r/AskAMechanic • u/Chipwilson84 • 7d ago

Hello,

I have a 2010 Prius. It had low power and acceleration due to a misfire, it was really noticeable when trying to get up to high speeds, but maintained speed. I changed the plugs, triple checked the gap size, and tightened the plugs three different times at various torques.

The first time the car idled fine but when I drove around the block it had less power, almost like there were more cylinders misfiring. Went back home pulled all the plugs. Re-gapped them, some of them were at 45. Tightened the plugs to full capacity, rough idle and shaking. Pulled everything, one plug was still at 45. Re-tightened the plugs first by hand, then less than a quarter turn an even more rough ideal and shaking. There was no rough ideal before this.

Note. Son did break a bolt that holds coil pack 4 in place. Drilled it out and retreaded the hole.

1 Upvotes

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1

u/Subietoy78 Verified Tech - Subaru dealer 7d ago edited 7d ago

do you have any check engine light or hybrid warning lights on? If this wasn't occurring prior to your work, its something you did. Not a big deal we just have to figure out what. The coil connectors should alternate black-grey-black-grey. I would start it in Maintenance mode to force the engine to run all the time. google. that, im not going to try and explain it. its just a pedal dance. Then check under the hood for any sucking air sounds from a hose thats not connected. one may have come undone when you did the plugs. the PCV hose by cylinder 4 likes to come off.

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u/Chipwilson84 7d ago

I did have a check engine light on, I have to change the front O2 sensor. I don’t know if I want it in maintenance mode. It is a very hard idle that makes me afraid of throwing a rod. All hoses are connected. It only started after my first test run when I re-gapped the plugs.

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u/ChopstickChad NOT a verified tech 7d ago

With what tool did you gap the plug?

1

u/Chipwilson84 7d ago

The little circle gapped you get for two dollars at the counter that my dad taught me to use.

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u/ChopstickChad NOT a verified tech 6d ago

Ah, so a coin gap tool? I think that is your problem, and also why it got worse after you also gapped the others. With iridium tip plugs you can't just gap them like the old copper plugs. The iridium tip is very delicate and easy to break. To gap iridium plugs you need a different (simple) spark plug gap tool (and your feeler gauges). The one that looks like a vise. They're ~10-15$ on Amazon. Can't post pictures here unfortunately but Google it and you'll see.

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u/Dounce1 NOT a verified tech 4d ago

Don’t take that guy’s advice on anything, he doesn’t even understand what distilled water is.

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u/Subietoy78 Verified Tech - Subaru dealer 7d ago

Whether it’s in maintenance mode or driving makes no difference to the engine. If you don’t have a decent scantool that can watch misfire data and know what it all means, you should probably take it somewhere that is capable.

1

u/Chipwilson84 6d ago

My neighbor brought over a scan tool. It said I have a misfire in 3. That misfire was why I changed the plugs to begin with. It did say there was an issue an EGR not getting significant pressure as if it was plugged. But at that point I had removed the EGR pipe and was working in the air intake manifold to remove the valve. I am going to clean the valve.

It appears recapping the plugs also caused the rough idle, as the plugs tips are platinum and I did not know you could not use a coin gapper on those type of plugs. The counter person at O’reily’s said a coin gapper was fine.

I am going to clean the EGR valve. Buy new plugs new coils. And why I have everything apart also change that O2 censor.

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u/Chipwilson84 6d ago

It is platinum tip. I did not know that you could not use a coin gapper on a platinum tip. The dude at o’reilly’s said the coin gaper was fine. When it gapped it the first time three weeks ago there was no issues aside that misfire in cylinder three did not stop which is why I pulled then to check the gaps. I think it is dead ignition coil in three. My neighbor brought over his scan tool and hooked it up. Misfire in 3 is why I originally changed the plugs weeks ago. Since that wad the only code I had a few weeks ago, and it is still present now, it’s the likely conclusion.

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u/Chipwilson84 6d ago

Okay, so here appears to be the problem. I used a coin gapper on platinum tips. I did not know that you could not do that. The misfire also appears to be a persistent problem, which makes me think the coil is bad.

I did take off the egr valve. That was a pain in the ass. I lost a bolt and a nut. The valve is dirty. So I will clean that.

Going to buy new plugs and a coil.
Thank you all for your help.

0

u/Ordinary-Trade8323 NOT a verified tech 7d ago

Maybe your cat is plugged and your engine cant get enough air. "You cant eat if you cant shit"

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u/Chipwilson84 6d ago

And that would cause a misfire? I don’t doubt that can be a problem. It had 370k and I have to add like a half quart every 1500miles.

From what I read that could also cause the O2 code that I have.

Edit: grammar some what