Josh's Engine is Misfiring and He's Got Questions.

Dear Car Talk

Dear Car Talk | Sep 29, 2015

Dear Car Talk:

I have a 2002 Lexus ES 300. The mechanic says that I have three cylinders misfiring in "bank 1." I don't know what to do. He sounds like he just wants money. He said it will be $90 an hour just to find out what's making them misfire. The car is shaking, and the Check Engine light is blinking. What does it mean that cylinders are misfiring? And what is bank 1?

-- Josh

Bank One was the name of that ballpark in Phoenix before they changed the name to "The Bank That Ate Bank One Ballpark."

Actually, in automotive terms, a bank is a set of cylinders. So, because you have a V-6 engine, you have two banks of three cylinders each. Those banks form a "V" shape. That's why they call it, what? A V-6!

And "misfiring" just means that a cylinder is not firing every time it's supposed to. Each cylinder in your engine is supposed to fire (that is, combust the fuel and air, and push the piston down) every other time the crankshaft turns. If a cylinder doesn't fire every time it's supposed to, it's said to be misfiring.

That makes the engine run rough and the car shake.

And if you have three out of six cylinders that are badly misfiring, the car will barely run at all.

In this car, as in many cars, the engine is installed transversely (aka sideways), so bank 1 is the cylinder bank closest to the passenger compartment.

That makes it hard to reach, and requires removing other parts to get at it.

So one possibility is that your spark plugs never got changed back there. Maybe you went in for a tune-up and some lazy mechanic had a hard time removing the pieces that are in the way of those plugs.

He scraped his knuckles a few times, gave up, tossed the new spark plugs in his toolbox and said, "OK, pal, you're all set."

That would be a nice, easy solution. Those plugs should last 100,000 miles. But if the plugs in bank 1 have been in there for 150,000, while the plugs in bank 2 were changed at some point, that could cause your misfiring.

It also could be the coils. Each cylinder has a coil that generates the spark needed for the cylinder to fire. Those can go bad, too.

Or you could have a crack in an intake manifold gasket, creating a big vacuum leak. That would cause very rough idling and misfiring. If it is a vacuum leak, those symptoms should disappear when you run the car at high speed. So if you can drive it on the highway with no misfiring and adequate power, that suggests a vacuum leak.

But if the Check Engine light is flashing, you need to take care of this right away. That flashing light is warning you that the catalytic converter is being damaged. Your injectors are working, sending fuel into the cylinders, but the fuel isn't getting combusted. Instead, the unburned fuel is going right through the cylinders into the exhaust system, where it's ruining your catalytic converter. And that's many hundreds of dollars.

So if you don't trust this particular mechanic, you need to find one you do trust, Josh. Someone needs to figure this out for you. You might check www.cartalk.com/mechanics-files. That's a database of trusted and beloved mechanics, compiled by our own readers and radio listeners. You put in your ZIP code and read the love letters about shops in your area.

But don't panic and freeze up, Josh. It's going to cost you some money to diagnose and fix this, but not fixing it will cost you even more. Good luck.


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