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Discussion Starter · #1 ·
Does anybody happen to know what are the expected resistance values for a MAF sensor? I'm troubleshooting an issue and just want to make double dog sure before I go spend $100 on a new sensor. Below are the values I measure. I noticed that polarity does make a difference, although I'm not sure why. Maybe there are diodes in it. The letters reference the connector on the sensor.
A = Red (power)
B = Black/white
C = Tan/blue
D = Light blue/red

Resistance:
A-B: 7.9M ohm
A-C: 7.9M ohm
A-D: 7.9M ohm
B-A: 2.5M ohm
B-C: .1 ohm
B-D: 3.9K ohm
C-A: 2.5M ohm
C-B: .1 ohm
C-D: 3.9K ohm
D-A: 2.5M ohm
D-B: 3.9K ohm
D-C: 3.9K ohm

The first three values appear to represent the resistance from power input to signal return, if I'm interpreting the EVTM correctly. That would mean that the signal is in the micro-amp range (if these were the correct values). I'm used to 4-20mA as a standard, or 0-10V. Micro-amp signals seem unlikely.

For comparison, I checked my Explorer MAF and got:
A-B: 3.8K ohm
A-C: 3.8K ohm
A-D: 112K ohm
B-A: 3.7K ohm
B-C: .2 ohm
B-D: 110K ohm
C-A: 3.7K ohm
C-B: .2 ohm
C-D: 110K ohm
D-A: 112K ohm
D-B: 110K ohm
D-C: 110K ohm

I do measure power at pin with the connector disconnected. I don't really want to use a wire-piercing probe to check outputs on pins B, C and D with the connector installed for fear of starting corrosion. I wish Ford would put proper breakouts for troubleshooting.

I'm thinking the MAF is kaput. Any comments? Thanks in advance.

I do intend to check that the signal is making its way back to the PCM, but those high resistance values seem awfully suspicious to me.
 

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You aren't going to be able to measure it like that. Tou're measuring the output impedance of an op amp that's powered down, the readings are pretty rando; but they should be the same over different ones.
If you remove it and look at the element, it's a platinum RTD, mounted on arms, which feed the circuitry.
I have read somewhere that the MAF loses it's **** when it tops out at 5V.

If the sensor has continuity, it is good.
Be careful, it's delicate.

I'm thinking it's below 100 ohms.
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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There are some voltages listed in this article, but I'm not sure how accurate they are. In general if the MAF sensor is bad, you'll have better driveability on the street with it unplugged (idle may or may not improve).
 

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After looking at the wiring, I'll stand on what I said. A 5V signal would peg it with a 10V supply.

You always want any sensor to rub the 60% to 80%rangeof the thing the engine wants/ :)
 
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Do you use the Torque app to datalog? I was troubleshooting a lean or rich (can't remember which) CEL code when I bought my current Cougar. My fuel trims were very high, replaced all my vac lines & checked for any vac leaks. Ultimately, replaced the MAF and it cleared up. There was a K&N filter installed, I'm thinking the oil killed my MAF.
Back to Torque, it logs air flow rate and I remember it looking very high in the data. I'll look for my old logs and see what kind of flow you should see.

Also, this probably is in uA range or at least very low mA, I would think 4-20mA would be way too high for the ECU to process. I think only 1 of those connections would be the MAF signal, there is also a temp sensor in there.

Screen shot of recent data: Left is flow rate gallons per second; right is RPMs. Hopefully this gives you something to go on.
1626798424138.png
 

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The way those sensors work is they are fed a constant current whicj heats the element; Blowing air across it makes the element cool,so it jacks up the current to maintain the heating of the element at a constant rate. the 0-5V signal is derived from the control circuit as proportional to the airflow.
 

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It's also not a linear relationship between airflow and voltage; twice the voltage does not mean twice the airflow.
 

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Discussion Starter · #8 ·
Op amp?? Of course, I should have expected that it couldn't be as simple as what's shown in the EVTM. Some of the sensors we use at work have software in them. Seems like everything these days has to have a chip/microprocessor or some other silicon gizmo. I'm a dinosaur. I like simplicity.

I checked the wiring as best as I could with a DMM and without piercing the insulation. I'm not tooled up with one of those devices that can put a current on a wire and measure voltage drop and no access to TDR. Checking for power and continuity showed good.

I finally broke down and bought a scanner that can display live data and plot. I looked at the MAF and it was flatlined. No response to throttle change. I forget the exact units (lb/min probably) but it was .26 with it connected and somewhere around .45 when disconnected. Odd, but maybe .45 is a default value. Anyway, a flatlined sensor is highly suspicious to me.

I'll look into that Torque app some more. It looks like it's for Android devices, which I don't have. I'm wondering if I could run an emulator on a laptop. Of course, that means I would need a laptop. I keep waiting for a hand-me-up from the kids but that hasn't happened yet.

Thanks for the pointer to that tech article. I actually looked at that before I stated troubleshooting, but I'm paranoid about piercing the wiring insulation to check those voltages. In the past, I have gone to the junkyard and bought connectors so that I can make a proper breakout cable, but there's no connector to match what's on the MAF sensor itself. Getting the shipside connector is easy enough.

Anyway, thanks for all the replies. I think with a non-responsive MAF, I'll replace it and hope that it's not a wiring problem that I couldn't discover with the limitation of my crude tools.
 

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You should get a check engine light if the MAF is truly bad. But not for one that's out of range, or one that causes WOT pinging, which these cars are famous for. These factory MAF's do not perform like new for long, I wouldn't hesitate to put a new one in.

I am assuming the MAF wire is clean? You need a tamperproof Torx bit to remove the MAF. The latest one I bought didn't come with a housing, which I would never bother to remove from the car anymore since it's a royal PITA, and that hose is getting dry with age.

Al
 

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I'd go to a junkyard, and get one from a mustang,cougar, or bird from 96 to 98. a2002 mustang maf and tube/airbox is a nice upgrade, but it requires a tune.
I'd do the upgrade if you're going to add power.
 

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Discussion Starter · #11 ·
The MAF is clean. I did get a MAF code, but I don't know if that was because I set it when running with it disconnected. I've been troubleshooting and didn't notice exactly when it appeared. I hooked up my scanner to my Explorer and plotted the MAF output and revved the engine. No comparison. The TBird MAF is definitely not responsive.

I pulled one from the junkyard, but they wanted $45 or $50 and a new Delphi was $80 so I went with the Delphi. I've never had a MAF fail but I didn't want to pay more than half price for something that may not have much life left in it. Delphi's not OEM and I'm always leery of aftermarket parts, but there's not much choice anymore. We'll see what happens in a couple days when it shows up.
 

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I also got a Delphi. It eliminated the WOT pinging that suddenly popped up. Paid for 89 octane for a year. Being able to switch back to 87 octane will pay for the MAF in a year or so.

How in the world did you get it for $80? Autozone wanted $120, but with the discount, I got it down to $106. Rock Auto or e-bay special? Good luck with that, lol!

Al
 
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