Car Talk Dear Car Talk:
I have a 1997 Jeep Grand Cherokee with a 6-cylinder engine and 4-wheel-drive. I never had any problems with it until recently. My wife was driving down the road at about 50 mph, and it started missing then blew the muffler off. I took it to a mechanic, and he did a diagnostic test that showed nothing wrong. He put another muffler on it, and about two weeks later, it did the same thing!
I took it to the Chrysler dealer and they said it wasn’t showing any codes, except about every few minutes, an oxygen sensor code would show. They put two oxygen sensors on it and charged me $300. Two weeks later, it blew another muffler. We even tried it without the catalytic converter, and it still blew off the muffler.
This has happened four times so far (four mufflers). Do you have any suggestions? I can’t give up -- I love this car! — John
It sounds like you’ve got a bad backfire. When the spark gets interrupted, some of the raw gasoline that doesn’t get burned will end up in the exhaust system. And then, when the spark returns, combustion can take place in the exhaust system in addition to the cylinders.
That explosion of unburned gasoline inside your exhaust system is what’s blowing off your mufflers,
John. So your mechanic needs to figure out what’s interrupting your spark.
My first guess would be something called the crank angle sensor. The crank angle sensor does a lot of things, including directing the spark to the right cylinder at the right time. And we’ve seen bad crank angle sensors in a lot of older Jeeps. They tend to act up when the engine is hot.
It could also be a wiring problem, a bad coil, bad rotor or a bad distributor pickup. But I’d start with a crank angle sensor. That’ll cost you a hundred bucks or so, including installation. Good luck, John.
Dear Car Talk:
I have a 2013 Toyota Prius V hybrid with 68,000 miles that I love. It has been trouble-free. It has hauled me, my dog and all our gear on many fun vacations for five-plus years and constantly gets 45 mpg. However, now that I’m pushing 70, I’d like to get out of a tent but still travel economically. I found just the thing — a motorcycle