I have a 98 ford ranger with the 4.0L OHV V6 with 140,000k on the truck, and there is a random misfire on one of the cylinders when you put a substantial amount of stress on the engine. Almost all of the engine sensors have been replaced, the spark plugs are fine, spark-plug wires are not worn or frayed, the MAF has been cleaned, and I have replaced the fuel filter as well as had an engine compression test done and the valves are all running within 1lb. of each other. What do you think the cause of this might be?

 

Plugs and wires. Replace them. Just because they're not frayed doesn't mean they aren't bad. And your eyes can't see a crack that would be big enough to cause engine problems. Don't ever assume the obvious is good when it comes to working on cars. Also if your cylinders are within 1 pound of each other you might want to check your gauge. You're allowed about 25% difference from one cylinder to the other because there's usually always about a 20 pound spread over the cylinders from high to low. If you replace plugs and wires and it's still doing it, I'd look for something like a weak valve spring which won't show up in a compression test unless the valve isn't closing, or worn out valve seats etc. Hope this helps.

 

i replaced the plugs with bausch +4's figuring if that didnt solve it then nothing would and it worked quite well i now have all of my performance mods on