Engine starts to misfire?

I have had my ranger to a Ford Dealer and other mechanics and cannot seem to solve the problem that my pickup misses when I drive it. I have changed the mass air flow sensor, spark plugs, and yesterday had a new catalytic converter put in, but it still has the same problem. Someone told me that the distributor cap has a "chip" or "sensor" in it that could be causing this problem. Can you give me more information where this item is located and if it could be an easy and possible fix for this problem? Thanks

Ford dealer should have checked the ECM for code 2 or 3 years ago and "no" the check engine light is not coming on.

This truck was running hot so I put a new radiator and thermostat in it. The Check engine light indicated that 2 and 6 was misfiring so I put new plugs and wires and new intake gaskets. The Check engine light went out. Drove it for 1 and 1/2 weeks and the light is back on saying 2 and 6 has misfire. What Could be going on now?Do you think when it was running hot that the head gasket needs to be replaced or could it be the valves?

Engine Performance problem
1999 Ford Ranger 6 cyl Two Wheel Drive Automatic

well we have a 1999 ranger witha 4.0 v6 that just wont run smooth, I checked to see what cylinders it was missing on, it infact was missing on the #3, #4and#6 cylinders I rplaced plugs and wires the coil pack is sparking strong this leaves me to believe that it is maybe a timing issue, I have made sure that the firing order is right, I pulled each plug wire off one at a time to find with ones didnt make a diffrence hince the missing cylinders I just cant pipoint what the problem is any help would be great

Recently, while I was out of town, there was a problem with my 1999 Ranger. My teenage son was driving it and it started running rough. Since I wasn't home, my wife dropped it off at a local repair shop. They thought they knew the problem immediately, found a loose or broken connector on the coil pack. Then they said it was the coil pack, then an injector. They went through several items but continued to get a misfire on #6 detected. They finally gave up, only charged for some of the work that they did. Their diagnosis was probably a small crack somewhere in the engine, and would be more expensive to repair than to just replace the engine. Said to just baby it around, it would be reliable for what it is being used for. I was skeptical of diagnosis. When I got home I noticed that after a short trip, it started running hot. I stopped and checked the water, and it was dry in the reservoir. Added antifreeze to the system and monitored. The temperature dropped after a little bit but required turning on the defroster/heater. Started looking at the thermostat and water pump. No obvious signs of failure on the water pump. The thermostat appeared to be stuck so I replaced it, along with a new sensor. Everything seemed to be running fine. Then the check engine light came on. Misfire on #6. I looked at the plug, went ahead and replaced it, just to eliminate it. Drove around several miles, when I checked it had the same misfire. Started doing some swaps between 5 and 6, got the expected response on the code reader. I knew that the #6 cylinder had a new injector, so I checked the wiring. Found a nick on a wire going to number six, but was unsure if I caused it or already there. Repaired it so far no misfire. Now all I get is sometimes the exhaust looks like white smoke, other times nothing. Sometimes the truck will run hot, and have to switch heat on to lower the temp. No obvious signs of water in the oil. Any further suggestions?
Randy

It is the temperature of the vehicle. We do smell coolant occasionally through the heater/defroster, not always. I will check again, but it appears that the coolant system is holding pressure. Haven't looked at the transmission fluid yet.

I had a message of a misfire on my number 1 cylinder and thought it was old plug wires. I got a tune up replacing wires and plugs and took it home and then eng. Light came back on and same message came up. Firestone looked at it for the day and said I have a bent valve. I have been driving it for a month now after that and the engine light will come on and off and the truck will run smooth then run rough at times. Does this sound like a bent valve? If it was bent would it not be doing it all of the time?

Ok, long story short: 3 mos ago, I changed plugs n wires, during the swap, one of the new plugs ceramincs got cracked, so I used one of the old plugs that was still in almost new condition. about a month later, I get random bogging down, no torque, mostly during acceleration, but then started getting worse to where it could happen if on the highway passing someone. so I decided to start small and replace the 1 plug that was from the old batch. bought a new plug, put it in and the truck was acting really bad, like it was running on 5 cyl. so I took the new plug out and made sure it was seated properly, and not damaged. put back in, same thing. removed it again and put old plug back in, no change. but since it was getting really late, I could just detect spark coming from the cap on the plug. thought it was the wire, tried 4 different ones, same thing. this morning, took the plug out and the end had a decent amount of carbon buildup and from the threads to the igniter was really burnt pretty good. (see image) also noticed the ceramic now was cracked, put the new one back in, and the sparking from the plug cap went away, but still runs like on 5 cylinders.
completely at a loss.

No ticking or knocking, I will try and get a compression test in the next day or two.
Sorry, forgot to mention this is the 3.0L engine.

Ive been told by several other people it could be a clogged cat? Since the truck does have almost 170k and its the original cat (Im guessing as I bought it used) this sounds plausible?
Still waiting on the mechanic to be able to get me in for a compression test.