Hello everyone, I greatly appreciate any help I can get.

I have a 1999 ford ranger with a 4.0L engine with 160K miles. I've had the truck about 7 years now. Since I've owned the truck it's always had a shaking problem. After owning it for a year or 2 I discovered all I had to do was change out the #3 spark plug because it was getting oil on it, by the electrode where the spark is generated and on the threads. The plug wire end is clean. This worked up until about a week ago. I was the driving the truck real hard, flooring it for a good 15 seconds here and there. Then when I parked, the shake was back. Next morning I bought a new plug, it didn't fix anything. I bought all new plugs and wires still didn't fix anything. I used my video camera on phone to look down the spark plug whole and there appears to be a good amount of sludge on half of the #3 piston. There isnt any smoke coming out the exhaust. A friend of mine says it could be a motor mount causing the misfire. Any help is greatly appreciated, driving a shaky truck sucks lol

 

Motor mount causing a misfire, LOL.


Normally the 4.0 suffers from crappy intake gaskets and cracked heads causing the rough idle.

Oil fouling can be from bad rings or bad valve seals, either way you need a compression check to verify that cylinder is still holding pressure.

 

Oil on the plug usually means bad oil control rings on the piston. Part of the top is clean beacause the plug is igniting the oil. You may not be noticing any smoke out the tailpipe because the #3 may be your only problem and there just isn't enough smoke volume to notice. The question is why would only that piston be affected? I am guessing you might find similar piston tops on the other 5 pistons. If not, I'd look at the valves in the #3 piston. The only sure thing is that it isn't the engine mount. Good luck.

 

I had a similar problem with my '99 Ranger 4.0L. It developed a jerking/surging action when going past 40 miles per hour. The Check Engine Light (CEL) came on and the code I got from my OBDII indicated a P0304 (misfire in #4 cyclinder). I Inspected the plug and the wiring to the coil pack and everything seemed to look OK. However when I swapped the #4 plug with the one in #5 cylinder, the CEL code indicated misfire in #5 cylinder indicating that the #4 plug was defective. I replaced it and that corrected the problem. One thing to check is the connector to the coil pack. Also the possibility that you may have "hairline" crack/s in the head which often does not present any immediate problem but overtime could cause the adjacent plug to misfire. The sludge build up in the cylinder could cause the plug to foul up and could also indicate bad oil or compression rings. Get a compression check on this cylinder and also make sure that all your fuel injectors are OK.