What the dwell?

[Jonathan]

So, on today's episode of "The Bold and the Beautiful but Restless Idle"... here's my current dwell meter readings:


https://www.youtube.com/watch?v=KHZQjjeKSE0

I edited out quite a bit, so to summarize, car was started from cold (sitting overnight) and I ran it idling for 8 minutes. Up until about the 1:45 mark, it was steady at 51 (read on the 8 cylinder scale and then multiplied by 2). At about 1:45, it went down to a steady 43 and continued as such until about 5:30 real time of the car running. At around 5:30, it then dropped to pulse for about one minute between 30 (or 35) and up to 43 (on the meter that would be down to 15 or a little higher and up to 21.5). Then, after one minute of pulsing, it went back to a steady 43 for the remainder of the time it was running and I shut it off after 8 minutes total.

On the video, the first 10 seconds is the steady 51, then next 15 seconds is the steady 43. Then I cut out the minutes in between, and soon after the cut, it pulses for one minute between 30-43, and then the last few seconds on the video is back to a steady 43.

Some context: car drove nice the day before to a car show about 15 miles away. No "day changing" issues there or back, but each way I felt like while just starting out and most noticeably when at lower speeds, it felt sluggish, like it had less power than usual.

Now, my usual might not have been "normal" after just recently realizing my full throttle enrichment microswitch was sticking in the engaged position. This is the lower switch on the auto with the flap on it and the tiny plunger that is supposed to get pushed in and spring back out was springing back out because it got gummed up somehow. Probably from me trying to spray lube on the throttle spool and spring nearby.

I unplugged the bad switch and left the good switch plugged into the kickdown microswitch that ties into the auto trans.

So, my idle and dwell has been a bit of a moving target after realizing a couple things recently. Not easy to nail it down completely, but now I wonder if indeed the O2 sensor got fouled from extra fuel, etc.? I suspect there is a pretty good chance of this, especially considering my dwell swings fine for a while but then doesn't for other times and I hadn't touched a thing at any point. Not sure if they can fail this way, intermittent that is. It would potentially explain why the car feels sluggish at times, but then comes and goes.

What do you think?

[DMCMW Dave]

The first 10 seconds is likely the cold enrichment switch holding it "rich" (55), then that warms up and goes to open loop and sits at 45. That's a bit unusual, what is your overnight ambient temperature? Holding 45 means the ECU does not "see" the O2 sensor.

The starting at 45 and then dropping to the bottom, and then jumping back to open loop is still indicative that it's too rich. As it seems to go back to open loop while idling ("cold" O2 sensor) that implies that the O2 sensor is fouled. I'd call it a lazy sensor and replace it. Running rich a long time will foul the sensor and they don't seem to come back. This is why later cars went to heated O2 sensors (and why modern sensors have more than one wire).

If you want to play with the electronics a bit, (this is actually in the manual!) disconnect the O2 sensor. Now ground the lead that goes to the ECU and watch the needle and listen to the FV. Then take a 1.5V battery and connect (-) to ground and (+) to the ECU lead, the meter will swing entirely the other way. You will hear the FV change in tone as well. This confirms that the ECU is working.