Need Help Troubleshooting Misfire on 99 4Runner

Hi all. I'm having a bit of a difficult time tracking down the cause of a misfire on cyl #4 in my 4Runner. So far I've moved the coil to see if the code follows it; it didn't. So I replaced the spark plug and got the same misfire and code. Then I realized that I needed a dual electrode plug so I replaced it again. (Only cost $3.50 for the first plug so I'll consider that a cheap lesson.) Got the same stumble and code on the way home. Wires are NGKs and are like two years old with maybe 10k on them. Truck has the 3.4l with 202k on the clock. Thoughts?

EDIT: I did get a code for a cyl 3 misfire and a random misfire before I moved the coil. The code has been confined to cyl 4 since then. It's also not consistent. I drove to the store last night to return a movie and my rig ran fine.

Is it "coil on plug"?

If it were older with a dizzy, I'd SWEAR this was a bad wire shorting to ground...

In reply to Hungary Bill:

Halfway. The passenger side cylinders are COP and then there's wires going from those coils to the corresponding cylinder across the motor. Cylinders 1, 3, 5 are COP and 2, 4, 6 are not.

IIIIInteresting. might want to give the wires a gander then. Maybe run the engine when it's dark out and see if you can see spark jumping. In the daylight you can look for areas of rubbing on the wires (chaff marks etc)

Yeah, weird right?

The wires should be new enough but you know how that goes. Good idea on looking for arcing tonight. I'll try tonight and see what happens.

Those really skinny wires right? Don't let them touch anything, they are not well insulated. I once had one short out to a washer hose of all things, like flashing CEL misfire bad.

With that type of 1 coil 2 plug set up you can't always trust that it's giving you the right cyl number for it's misfire code. The opposite plug and it's wire are equally suspect. If the coil attaches directly to one one of the plug boots remember that there is a conductor in that boot that can fail too.

In reply to HappyAndy: The coil does plug directly into a plug. Wouldn't switching the coil help isolate that conductor going bad?

Or do I need to pony up another $3.50 for a spark plug for cyl #3?

If the variables were only "plug and wire" (and I think right now they are) the order of moving stuff could go like this:

Swap #3-4 wire with another wire (if possible), run engine. If problem persists you MIGHT be "good enough" swapping #1 plug with #3 plug and re-evaluating. ($aves ya three-fitty) I'll add in the caveat that the engine has to be faulting to be troubleshot. If it's running fine, then there's no use in swapping stuff or looking for arcing (I'm sure you know this, I'm just covering bases).

For those interested: two plugs, one coil = wasted spark system

https://en.wikipedia.org/wiki/Wasted_spark

Here's the paired cylinders. Noticed I was wrong when my rig ran like garbage after pairing 3&4. Oops.

I can't swap wires between them (not enough length) so I guess that means I'm buying new ones? I hate to just throw parts at it but I don't know what else to do. I've switched plugs and coils now and am still getting the code.

Could be a bad injector. Just had a coworker with a 1997 4Runner that was missing borrow my OBDII scanner. He got 2 codes for misfire and couldn't isolate what the problem was. He could smell unburnt fuel in the exhaust, and didn't want to just throw parts at it (which probably wouldn't have solved the problem as we were discussing ignition causes as the most likely problem). Wound up taking it to the dealer and they cleaned all the injectors and found one that was bad. After the cleaning and new injector he is running fine.

In reply to secretariata: That doesn't sound good. How would I test for a bad injector?

If you eliminate the usual misfire suspects, Check for a clogged catalyst. I've seen weird random misfire/low power condition on this gen high mileage 4 runners a couple times now. Spin the primary o2 out of the offending side and remove. Drive it. Will be stupid loud, but run normally.

Well, I just replaced the plug wires. $80 later, I have a smoother idle and the same misfire code. Guess it's off to the dealer for an injector service?