Q: We have a 2003 Nissan Murano with 102,000 miles that we purchased new. Three times in the past year the car suddenly started running extremely rough. The engine jerked and bucked for 5 to 10 minutes. While this was happening, the “service engine soon” light was blinking on and off, but it has never once recorded or stored a fault code. Each time this happened, we pulled over, turned the car off and let it sit for a few minutes. When we restarted the car, it ran just fine again.

The first time this happened, the dealership ran a diagnostic but couldn’t find anything. They recommended the 90,000-mile scheduled maintenance, which included new plugs, wires and a tuneup. I did this and thought the problem was solved. But it has happened two more times since then. Without a specific fault code, I really hate to take it to the dealership and have them start replacing parts in attempt to find the problem.

A: Typically, the flashing “check engine/service engine soon” light points toward multiple misfires and a significant amount of excess unburned fuel reaching the catalytic converter — enough to potentially damage the converter. With no fault codes stored, start with a back-pressure test of the exhaust system to determine if the converter may be clogged or the exhaust system restricted. This test involves removing the front oxygen sensor, installing a pressure gauge and running the engine. More than about 2 pounds per square inch back-pressure could indicate some type of restriction.

The intermittent nature of your misfire might also point to a possible ignition problem. Since you had new plugs and wires installed, the coil packs may be suspect. Also, my Alldata database pulled up a Nissan recall in 2003 that called for upgraded crankshaft and camshaft position sensors in certain Nissan engines from that year.

It might be worth checking with the dealership to see if your vehicle was included and whether the updated parts have been installed.

Q: A lot of water got in my 1998 GMC Jimmy’s gas tank. I drained the tank and pumped out the water. It will run if I pour gas in the throttle body but quits when I stop pouring gas in. It will not stay running.

A: Can you hear the fuel pump run for 2 seconds when you first turn the key to the “on” position before cranking the engine? If not, check its relay. Also, look for a green unconnected wire near the driver’s side inner fender that is used to prime the fuel injection at the factory.

It’s possible to apply battery voltage to this wire — make sure you identify the correct wire! — to test-operate the fuel pump. And, finally, debris may be clogging the sock filter on the fuel pickup inside the tank.