Random Multiple Misfire on all cylinders

[Schurkey]

So I’ve narrowed it down to it being cylinder 2.

HOW did you "narrow it down"?

From your scan tool photos, it looks like all the cylinders (1--6 shown) have occasional misfire.

I swapped around spark plugs and wires to be sure it didn’t follow and it did not.

Kinda surprised that with all the parts you replaced, plug wires weren't among them.

I did notice the spark plug was slightly covered in oil, figured it could be seals. Could the seals cause it to misfire?

If the valve stem seals are fouling plugs, sure. But from your description it doesn't sound like the plugs are getting that fouled.

It’s very intermittent.

That makes it harder to track down.

Also when above 1K rpms there are no misfires whatsoever.

Vacuum leaks have the greatest effect on smoothness at lower RPM.

I’ve confirmed many times with a smoke leak machine that I have no vac leaks.

Are you sure? A vacuum leak into the crankcase (problem with the underside of intake gasket) would be harder to spot with a smoke machine.

Explain this photo:

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Is this showing extremely-slow activity of the two main O2 sensors? Is the scale at the bottom showing 41 seconds...42 seconds...43 seconds, and so forth? Or is that 41 milliseconds, 42 milliseconds, etc?

 

[AuroraGirl]

HOW did you "narrow it down"?

From your scan tool photos, it looks like all the cylinders (1--6 shown) have occasional misfire.


Kinda surprised that with all the parts you replaced, plug wires weren't among them.


If the valve stem seals are fouling plugs, sure. But from your description it doesn't sound like the plugs are getting that fouled.


That makes it harder to track down.


Vacuum leaks have the greatest effect on smoothness at lower RPM.


Are you sure? A vacuum leak into the crankcase (problem with the underside of intake gasket) would be harder to spot with a smoke machine.

Explain this photo:

You must be registered for see images attach

Is this showing extremely-slow activity of the two main O2 sensors? Is the scale at the bottom showing 41 seconds...42 seconds...43 seconds, and so forth? Or is that 41 milliseconds, 42 milliseconds, etc?

That scan graph is slower since the X axis wasnt touched on the zoom, if you zoom it in the lines would be bigger. OP you can full screen that graph on the O2 sensors and it will actually refresh faster and with more more frequency (You dont need it for this post tho)

Id say potential distributor issues

 

[docstoy]

I see that you have replaced distributor, if you were to mount a dial indicator to measure distributor shaft up and down motion, and how many minutes or hours of run time on oil treatment additive to help with possible seal issue ?

 

[Papikev252]

HOW did you "narrow it down"?

From your scan tool photos, it looks like all the cylinders (1--6 shown) have occasional misfire.


Kinda surprised that with all the parts you replaced, plug wires weren't among them.


If the valve stem seals are fouling plugs, sure. But from your description it doesn't sound like the plugs are getting that fouled.


That makes it harder to track down.


Vacuum leaks have the greatest effect on smoothness at lower RPM.


Are you sure? A vacuum leak into the crankcase (problem with the underside of intake gasket) would be harder to spot with a smoke machine.

Explain this photo:

You must be registered for see images attach

Is this showing extremely-slow activity of the two main O2 sensors? Is the scale at the bottom showing 41 seconds...42 seconds...43 seconds, and so forth? Or is that 41 milliseconds, 42 milliseconds, etc?

Hello Shurkey and sorry for the late reply.

So I had replaced the plugs and wires on whim and now my data only shows misfires mainly on #2 and every now and then on #7. I know they’re next to each other on the firing order so I thought maybe sometimes the main misfire on #2 was sometimes causing it on #7.

I’ve also replaced the lower intake gaskets twice to be sure, and I even followed your advice on previous posts with using gasket sealer around coolant passages and gasket maker on the China walls.

O2 sensor readings are good now that I’ve learned the zoom method as well.

 

[Papikev252]

I see that you have replaced distributor, if you were to mount a dial indicator to measure distributor shaft up and down motion, and how many minutes or hours of run time on oil treatment additive to help with possible seal issue ?

I replaced it a while back but with an O’Reillys brand. It’s an aluminum one. I can also get a dial indicator to check the shaft movement, i just didn’t think to do this since it was new but i know new parts can still be bad, but i have pulled it to double check the gear and it seemed to be okay but I haven’t checked shaft play.

 

[Papikev252]

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This is the new misfire data since plugs and wires were replaced with AC Delco. I also did another injector balance test to be sure and they all have the same amount leakage when activated and looking at a fuel gauge. I’ve been reading the manuals a lot and see they have a “enhanced ignition diagnosis” process and was going to try that out.

 

[AuroraGirl]

You must be registered for see images attach

This is the new misfire data since plugs and wires were replaced with AC Delco. I also did another injector balance test to be sure and they all have the same amount leakage when activated and looking at a fuel gauge. I’ve been reading the manuals a lot and see they have a “enhanced ignition diagnosis” process and was going to try that out.

how quickly does that 20 add up? is it like 20 seconds, 1 second?

It being one cylinder makes it a little easier because you know it cant be something that affects all equally. Remove your cap, is there any evidence that is behaving strange inside the cap to the post? Maybe its broken off the plastic and pushed away?

 

[Papikev252]

how quickly does that 20 add up? is it like 20 seconds, 1 second?

It being one cylinder makes it a little easier because you know it cant be something that affects all equally. Remove your cap, is there any evidence that is behaving strange inside the cap to the post? Maybe its broken off the plastic and pushed away?

Yes it’s like 20 within 20 seconds I could say, it doesn’t count very fast. Most of the time it doesn’t reach even 6 and resets to 0 , but It never goes out of 20s.

I’ll double check I just put a new AC cap, I have an extra laying around too I could check.

 

[Papikev252]

Yes it’s like 20 within 20 seconds I could say, it doesn’t count very fast. Most of the time it doesn’t reach even 6 and resets to 0 , but It never goes out of 20s.

I’ll double check I just put a new AC cap, I have an extra laying around too I could check.

I also used to get the P0300 but I don’t anymore since replacing plugs, just that slight misfire so that’s good.

 

[AuroraGirl]

Yes it’s like 20 within 20 seconds I could say, it doesn’t count very fast. Most of the time it doesn’t reach even 6 and resets to 0 , but It never goes out of 20s.

I’ll double check I just put a new AC cap, I have an extra laying around too I could check.

so youre misfire is infrequent enough to be below threshold now, whcih to me sounds like a cylinder specific thing since it improved with other repairs. Swap plug with nearby cylinder, and/or wire and recheck