Testing my MAF sensor. Help!

Acousticplayer

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Hi everybody..As I continue to chase down my elusive misfire I am testing my MAF sensor using a multimeter as described in a number of u-tube videos. As many will probably know ,the sensor has three terminals .If I understand it correctly one is the 12 volt supply one should be ground and the third should be the signal. The 12 volt supply is located on the right side looking face on, however both the remaining terminals come up positive for continuity indicating both are ground. Surely this can't be right. Have I got a short somewhere ?
 

Pingu

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Are you just doing the beep test, or are you measuring the readings? The wire is heated using the 12v and earth, and the signal is measured using the signal wire and earth. All three pins are connected to each other, but there should be a change in resistance between the signal pin and the earth pin when the wire is cooled by moving air.

Assuming...

Pin 1 = 12v supply
Pin 2 = Signal wire
Pin 3 = Earth

Connect pin 1 to 12v on a battery and pin 3 to the negative terminal. Test resistance between pins 2 and 3, and blow over the MAF wire. If the resistance changes, the MAF is working...

 

Acousticplayer

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Hi again. Looking at my post I think I may have not explained myself too clearly. I didn't actually do any tests on the MAF itself. I tested the harness to find the live and ground terminals. It was disconnected from the MAF. As said looking at the disconnected plug face on ( IE looking at the pins ) the right pin showed up as positive but the centre and left pins both beeped when connected to the right hand live pin.. Does this alter your views please.
 

NZ00Z3

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I have set up a MAF testing system. The owner of the car runs some cheap phone app software and logs the operation of the engine under certain conditions. I review the logs and tell you what I see in them. One of the logs is specifically for the MAF. I have a MAF model that I compare your MAF's performance to. The other logs are for the general condition of the engine.

As you are having a long term issue with your car, it might be a good option for you.

Read this thread, including the PDF at the end, to find out more about OBD Fusion and how to use it. https://www.e46fanatics.com/threads/obd-fusion.1240733/#post-18380161
 

Acousticplayer

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Hi NZ. Yes I looked at OBD fusion when you replied to one of my earlier threads and have kept it in mind. As you say I've been chasing down this problem for a long time and am anxious to get it sorted but it's proving difficult as the problem keeps disappearing. I want to complete the test on the MAF and also do a smoke test during the next week or so. After that I'd be very interested in going down the Fusion route,it sounds interesting. Thanks.
 

Pingu

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Hi again. Looking at my post I think I may have not explained myself too clearly. I didn't actually do any tests on the MAF itself. I tested the harness to find the live and ground terminals. It was disconnected from the MAF. As said looking at the disconnected plug face on ( IE looking at the pins ) the right pin showed up as positive but the centre and left pins both beeped when connected to the right hand live pin.. Does this alter your views please.
Testing the way that you did can cause you problems.

It sounds like you connected a 12v+ pin and an Earth pin through the Resistance setting on your ohmmeter. This could kill your ohmmeter. This test should be done on the 0-20vDC Voltage setting.

The only tests that you can do with your ohmmeter and the open cable are a test for 12v on the live pin and a test for earth on the earth pin. You can also do a continuity test on the signal pin, but you need access to the pin going into the control module.

All of these tests are flawed, as a single strand of wire would allow the test to "pass", even though the wire is close to failure.

The correct way to test is with a low wattage test bulb (like a dashlight bulb).

Connect one end of the test bulb to the 12v+ on the cable and the other to the earth pin on the cable. If the bulb lights, then both wires are good. If the bulb doesn't light, disconnect the earth pin and connect the test bulb to a good earth on the car. If the bulb lights the 12v+ is good and the earth wire is probably faulty. Confirm this by connecting the test bulb to the earth pin and a known good 12v+ supply (the jump point is a good supply).

Assuming all has passed, the only way to test the signal wire is to test for continuity between the ECU and the plug - (THIS MUST BE DONE WITH THE ECU PLUG DISCONNECTED). 12v+ --> Test Bulb --> MAF Plug Signal Wire --> ECU Signal Wire Connector --> Good Earth = Bulb Lights

The last test is a last resort, as the Blow test should have been done first. You can do a Blow Test on the car (with everything connected), but you have to be very careful...

Set the Voltmeter to DC VOLTAGE.
Use a pin or needle to carefully pierce the signal wire in the loom near the MAF.
Connect one of the voltmeter cable to the pin (or needle)
Connect the other voltmeter cable to a known good earth.
Confirm you are on the VOLTAGE setting - THIS IS VERY IMPORTANT as the resistance (beep test) setting uses the internal battery to power the ohmmeter, and this battery together with the car battery may supply too much power into the ECU.
Start the car.
If the signal voltage changes when you rev the engine, the MAF is working.

What you don't know is whether it is working properly. If it has a dirty "hot wire", then the voltage changes will be smaller than they should be, as the wire is being insulated by the dirt, and isn't cooling down as quickly as it should. This is where @NZ00Z3 and the software would really help, as this would show if the readings are out of spec. His software would also show if the ECU is working as expected.

In short, plug in the computer :ymdevil:
 

Acousticplayer

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Hi Pingu. Wow you've certainly given this some thought for which I thank you. This is a lot to take on board and I'm going to have another look tomorrow. Can you say what level of resistance (ohms ) I can expect to see between earth and signal wires on the blow test. I did mock something up today on the bench and was getting a reading of around 200 ohms but the set up was a mock up and not sure how accurate it was.
 

Pingu

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Hi Pingu. Wow you've certainly given this some thought for which I thank you. This is a lot to take on board and I'm going to have another look tomorrow. Can you say what level of resistance (ohms ) I can expect to see between earth and signal wires on the blow test. I did mock something up today on the bench and was getting a reading of around 200 ohms but the set up was a mock up and not sure how accurate it was.
My video shows the readings of my MAF. I would expect similar numbers, even though my MAF has four pins. Mine has a negative signal wire that returns to the ECU, whereas yours uses a common ground .

Mine was around 200 when blown.

Use electrical contact cleaner to clean the hot wire.

 

Acousticplayer

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Hi Pingu. I'm working on this at the moment.Ive done the bulb test and that looks ok with the bulb lighting up nicely. I've hesitated doing the signal wire test as the harness wire is so thin I want to avoid damaging it. I'm going to do the MAF blow test again but before I do could you clarify something for me please. In your first reply you suggest I check the resistance between pins 2and 3 and refer me to your video. However in your video you are checking voltage. I've tried checking resistance but with not much success. On static it shows around 200 ohms when I blow into it it goes into open loop as though it's off scale . Does this on all ranges. Thank you.
 

Pingu

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Apologies if I misled you. I was wrong - it is VOLTAGE that you read with a powered MAF. As I said in a later reply, measuring resistance on a powered circuit can lead to all sorts of problems.

Your MAF has passed the blow test. The wire is changing resistance when it is cooled - that's the test passed.

Unless you know what the absolute values should be, you can't test it further. You have confirmed that there is a relative change.

With all tests passed, the only thing you can do now is plug in the computer. INPA knows what the absolute values should be and shows a meter that moves from Red to Green, dependent on value. It's very good...

 

Acousticplayer

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Hi again. Thanks so much for your help and patience. Would love to have INPA. Looked into it sometime ago,couldn't find where to download it and it looks very complicated. Might try explore it again. Best wishes.
 
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