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Rough running engine

19,000 miles on a 2003 Ford E250 5.6L V8 engine, starts running rough, check engine light comes on, limp to mechanic, they change the spark plugs. Now it runs fine until I take it up to highway speeds and then starts running rough again but not as bad as the first time and no check engine light. Help.

What did the mechanic say the spark plugs looked like? This van should have had platinum-tipped plugs, designed to last up to 100,000 miles. With all the sitting this van does, judging by the miles, I’m worried about signs of carbon fouling. This can happen with engines used primarily for short drives.

Try using some Techron with the next fill-up. Most auto parts stores have it for about $15.00 a bottle for the big one. If the plugs went this early, there may be some deposits clogging up the fuel injectors as well.

I’m also worried about the fuel in the fuel tank. The general consensus is that modern gasoline with 10% ethanol, the most commonly available, has a shelf life of about 90 days, then it goes stale. This greatly affects it’s burn qualities and the amount harmful deposits that can form on the fuel system. When this van is parked for extended periods of time, some fuel stabilizer, like ‘Sta-Bil’, should be added to the gas tank and run through then engine to prevent ‘bad gas’ damage.

If you plan on keeping this van for a while longer, you may want to look at the maintenance schedule for other maintenance you need based on the time interval instead of the mileage interval. The coolant needs to be flushed and filled and the transmission probably needs service, just to name a few.

Thanks for your suggestions. The mechanic is checking for a bad coil on Monday. I have another vehicle that was more my daily driver for years but now that my grandson is driving it I do drive the van more but being retired and disabled, I admit I don’t drive much. I will use your suggestions and see what happens.

 That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

The check engine light only came on that one time and they changed the plugs. The CEL indicated a problem with one of the plugs so they changed them all based on the age of the van. The mechanic now thinks it might be a coil but since there is no CEL this time he’s guessing based on his experience. This guy is honest so that’s a good thing, he just is not sure what might be wrong without looking into it further. I really appreciate the help I’ve received here. I’m very undereducated about engines and am trying to learn more. Thanks.