Thinking back to when I changed the spark plugs - one of them had a crack in the porcelain. I replaced the plugs, but didn't replace the coils til 2 weeks later.

Could the bad coil have caused the new spark plug to already go bad (and thus, arc, even though I changed the coil 2 weeks later)? I'm going to check it out tomorrow when I get the truck back.

Ok so it looks like you have an automatic.

This thing is missing when driving but never at idle.

Does it miss fire in every gear?

I guess it would be helpful to start understanding the load when this occurs... and also to rule out torque converter clutch issues.

Edit 2: how does your engine coolant look? Any signs of the transmission cooler leaking?

fixer said:

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Ok so it looks like you have an automatic.

This thing is missing when driving but never at idle.

Does it miss fire in every gear?

I guess it would be helpful to start understanding the load when this occurs... and also to rule out torque converter clutch issues.

Edit 2: how does your engine coolant look? Any signs of the transmission cooler leaking?

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No leaks. Seems to misfire in every gear.

Transmission cooler will leak into engine coolant...

Is the miss fire worse under heavy acceleration or light acceleration?

fixer said:

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Transmission cooler will leak into engine coolant...

Is the miss fire worse under heavy acceleration or light acceleration?

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Same all the time.

I'm wondering if your engine is really misfiring at all. Hard to tell through a message board.

If it was a "dead" misfire you'd have codes set. If it was a "lean" misfire you'd have codes set for random misfire as well as fuel trim. If it were cam timing you'd have a host of codes set.

Next time it happens, see if you can get the same sensation in park/neutral by moving rpms up to 4k. If you do get it then it may be a fan clutch with a bearing going out. I had a Ram 5.9 that had a fan clutch with a failed bearing and it would randomly get lodged/wedged into an off-concentric position and cause a vibration that felt like a mis fire or torque converter issue. I was able to get it to repeat at idle after a long run and the element had heat soaked.

If not then its clear you have to have tires rotating to make the sensation occur. Then it might be a driveline issue like u-joints, center drive shaft carrier, transmission mount, possibly engine mount.

Is this thing 4wd? I've noticed that when front bearings are failed in front ADD diffs on Toyotas, they can make a misfire sensation if the failure is bad enough. This occurs right on tip in throttle like at stop light or stop sign.

It's 4wd, but I've already replaced all the bearings.

Including the needle bearings in the differential?

fixer said:

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Including the needle bearings in the differential?

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I had the entire rear differential replaced about 9 months ago.

Front differential

Misfire still randomly occurring. I've got an ODB sensor hooked up with real time data. The truck has misfired twice during the time I've been scanning, but it pulled no code and I can't see any issue electronically.

I'm going to try taking it to another mechanic. I have also had the fuel injectors cleaned.

Haven't read the thread but did you also change the cap and rotor?

Ragoo said:

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Haven't read the thread but did you also change the cap and rotor?

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Surely you jest

Ag for Life said:

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Ragoo said:

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Haven't read the thread but did you also change the cap and rotor?

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Surely you jest

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idk, I may be dumb

Couple remaining sources if its truly an engine misfire.

Could be the O2 sensors, could be something with the fuel trim management system, could be the air intake having a sticking point.

zooguy96 said:

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Misfire still randomly occurring. I've got an ODB sensor hooked up with real time data. The truck has misfired twice during the time I've been scanning, but it pulled no code and I can't see any issue electronically.

I'm going to try taking it to another mechanic. I have also had the fuel injectors cleaned.

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When the misfire occurs, is it a short burst or period of misfires then the condition goes away?

fixer said:

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zooguy96 said:

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Misfire still randomly occurring. I've got an ODB sensor hooked up with real time data. The truck has misfired twice during the time I've been scanning, but it pulled no code and I can't see any issue electronically.

I'm going to try taking it to another mechanic. I have also had the fuel injectors cleaned.

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When the misfire occurs, is it a short burst or period of misfires then the condition goes away?

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Single

Ok. I would have someone inspect driveline for mounts and u joints. A single misfire is a bit strange given how much you've put into secondary ignition and injectors.

fixer said:

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Ok. I would have someone inspect driveline for mounts and u joints. A single misfire is a bit strange given how much you've put into secondary ignition and injectors.

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Ok, i will. Thanks. .