I was driving on the freeway at 70mph when my 2001 F150's 4.7l started missing. The jerks were quite noticeable. Then, when going up a hill the "service engine soon" light came on. When going down a hill it seemed to run ok and the light went out. When I got on side streets at slower speeds the engine was running really rough. I re-seated the gas cap, no change. It has just over 55K miles on it. A few weeks ago I had a single exhaust flow master series 70 installed. Unfortunately, I don't have the device to read the codes. Any help would be much appreciated?

 

You've developed a miss...you probably are going to have to change some spark plugs. Depending on how many miles, and whether you have replaced any plugs yet, you might just go ahead and replace all of them.

You could also have a bad COP, but start with the spark plugs.

BTW, you can get the codes read by places like autozone or advanced auto...they will do it for free. This should tell you which cylinder is misfiring.

 

If it's a miss it's a really bad one. At slow speeds and idle it's running so rough I thought for sure it was going to die. But you guys know better than I do so I'll check the spark plugs.

 

Just take the truck to autozone and plug it in. They'll tell you what's wrong with it.

 

I got a tank of bad gas at a small station by Bar Harbor Maine. It missed very bad on a pull and good at idle. I was pulling a travel trailer at the time. A few cans of dry gas and injector cleaner later all ok. Just need to change fuel filter again.