmed out at 0.00

I plugged the harness back in and took the measurements again by back probing it. Between 2 and 3 showed 1.1, What I found strange there was that if I reversed the leads from my meter and put the red probe on pin 2 and the black probe on pin 3 it showed a value of -0.00

I didn't think polarity came into play when measuring resistance but it did in this instance. Between 5 and 3 was 3.6 and between 4 and 3 ohmed out at 0.00

I did as wiswind suggested and unplugged the harness and drove it to town (about 15 miles) and back. I got the P0102 code but no lean codes, I just can't help but think that it has something to do with the MAF sensor or the wiring going to the sensor.