Dwell reads 49 with o2 sensor grounded

[Ron]

Guessing, 50-100 RPM. If the fluctuation's average RPM drops any, skip to the next cylinder.
(You should be able to hear a change at the good cylinders.)

[David T]

If the timing is off it would affect all of the cylinders evenly. You have to look at each cylinder and see which one (s) are the ones not working as hard as the others. That starts with a compression test. You can also try checking each one with an infrared temp gauge and see if one is colder than the others.

As for the idle and Lambda systems not responding fast enough, that is exactly why you have the hunting. They don't respond fast enough, by the time they respond, you are already firing on another cylinder.

[Jonty]

If you might be having a misfire first pull the plugs as often the misfire will show up as a wet or dry fouled plug that looks different from the others. Also a inline spark tester can help check if the issue is the spark plug itself or the supply to the spark plug. I’ve never had much luck simply pulling the plugs to hear for a change in rpm. I’ve found if you have a misfire dropping from 5 to 4 cylinders is sometimes not easy to hear.

I had a wide swinging dwell and it was a result of poor injectors and a misfire. The misfire was actually a broken plug wire and also a bad injector. I would also replace the 02 sensor just for peace of mind but first fix the misfire or you might foul up the new o2 sensor.

[CFI]

I would also replace the 02 sensor just for peace of mind but first fix the misfire or you might foul up the new o2 sensor.

She already replaced the sensor.

[DaraSue]

Haven't tried the compression check yet but I pulled the plug on the cylinder that had the leaky injector seal and it was pretty cruddy. I cleaned it up as well as I could with a wire brush and put it back but I'll probably order some new plugs just in case. I didn't check every plug but the one next to the dirty one looked normal.

I drove the car to the gas station and back and it felt a little peppier but I still think I'm hearing that popping noise when I rev the engine. I'm not really noticing the other symptoms on this list: https://carcarehunt.com/blog/car-mis...ow-to-fix.html

The rpm fluctuates a little at idle but it stays between about 600-900. It doesn't accelerate noticeably worse than it ever did or die at idle. My fuel economy had gotten worse in the last year or so though (down to low 20s from close to 30 on the highway).

The guy at the shop who told me it was a misfire was the owner and not really an actual mechanic, I'm wondering if maybe it's actually something else? I found a loose nut on the exhaust manifold so maybe I had a leak.

[David T]

If you have been watching your mileage and notice it is lower than usual, it is a sure sign that you need a tune-up and/or your brakes are dragging.

[DaraSue]

Oh, forgot to mention, my timing was slightly off (between 14 and 16) so I adjusted that too.

I'd notice other symptoms if my brakes were dragging, right?

[CFI]

Oh, forgot to mention, my timing was slightly off (between 14 and 16) so I adjusted that too.

I'd notice other symptoms if my brakes were dragging, right?

Yes, especially if it’s a front brake. The car would pull towards whatever side was dragging. Also, depending on how badly it’s dragging and how far you drive, that brake would get very hot and would smell terrible. Acceleration would also be affected but you said that seems normal.

[DaraSue]

Yes, especially if it’s a front brake. The car would pull towards whatever side was dragging. Also, depending on how badly it’s dragging and how far you drive, that brake would get very hot and would smell terrible. Acceleration would also be affected but you said that seems normal.

Ah, OK. I think I can rule that out. Braking seems normal and I drove it to Wendover last month (100 miles each way) and didn't experience any of that.

[Bitsyncmaster]

Ah, OK. I think I can rule that out. Braking seems normal and I drove it to Wendover last month (100 miles each way) and didn't experience any of that.

If a brake was dragging enough to feel less power you would definitely notice a smell when you get out of the car. You can also feel all four wheels after stopping to see if they all feel the same temp. I've had front brake hoses in daily drivers plug and the wheel is so hot you can not touch it.