Messages

1

Engine + Driveline / AFM Resistance Readings

« on: August 10, 2010, 10:57:19 AM »

To paraphrase Despair  Inc.'s great poster:  It could be the only purpose of your post is to serve as a warning to others.

Or in the words of the lesser Homer:  "Doh".  Why am I reading resistance across the pins, when with the cover removed, I can read the actual voltage going to the computer.

Swinging the vane open yields a steadily increasing output voltage on pin 2.

So now its back to looking for the true cause of no power over 2500rpm . . . and resealing the air flow sensor's electronics.

2

Engine + Driveline / AFM Resistance Readings

« on: August 09, 2010, 11:24:25 PM »

Thanks much,

After posting, and then looking at the price of a replacement ($600+), I did open the top to examine the electronics.  Everything looked clean and good inside.  The swept area didn't look like it was too worn to function properly.

I sure would appreciate if you could check yours from the M20.  I must admit this one reminds me of my old E12 which must have also been similar.

3

Engine + Driveline / AFM Resistance Readings

« on: August 09, 2010, 01:57:53 PM »

On a friend's '91 318i which won't rev over 2500rpm once warmed, I am trying to diagnose the problem before spending money for parts.

The vane type air flow sensor reads the following resistance between pins 1 and 2 as I test it off the car.
400 ohms with vane closed,   smoothly increasing to
750 ohms at 20 degrees open,
750 ohms at 50 degrees open,
750 ohms at 70 degrees open,  and then decreasing smoothly to
350 ohms when fully open.

What have others measured?  This doesn't sound intuitively correct, but I wouldn't put it past those Bayerischen engineers to do something unusual.

The temperature resistance was spot on at 70F, and I've got exactly 5v at pin 1.