Odd engine miss problem

Had a curious event happen today. The family went out to Sweet Tomatoes (salad bar buffet restaurant chain) today, my 20 year-old daughter drove the 2000 Toyota Siena van. While
getting on the highway, she floored it for about 10-15 seconds to be able to merge in front of a monster RV (greyhoud-bus class). She commented about the car "shaking" right after that. I didn't notice it at first, but soon it was more pronounced, felt like an intermittent miss. Later, it got worse, I stopped by an auto parts store on the way back home and bought a set of spark plugs, taking a wild stab at what it might be, and knowing they hadn't been changed in forever.
The rear plugs are a total bear on this car, but the internet helped me find out you take the cowl panel with the windshield wiper mechanism out to get access to the rear bank of the engine. One plug of the rear bank had the ground electrode bent all the way against the center electrode. I don't THINK I manhandled it enough to do that getting the plug out of the well and past the intake manifold, but I can't be absolutely sure of that. Obviously, the plug wasn't like that before the misbehavior, could a severe knock do that to a plug? Could a chunk of carbon have come off the piston and crunched the plug electrode? It was bent, but not totally smashed.
This car has no distributor, and has 3 spark coils. So, each coil serves two cylinders. What happens if one plug is shorted? Does that short out the other plug, too? Was the other cylinder missing intermittently, as the coil barely had enough current to make a weak spark with one plug shorted? The shorted plug was on the branch with the long plug wire, the coils are on top of the front bank plugs.
Got all the plugs back in, started it up and it ran smoothly. I didn't drive it yet, but before the work it was running so badly I thought it might leave us stranded. Unless it needs the leaner mixture for a warmed-up engine to misbehave, it sure feels like it is fixed. The check engine light came on as we were driving home, I was waiting for that to happen.
Anyway, has anyone had an experience like this, where there was very obvious ignition miss immediately after a full throttle acceleration? I've had plenty of dirty spark plugs and bad plug wires over the years, and they generally slowly got worse. I've never had a miss develop suddenly while driving. All the old plugs looked quite normal, although the gaps were all worn a bit.
Jon
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If that plug was wet with fuel or fouled when you took it out then it could have been pre-existing. If the insulator looked similar to the other plugs, then it happened as you took it out.
The most likely cause for getting a miss starting on one cylinder after a bit of hard acceleration, that then comes and goes, is that the insulation has broken down on one of the three coils. If you can access the coils and inspect them _very_ closely, you may see a small burned spot. Or you may not :-(
It'll probably only affect one cylinder, even though they are shared coils, this is because the coils are double ended, not parallel connections.
A coil swap is usually quicker than a plug swap on these modern engines :-|
HTH
Mark Rand RTFM
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I'd have to go with a chunk of *something* in the cylinder. Carbon is always a possibility, probably from the EGR system.
Could have been a piece of anything from the intake tracts, from build day or a service, waiting to get jostled just right.
Make sure it has an air filter in it.
Dave
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Jon Elson wrote:

Being a 2000 you probably had a chunk of carbon break free. I would try running a can of seafoam through it using the instructions on the can for "upper intake cleaning". Basically your going to run the engine up to temp. Then use a vacuum line to draw in the seafoam until the engine quits. Shut the key off and let it set for an hour or so. Then start it back up and drive it a bit to blow all the loose crap out.
Word of MAJOR WARNING, DO NOT DO THIS PROCEDURE IN A GARAGE OR WITH THE EXHAUST POINTING AT ANYTHING YOU WANT TO KEEP CLEAN!!!
It WILL generate a smoke cloud that will make you think the place is on fire, and the loose carbon,crud and crap that come blasting out of the exhaust is VERY sticky!!!

With that plug grounded out it would have stopped both cylinders on that coil from firing. Makes the engine S H A K E like a paint mixer...
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wrote:

No, a grounded plug on a double-ended coil affects ONLY the cyl with the damage. BOTH plugs fire at the same time, every time. With the one plug grounded, the other plug gets the full charge, just like with a coil per plug system, or a conventional distributor type system, where the "inner" end of the coil secondary is grounded.
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wrote:

And we know this how? <G>
Gunner
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Gunner Asch wrote:

SOP to warn folks. I've used it and GMs top cylinder cleaner quite a few times. There is a fine print warning on the can and some folks don't bother reading it. One friend of mine didn't pay attention to my warning and had to repaint a section of his garage wall and air it out for about 2 days.
I know of a person on a list I'm on who was actually pulled over by the police while he drove around to burn off the cleaner. They thought the car was on fire!!
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wrote:

Ok. I was just wondering if you had found this out personally.
Something Ive never done. Oh no..not me!
I did however do something similar in my last garage, when trying the "Decarbon by pouring water down the carby while racing the engine" trick.
Got the carbon out of that old truck. Sure as hell did! Worked great! I think it cleaned out 30 yrs of carbon from that old 64 Chebby. Cleaned out the muffler too!!! And the tailpipe..and the ashtray......
Only problem was..I too had to wash walls for 2 weeks to get rid of the spooge....sigh..I ultimately had to buy a couple gallons of dish soap..and marinate the walls for that shit to come loose.
It got so black in there..I had to run outside to breath. Seriously.
Gunner
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Jon Elson writes:

Something like that happens if you occasioned damage to the torque converter; it shudders from then on not unlike a missing cylinder. Of course, replacing spark plugs won't help this.
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Richard J Kinch wrote:

Well, I didn't want to declare success until the car had been driven and brought up to full engine temp, etc. I STILL don't know what the hell happened, but it must have been in the plugs. I might Ohm them out before chucking them. So, my wife drove it yesterday and said it ran perfectly fine. The funny thing is it really felt like it was missing on at least TWO cylinders, it was much more than a little rough at the end, and continuing to get worse. We restarted it twice after the initial rough running.
Jon
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My old 4 cyl Toyota PU had an intermittant rough running problem. It always happened on the road and was fine as soon as I got home. One night it happened again and I pulled off and popped the hood to see what was happening. I heard a odd tick-tick-tick like an electrical discharge but there was no visible sparking. Back at home it was running ok as usual so I pulled the plugs - all ok. Ohmed out the plug wires - all ok. I bought a new set of wires, they were cheap enough, and installed them. Ever since it has been running perfectly and my gas mileage has gone up 10% too. Art
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Jon Elson wrote:

OK, I Ohmed out the plugs, and one definitely had an open resistor. If you really leaned on the center electrode it would make intermittent contact, but otherwise was infinity Ohms. The other plugs were difficult to measure due to non-conductive deposits on the electrode, but if you poked through that, most of them seemed to read around 6 K Ohms. A couple others might also be a bit flaky, the deposits made consistent readings difficult.
So, I did find an actual defect in at least one plug. I can imagine a plug with a disintegrating resistor going fully bad after a 10-15 second full-throttle sequence.
Jon
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On Mon, 30 Aug 2010 22:19:12 -0500, Richard J Kinch

My PT cruiser has had an easy life for the last couple months, but last weekend I floored it pretty good to pass a double trailer semi on a two-lane - and it missed for the rest of the trip out (about another 10 miles) and all the way home (about 20 miles). I was going to pull the plug wires to see which cyl was missing when I got home - and low and behold, it idled PERFECTLY. Hasn't missed a beat since, so I won't worry about it unless it starts misbehaving again.
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On Tue, 31 Aug 2010 20:42:30 -0400, snipped-for-privacy@snyder.on.ca wrote:

I have, on occasion, seen a bit of carbon caught between plug electrodes. Gerry :-)} London, Canada
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snipped-for-privacy@snyder.on.ca wrote:

That sounds like the old stepvan I had. The gas tank was rusting, and some flakes made it through the fuel pump and would cut off the flow at the fuel filter if you pushed it. Shut it down, and they would drop back to the fuel pump.
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Most coil pack systems fire two plugs at once. The secondary is connected plug tip, block, block, and plug tip. Jumping the gap on the non compression plug is trivial. If shorted, even easier.
Wes
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The other thing you should do is ohm out your spark plug wires. 6-10 ohms. I've had a bad wire make my 4 cylinder Saturn do the shakes. I put an old wire on it that I saved and drove it for many miles.
Also look for arc over from boots on coil packs.
My car is about 52,000 miles since the last plug change and 70,000 since I changed the wires according to Quicken. I hope to get this corrected this weekend. I have the parts but it has been too freaking hot after work lately.
Responding made me do the research on my car. I bet my rough idle issues go away soon. :)
Wes
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On Tue, 31 Aug 2010 18:50:27 -0400, Wes

6 to 10 K ohms. Not 6-10 ohms with radio suppression wires.

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snipped-for-privacy@snyder.on.ca wrote:

Damn. You are correct. Spare keyboard, my normal one got drenched.
Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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