Car Doctor Q&A: Were There’s Smoke, There’s a Vacuum Leak

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Engine misfires are frustratingly intermittent, and difficult to diagnose. AAA Car Doctor John Paul says that with a little bit of smoke, a mechanic might be able to diagnose the problem.

Q. I have a 2010 Honda CR-V and it has a lot of miles on it. Over the past year I have replaced the spark plugs, wires and had the fuel injectors cleaned. The problem is that from time to time the engine misfires. When it does this sometimes the check engine light will even flash. When it runs smooth it runs great. Any idea as to what the problem could be?

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A. The first thing I would do it look for an intermittent vacuum leak.

The best professional tool for this is a smoke machine. These tools pump smoke into the engine and you simply look for smoke leaking out. The leak could be a intake manifold gasket or even a vacuum hose.

You can actually buy canned smoke, believe it or not, but there are a number of videos on YouTube that describe how to make your own smoke machine and find a vacuum leak:

The other possibility is this engine is desperately in need of a valve adjustment. It is not unusual with some vehicles that over time the valves can get tight and cause a misfire. My suggestion would be to check the valve adjustment and adjust the valves as needed.