[urq] Update on my MAC-02, stuck duty cycle problem

[Craig Cook]

Alex,
 
Just a thought. If the car is running rich the 02 voltage should be > 0.7 volts. If the 02 sensor is faulty ( voltage not switching) the computer will want to see the higher voltage and try and drive the voltage up by increasing fuel. Checking the 02 sensor with a volt meter is not very accurate. I realize that that may be the only tool you have for checking the sensor with but the voltmeter only averages the signal. A proper check would involve hooking up a lab scope and checking the signal that way.
I don't know what kind of voltmeter your'e using but the cheap meters tend to update the signal very slowly and can lead to mis- diagnosis.
Alex, feel free to call me at work if you want to. I would also be checking the resistance of the wire from the 02 signal wire back to the Mac 02.
 
I hope this helps.
 
 
cheers,
 
Craig Cook.

alexander stickler <a_stickler at yahoo.com> wrote:
Hi guys,

Thank you to all of you who came through with an offer
to loan me a MAC-02 to diagnose my fuel injection
problem whose major symptom is running rich, and with
the duty cycle stuck at 50% even with some throttle.
It stays at 50% until the full throttle switch bumps
it to 76%.

I swapped Mike Hopton's later MAC-02 in, which worked
beautifully after disconnecting the wire at pin 2 and
swapping #5 and #6. 

However, the duty cycle is still stuck at 50%.

The 02 sensor works, I've got voltage there (small
voltage). The idle switch is closed and functioning at
idle and the full throttle switch closes when
triggered. Unless Mike's loaner ECU is equally bad,
the ECU does not appear to be at fault.

So, what the heck else could put the duty cycle into
'protect' mode and keep it from changing except when
trigger by the FT switch?

The car's in the garage for the winter, but 'I need
closure.' 

Any thoughts on this would be greatly appreciated.

Cheers,

Alex
'83 URQ






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