1G What is the best way to test a MAF?

[Echo5Zulu]

What is the best way to test a MAF?

I have a code 12 for the MAF on the logger. I am reading 0hz from the MAF on the datalogger. I have tested all wires on the car. Power wire, ground, and signal wires are all in spec. I have continuity on the wires to the ECU. I have tried swapping another good ECU to no avail. I have tried two rebuilt MAF's one from Cardone and another from Blue Streak but both have Mexico stickers on them and don't look like they have been opened or rebuilt. Temp sensor and barometric sensor work on them but no MAF signal. I also tried back probing the MAF wire to the ECU and only get .03 volts. On other cars they normally get 1 volt or so at idle from my research.

Are there any other ways to test a MAF? What is normal voltage when back probing? Has anyone set up a test bench to test a MAF out of a car? I know I would need power and ground and about 5v signal and maybe blow through it with a fan? Anyone know what the signal power is for?

Thanks for any help you can provide. Been playing with and building this car for twenty years and this issue has me stumped!

 

[steve]

The MAF signal is a frequency dependent pulse train and most multimeters aren't going to provide useful information trying to measure voltage on the pin.

The ECU pulls the signal line up to 5v and the MAF generates the pulses by pulling that down to ground. So with the MAF pin 2 (Green/Blue) disconnected at the MAF you should measure about 5v from the ECU with the ignition on. IIRC, a good MAF will produce a 3Hz pulse train when powered up but no actual airflow so that the ECU can tell if it's working.

MAF Pin 3 (Red) is 12v power from the MPI circuit to power the internal circuits.
The other MAF sensors IAT and Baro are analog inputs to the ECU.

The Turbo MAF has one additional pin that the N/T doesn't and that's the MAF reset Pin 1 used by the ECU to reset the airflow counting circuitry at times like when the BOV is opened due to the throttle closing.

I'm having a hard time believing you have 3 bad MAFs and 2 bad ECUs but it's possible. While it seems like you've checked the wiring I'd look closer at it.

 

[Echo5Zulu]

The MAF signal is a frequency dependent pulse train and most multimeters aren't going to provide useful information trying to measure voltage on the pin.

The ECU pulls the signal line up to 5v and the MAF generates the pulses by pulling that down to ground. So with the MAF pin 2 (Green/Blue) disconnected at the MAF you should measure about 5v from the ECU with the ignition on. IIRC, a good MAF will produce a 3Hz pulse train when powered up but no actual airflow so that the ECU can tell if it's working.

MAF Pin 3 (Red) is 12v power from the MPI circuit to power the internal circuits.
The other MAF sensors IAT and Baro are analog inputs to the ECU.

The Turbo MAF has one additional pin that the N/T doesn't and that's the MAF reset Pin 1 used by the ECU to reset the airflow counting circuitry at times like when the BOV is opened due to the throttle closing.

I'm having a hard time believing you have 3 bad MAFs and 2 bad ECUs but it's possible. While it seems like you've checked the wiring I'd look closer at it.

Thank u for that information. I thought the pin number 1 was the MAF signal back to the ECU. I didn't know it was a reset for the bov. Explains why only turbos have it. That is the one I was back probing.

So is there a signal that goes back to the ECU to tell it flow or does it figure out flow based on a change in the voltage it pushes out to the MAF on line 2 that the MAF puts to ground? Am I able to back probe that wire to see a change? MAF's on other cars you can back probe and get 1 volt at idle and it increases with the throttle. I have 5 volts when I test it with the key set to on so it is in spec and my ground has good continuity.

If the MAF is bad (has an open circuit) and can't flow power from the ECU to ground would my logger read 0 hz like it does?

I'm sure as these cars and components age more and more people will need this information so thank u for sharing.

 

[steve]

There is more information than you need right now in the 1990 Technical Reference Manual but you should read the whole thing. Because it was written as an introduction there are many things that are 1990 specific that changed on the later cars but over all it explains how things work.

1G DSM 1990 Technical Information Manual

Part of the promotional material from Chrysler previewing the then brand new vehicle

www.dsmtuners.com

From your question I don't think you understood what I posted before.

The airflow signal from the MAF to the ECU is on MAF pin 2 going to ECU pin 10.
It's measured in frequency with the signal getting faster as the airflow increases. That's what why the datalogger reports the airflow in Hz (Hertz). Other non-DSM cars may provide an analog output from their MAFs but that not how a DSM works.

Here are the pages from the 1990 DTM on the MAF sensor.

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[steve]

I think I'm confused. I thought the NA MAF and the Turbo MAF shared the same connector minus the unused Reset pin but my 91 ManualCD FSM shows that it's different. I don't know if it's accurate or not. That's part of why I include the wire colors. If this is accurate then pin 1 (Green/Blue) is the airflow signal but it still doesn't have a voltage on it other than pulses of 0-5v that increase in rate as airflow goes up.

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[Spleen8urLSX]

I think I'm confused. I thought the NA MAF and the Turbo MAF shared the same connector minus the unused Reset pin but my 91 ManualCD FSM shows that it's different. I don't know if it's accurate or not. That's part of why I include the wire colors. If this is accurate then pin 1 (Green/Blue) is the airflow signal but it still doesn't have a voltage on it other than pulses of 0-5v that increase in rate as airflow goes up.

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To answer that factory turbo cars and nt cars do indeed have different maf connectors. The nt utilizes a 6 pin connector with all 6 pins used and the turbo model utilizes an 8 pin connector with 7 of the 8 pins used to accommodate the maf signal reset function you mentioned. I don’t remember if they are pinned out the same with the exception of an extra wire or not, I know when I switched this connector on my cars harness (1g nt converted to turbo) all the wire colors matched up with the exception of the wire I had to add but that’s been some time now.

 

[19Eclipse90]

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[04][05][06]​

1G 2.0L Non-turbo MAF pin-out:

Pin 1 - Green with blue stripe, to ECU pin 10​

Pin 2 - Red, sensor power wire​

Pin 3 - Green with red stripe, to ECU pin 23 and Throttle Position Sensor pin 1​

Pin 4 - Green with black stripe, to ECU pins 17 and 24​

Pin 5 - Green with yellow stripe, to ECU pin 16​

Pin 6 - Green with orange stripe, to ECU pin 8​

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[01][02][03][04]
[05][06][07][08]​

1G Turbo MAF pin-out:

Pin 1 - Green with white stripe, to ECU pin 6 for '91+ ECU........ [or ECU pin 14 for '90 ECU]​

Pin 2 - Green with blue stripe, to ECU pin 10​

Pin 3 - Red, sensor power wire​

Pin 4 - Green with red stripe, to ECU pin 23 and Throttle Position Sensor pin 1​

Pin 5 - Empty​

Pin 6 - Green with black stripe, to ECU pins 17 and 24​

Pin 7 - Green with yellow stripe, to ECU pin 16​

Pin 8 - Green with orange stripe, to ECU pin 8​

 

[Echo5Zulu]

I was able to work on the car a little this afternoon. Switched my back probe from pin 1 to pin 2 and fired up the car. It is running a bit high at around 1500 rpm and is putting out around 2 volts which makes sense as most cars put out 1 volt at 750 rpm. So that shows the MAF is good and explains how to test it to see if the MAF is outputting any signal. I also tested and verified that the power and both signal lines were in spec with it unplugged and key set to on. I also verified ground and tested that the temp and barometric sensors are good.

Looks like it's time for me to start tracing wires. Bummer part is I run an SAFC II and it intercepts the MAF signal in order to alter it. Hopefully that unit isn't bad.

 

[steve]

Just for testing bypass the SAFC and see if you start seeing something other than 0 Hz on the datalogger. If you do I'd double check the SAFC settings to make sure it's expecting a Karman MAF and outputting the same.

 

[Echo5Zulu]

I was able to work on the car a little this afternoon. Switched my back probe from pin 1 to pin 2 and fired up the car. It is running a bit high at around 1500 rpm and is putting out around 2 volts which makes sense as most cars put out 1 volt at 750 rpm. So that shows the MAF is good and explains how to test it to see if the MAF is outputting any signal. I also tested and verified that the power and both signal lines were in spec with it unplugged and key set to on. I also verified ground and tested that the temp and barometric sensors are good.

Looks like it's time for me to start tracing wires. Bummer part is I run an AFC II and it intercepts the MAF signal in order to alter it. Hopefully that unit isn't bad.

Just for testing bypass the SAFC and see if you start seeing something other than 0 Hz on the datalogger. If you do I'd double check the SAFC settings to make sure it's expecting a Karman MAF and outputting the same.

Thanks. I see in the SAFC II manual there is a way to see and test sensors so I'm going to check that out first then start tracing and bypassing.

It's been working fine for many years. This latest issue started out as a little bit of an idle surge when I would come to a stop so I thought it was just a small boost leak developing and was going to test it but then one day when I pulled in the driveway it started acting like the MAF went dead and reading 0 hz for airflow.

 

[Echo5Zulu]

Update. Thanks to Steve it's working. He mentioned the SAFC II settings and although I haven't changed that setting in years it somehow wasn't on Karmen. Does anyone know how it could have switched all of a sudden like that on its own? Could a power surge or blip do that?

At least I learned a lot about how to test MAF sensors and how that whole circuit works so hopefully this thread can help others in the future too yet.

 

[DSMPT]

Does anyone know how it could have switched all of a sudden like that on its own? Could a power surge or blip do that?

The SAFC with a screen which is the SAFC 1/2 and Neo have an EPROM inside. It should keep your setting without power until you reset the unit or make a change. So if you are sure that you or anyone didn't accidentally change the setting, you should inspect it. And repair or replace if necessary. In case if this happened accidentally, you can lock the setting by a password.