"89 Carrera VAF Sensor Test

[big911fan]

I'm in the process of testing the various sensors on my DME system. The IAT and the CHT resistances tested perfectly according to temp specs. The VAF voltage test showed 4.3v. The Bentley manual specs say it should test "approximately" 5.0v. Another part of the manual just says 5.0v. Two questions:

1. Is 4.3v "approximate" enough? Or should it really be closer to 5.0v?

2. Does the VAF get it's current directly from the DME or from the main/fuel relay?

If it gets it from the main/fuel relay I'm wondering if the relay is getting tired. Easy enough to change out and re-test. If 4.3v is too low and the signal is from the DME, then what? The car seems to be running fine so maybe I'm worried about nothing. Just want to know the status of my 20 year old system.

[Targa Me]

My 84 Carrera measures 4.3v at the VAF.
my .02

[big911fan]

Thanks for the reference reading. I hoped someone else had a reading to compare to. Sounds like 4.3v is normal and is "approximate" according to Bentley.

[rcaradimos]

Bump,

I just checked mine and have no reading of voltage with the ignition on. the resistance is OK on IAT and CHT. With no voltage @ terminal 3 to ground what is going on??? rich start???
Please advise.
Thanks

Duh!! I need to check voltage at connector not sensor.

[911st]

Not sure if this is what you are working on.

Usually the issue is not the Gross AFM Voltage. It is brakes in the contacts along the range of motion in the AFM that comes in the section from frequent movement from idle to cruse.

I think you can use a 9v battery and volt meter and test the AFM by moving the metering door slowly by hand and watching that the voltages progress smoothly.