[urq] URQ intermittant duty cycle

Craig Cook craigcook at rogers.com
Tue Nov 15 17:29:19 EST 2005

Sounds like your car is leaning out. I'm assuming that you checked fuel pressure and flow?
When your duty cylcle goes to 99% the frequency valve is fully open. That's probably why you can't hear it buzzing. It could possibly be a airflow meter not always opening all the way. When you rev the engine your'e forcing the airflow plate open. I would suggest double checking the fuel pressures again if you haven't already . Try and keep the gauges on for a while, while diagnosing the problem. I have changed airflow meters for similar problems and this fix cured the problem. In my case the engine would go lean with anything over 4lbs of boost. Even after inspecting the airflow meter I still couldn't see anything wrong with it, but a loaner one fixed the car.

urq <urq at pacbell.net> wrote:
... perhaps, but sometimes you need to be careful to determine which is 
causing what ... which observation is the cause and which is the effect. If 
it is in any way possible I'd recommend that you try to activate the 
diagnostic mode in the ECU ... WOT and Idle switches closed simultaneously. 
This mode should force the ECU to 50% duty cycle ... if the FV still doesn't 
buzz I'd say that your ECU is suspect. If the duty cycle behaves as it 
should perhaps you want to look for a short circuit in the shielded line 
that goes from the OXS connector to the ECU ...

Steve B
San Jose, CA (USA)

> Tonight I monitored the O2 sensor and found that when the idle (or
> acceleration) goes weird, the O2 signal goes to zero as well. Cool I 
> thought, so I
> replaced the O2 sensor and thought I had my smoking gun. No Joy. It still 
> acts
> up, with the duty cycle going to 99 and O2 signal going to steady .003.
> When everything is good the O2 reading varies from 0.2 to 0.7 and the freq
> valve buzzes away. When things are bad the FV goes dead quiet.
> It is sporadic, and on some instances revving the engine will bring it 
> back-
> sometimes not.
> What could cause this? Is this the dreaded ECU duty cycle signal failure? 
> If
> so, why would the O2 signal go south? Do I have 2 equally bad O2 sensors?

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