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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10379 Location: Sunshine Coast B.C.
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Posted: Thu Aug 20, 2020 2:26 pm Post subject: Mk3 4 Pin MAF: Pin 2/4 Resistance? |
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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 |
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Butcher Samba Member
Joined: December 05, 2015 Posts: 1285 Location: Right Here
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Posted: Fri Aug 21, 2020 6:55 am Post subject: Re: Mk3 4 Pin MAF: Pin 2/4 Resistance? |
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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. |
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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10379 Location: Sunshine Coast B.C.
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Posted: Fri Aug 21, 2020 10:40 am Post subject: Re: Mk3 4 Pin MAF: Pin 2/4 Resistance? |
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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 |
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Butcher Samba Member
Joined: December 05, 2015 Posts: 1285 Location: Right Here
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Posted: Fri Aug 21, 2020 6:56 pm Post subject: Re: Mk3 4 Pin MAF: Pin 2/4 Resistance? |
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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. |
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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10379 Location: Sunshine Coast B.C.
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Posted: Fri Aug 21, 2020 8:23 pm Post subject: Re: Mk3 4 Pin MAF: Pin 2/4 Resistance? |
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Butcher wrote: |
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. |
I could've been clearer.
Test situation: MAF disconnected, VOM measuring resistance (presumably of hot wire) at MAF pins 2 and 4.
I could be wrong but it's my understanding that when a VOM is set to measure resistance, it uses the internal battery to put a voltage across parts involved.
Neil. _________________ 1981 Westy DIY 15º ABA
1988 West DIY 50º ABA
VE7TBN |
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Butcher Samba Member
Joined: December 05, 2015 Posts: 1285 Location: Right Here
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Posted: Sat Aug 22, 2020 8:15 am Post subject: Re: Mk3 4 Pin MAF: Pin 2/4 Resistance? |
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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. |
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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10379 Location: Sunshine Coast B.C.
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Posted: Sat Aug 22, 2020 10:38 am Post subject: Re: Mk3 4 Pin MAF: Pin 2/4 Resistance? |
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Butcher wrote: |
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. |
Thanks for that.
Yeah, just wanted to compare new MAF "out of the box" to old
Vanagon is currently not insured so it can't really be road tested beyond driving up a long driveway. So, short tests like that may not allow for the ECU to do any real adaptation to MAF, if that even happens.
Neil. _________________ 1981 Westy DIY 15º ABA
1988 West DIY 50º ABA
VE7TBN |
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