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
RAY: John, what brand of mufflers are you buying? I want to buy stock in the company.
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 creates what astronomers call the “Big Bang.” Except it’s not a theory. 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. But not including your next muffler. Good luck, John.
Towing with a Prius is possible, but at your own risk
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 camping trailer that weighs about 300 pounds.
However, my owner’s manual says absolutely NOT to tow with this vehicle. This trailer does not weigh more than two people in the back seat, so I wonder, Can I do it anyway? And now that we are headed (hopefully) to a lot more EVs in the future, can we never tow with a car again? -- Emilie
RAY: This is a very controversial issue, Emilie. More heated than whether pineapple ever belongs on pizza.
Toyota says they do not recommend towing anything with the Prius. That means that if you go ahead and tow something anyway, and you have an engine, battery or transmission problem under warranty, they can legally pretend they never met you.
I believe the issue is that by adding weight and reducing the car’s aerodynamics with a trailer, you’re going to make the drivetrain work harder than it’s supposed to. In the worst-case scenario, it’d be like constantly driving up a mountain with an entire bowling team in the back seat. And if you do that, you risk running down the battery pack and overheating the main electric motor-generator and the differential.
It’s not that you will overheat those parts. It’s that you could. And Toyota is concerned enough about it to wash their hands of responsibility if you do.
Now, if you’re a risk taker, you could decide to take a calculated risk and try it anyway. To tamp down your risk, for instance, let’s say an average small trailer weighs 1,000 or 1,500 pounds. You could decide to tow much less than that. Like 300 pounds.
And you could decide to never drive over 55 mph while towing (the engine works harder and the wind resistance goes way up the faster you drive). And you could avoid climbing mountains while towing.
And you could further reduce your risk by always having your credit card with you, so if you melt your 2013 Prius, you could hitchhike to the nearest Toyota dealer and put a down payment on a 2022.
So it’s up to you, Emilie. It’s not recommended. There is risk. At the same time, we know that some people do it and seem to get away with it.
And by the way, there will no problem in the future towing things with electric vehicles. There are already hybrid and electric trucks that tow plenty of weight. The Ford F-150 Hybrid can tow 12,000 pounds. And there are electric semi tractors in the works that can tow full shipping containers of Tombstone frozen pizza.
So this warning appears to be specific to the Prius, whose drivetrain is minimized in order to maximize its mileage. It simply wasn’t designed to tow. So tow (carefully) at your own risk.
Got a question about cars? Write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.
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