US 3.2 V8 runs OK until warm ...

Sounds like a fuel injector issue to me.
The warm up injector is keeping it going until it turns off.

Try having the injectors cleaned.


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If your 328 runs well during that first couple of minutes after cold start-up, your symptom implies things like:

1. the air injection system is not shutting off completely when it transitions to warm-running (or parts of the air injection system and/or exhaust sampling tubes have rotted and fallen off leaving a gaping hole). Letting extra air into the exhaust stream during warm-running with fool the O2 sensor to report things are too lean to the ECU -- so the Lambda system will (wrongly) try to add extra fuel. One easy way to check this is to unplug the single sensor wire from the O2 sensor during warm-running (which disables the Lambda system). If it runs well with the O2 sensor unplugged when warm = most likely air injection system is leaking into the exhaust or O2 sensor bad.

2. If it still runs poorly with the O2 sensor unplugged when warm (but runs well after cold start-up), then I'd be more suspicious of the WUR being wacky - so would confirm/deny the cold and warm control pressures.

Good Hunting!

 

The thermocouple measures the temperature of the exhaust gases just downstream of the catalytic element inside the catalytic converter -- its purpose is to detect if unburnt fuel is wrongly burning inside the catalytic converter. Removing it should have no effect on the engine operation other than letting exhaust gas out -- which is not a good thing.

The O2 sensor measures the oxygen content of the exhaust gases and supplies a voltage signal to the injection ECU that varies from 0.1~0.5VDC (lean) to 0.5~0.9VDC (rich). The injection ECU then sends a signal to the frequency valve to either add fuel or reduce fuel as it tries to keep the O2 sensor signal at 0.5VDC. (I didn't suggest removing the O2 sensor -- just unplugging the single wire that comes from the O2 sensor.)

 

but this sounds as if engine running problems exist no matter if after warming up or starting from cold ... ?


what you can check easily:

1) frequency valve buzzing when engine is running ?

2.) auxilliary airvalve always open ? (pinch hose from valve to plenum after engine warm up)

3.) cold start valve leaking ? (take off electrical plug from valve before starting engine from cold)

 

Why did you replace the O2 sensor without testing? You never gave a result for "If it runs well with the O2 sensor unplugged when warm..." -- did you not ever get the result for this condition?

 

I disconnected the 02 sensor (at the suggestion of a very good F mechanic) and the car (‘85) runs great and starts when hot. I am also not running a catalytic converter.


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