Mk3 4 Pin MAF: Pin 2/4 Resistance?

[Vanagon Nut]

Hi all.

For a Jetta 2.0 engine conversion on a Vanagon.

Bentley diagrams show MAF pins 2/4 for 2.0 OBD1/2 going to ECU.

I realize this isn't how a MAF is tested but bench test measuring of old Bosch MAF vs generic new, VOM set to K Ohms:

old Bosch: 1.78 Ohms so ~ 1800 Ohms

new generic: no reading (I'll double check. edit: nope. Nothing shown with VOM set to K Ohms or Ohms)

Shouldn't the new MAF show a resistance value at (presumably) pins for the hot wire or film? Or, hot wire type should show resistance, other should not or vice versa?

Thanks

Neil.
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[Butcher]

I do not know the answer to your question but the ECU uses voltage [and newer ones use frequency] to measure the mass of air. I tend to measure what the computer wants to see. I also tend to perform a voltage drop test to check the resistance.

When you say generic, do you mean cheap junk? If the brand is too lazy not to put their name on their product, I tend to run away from that product. A MAF sensor is way too important to go cheap on.

[Vanagon Nut]

Thanks Butcher.

The new ~ $60 CAD MAF has a brand name and will be used as a "lazy mans" test MAF and possible spare.

I now wonder if putting VOM voltage across (presumably) the hot wire pins risks damaging that part(s).

The engine starts, idles with the "cheap" MAF but lags a bit "off the line". Maybe ECU is adapting to new MAF specs?

I found this test method useful. If my tests were accurate, the old MAF spec'd out a little low. Can't recall at what RPM though.

http://faculty.ccp.edu/faculty/dreed/Campingart/jettatech/maftesting.htm

He also has some other great "how to's" for the ABA:

http://faculty.ccp.edu/faculty/dreed/Campingart/jettatech/t-belt/index.htm

Neil.
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[Butcher]

I can't see how a volt meter is going to overload the circuit. Just make certain the meter is on voltage and not amps.

[Vanagon Nut]

[Butcher]

I'm sorry. I thought I was talking about measuring the voltage of the signal wire and that would imply that is was plugged in. I also mentioned that I think checking the resistance is not an ideal way of testing that circuit. The circuit is too complex and I could not imagine the value would be worth much during diagnosing.

I highly doubt if you are checking the sensor with an ohm meter that it will damage the circuit.

Back in the days when I worked with Mercedes, the only proper way to test a MAF sensor was to check the power supply/ground. The signal wire was tested with the key on, engine off. With no flow, the signal wire would be 1.0v. If that values varied more than .03v [+/-] the MAF sensor was bad. That was a Bosch test that had to be done if you wanted to warranty a MAF sensor. The air temp sensor was tested with an ohm meter.

I understand that VW does things differently, but assuming that the test is valid, I suspect the signal voltage would be the same from both meters in the same 0 rpm situation. I'm not certain if that meter uses a frequency signal but I suspect it does not.

[Vanagon Nut]