O2 sensor question

[KandJinmaine]

I've been having an issue with a '80 FI spider that starts fine and runs good for about 4 minutes and then, with amazing repeatability, runs rough and when driven acts like it hits a rev limiter if you give it too much gas. I've started checking the values from various sensors at the ECU connector and haven't found anything too weird but decided to change out the oxygen sensor as it was old anyway. I've only test driven it once but it seems to have cured the issue. My theory is that when the sensor got up to temp (after the 4min.s) it gave bad info... Anyone else had these symptoms? Comments on my logic?
Thanks to Brad Artigue!!
Jeff

[RRoller123]

Check the water temp sensor in the union up front top of the engine. It can be pulled and put into boiling water and the Resistance read.

[KandJinmaine]

Thanks for the tip, I'll give it a shot this weekend.
Jeff

[wizard124]

The ECU shuts off the O2 sensor circuit at full throttle via the throttle plate switch. So, the rev limiting issue you describe, at full throttle, can't be caused by an O2 sensor.

[KandJinmaine]

Thanks for the input Wizard, probably not the best way to describe the symptom. The motor seemed to be getting too much fuel, and then would hesitate, making it it sound like a rev limiter. Might also be because we are running an empty cat and a small glass pack . I just got back from ride #2 since replacing the O2 sensor and it is still fixed ( as he says another prayer to the God Italian Motoring). Just trying to figure out why....
Thanks
Jeff

[wizard124]

Thanks for the input Wizard, probably not the best way to describe the symptom. The motor seemed to be getting too much fuel, and then would hesitate, making it it sound like a rev limiter. Might also be because we are running an empty cat and a small glass pack . I just got back from ride #2 since replacing the O2 sensor and it is still fixed ( as he says another prayer to the God Italian Motoring). Just trying to figure out why....
Thanks
Jeff

That throttle plate switch is an easy check and adjustment with a multi-meter. Many links on-line for procedures and function.

Have you checked idle timing and advance function?

[KandJinmaine]

Yep,been there, did that. After a couple more semi-spirited drives( alignment tomorrow), it's still running great. Just trying to make sense of the O2 sensor being the culprit, and why it turned to crap after warm up before. Oh well, you can't (or shouldn't) argue with success! I forgot what a joy this car is to drive and how it makes my wife smile when she is behind the wheel. It's been a couple of years since its been roadworthy, and it's great to have it back.
Thanks again,
Jeff