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Electrical loading of MAF sensor output...

Hello there,

I am designing an auto accessory that would respond to the MAF sensor voltage (0-5v analog GM/Bosch style). I will therefore need to tap into the MAF sensor signal which is being sent to the ECM. My question is relating to the input impedance of my accessory. What shall the minimum input impedance be such that the original MAF sensor signal feeding the ECM is unaffected? I cannot find any specifications that deal with this topic.

For instance would an input impedance of 90kohms be acceptable?

Any help or references would be very nice indeed, thx, frenchy

Reply to
frenchy
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The obvious answer is the more impedance the better. Ask Heisenberg. I would imagine that there is not much current in the circuit. Modern Multimeters are 10 megaohms to minimize the effect on a circuit. You load seems a little low but the only way to know is to test it yourself. Apply a load and measure the voltage drop. When it is low enough it is good. I would say not more than .05V.

Reply to
Scott Buchanan

Scott, Thank you for your reply. I do not have any MAF sensors here in my design lab, which is why I am researching this. I want to simulate it here in my lab 1st, then indeed I will test my prototype on real vehicles. Certainly there must be some printed specs regarding MAF sensor output impedances or a discussion on loading.

thx, frenchy

Reply to
frenchy

The ecu is ttl and cmos. I would try to get at least 10 meg ohms. IMO, 90k would NOT be acceptable. Nor would 900k.

Reply to
« Paul »

The higher, the better. 100K would be good, 1 megohm would be better. Be careful not only of loading the sensor with a low impedance but of conducting external interference back into the ECM through your device.

A better (but more complex) solution would be to read the OBD II data and get the air flow value from that, scaled to pounds per second or whatever.

Reply to
Paul Hovnanian P.E.

I would be surprised if there was anything in the public domain. It is too esoteric. The only place you may find any documentation is in the engineering departments of auto manufactures. Not to tell you what to do, but if you are going to properly develop your product, you will need a test bed in your lab. Obtaining parts from a yard would be a good bet. In the mean time, I would tap into the circuit of a car to do the testing and get the information that you need.

If you can share, I am curious what you are doing. If you need a tester let me know.

Multimeters

Reply to
Scott Buchanan

I thought that platinum MAFs had only a few hundred ohms resistance, but according to this thread it's higher:

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Is there any reason why your accessory's input impedance will be 90K? Why can't you use a buffer IC and get much higher impedance/

Reply to
larry moe 'n curly

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