I developed a misfire this evening. It's done it once or twice a few months ago, but only for a second or two then it was gone. Now it seems more perminant. It runs fairly well when at a constant rpm, but under load it misfires pretty bad....especially at low RPM. It's a 2001 4.2 XLT with Mac air intake, electric fans and about 75K on it. The fuel filter is about 9 months old. I think plugs and wires are original, but I'm not the first owner so can't be sure. No warning lights and no codes.

My idea is to start with the fuel filter and work through the plugs and wires. I know some people say to check the fuel pressure. Can I do that myself?

Update: I checked for codes again and it says there is a cylinder 1 misfire, but no Check Engine Light. And which cylinder is 1.

 

Cylinder 1 is the front one on the passenger side. This a top view.
4 1
5 2
6 3

 

Sounds almost exactly like what I'm trying to track down.. Good luck. No lights on mine either.

Chickenboy, how did you pull your own code? Reader?

 

It ended up being the plugs. Replaced them and it ran fine. It actually runs better. It's had a small stumble at idle since I bought it and the new plugs cleared it right up. Maybe a plug going bad from day 1.

WVF150....I've got a code reader I bought for my wife's car a while back. Although you can go to the parts store and have it done for free most of the time, it comes in handy. It saved me a headache when the Check Engine Light came on and I found it to be an O2 sensor unplugged.