Okay... so I got a weird one. Brief history. Thru a code for a bad O2 sensor left bank upstream. I was just starting a long 1600 mile run. replaced Both upstream after the run. Computer reset all good no more codes. Started throwing misfire on #3, #5 and #7. Plugs and wires are less than 2 years old. decided to replace coil packs as they were original and at 122k made sense. Codes cleared. Started a highway run, misfire codes on #3 and #5. Called my mechanic we talked and decided to throw in a bottle of injector cleaner. finished highway run with no new codes...... Now I can run all day long with no problem as long as I stay under 50 MPH. as soon as I go over 50 -55 I throw misfire on #3 and #5. I go back under 50 and nothing.
Anyone have any thoughts. besides never driving over 50.
And in the mean time Wishing all a Merry Christmas.

 

What are the exact fault code numbers you are getting?
When was it last tuned with new 8 mm silicone wires?

 

mike the codes are P1300, p1303, p1305. the wires and plugs were changed in January of 2011

 

Have you pulled those plugs to inspect them? 3,5
Have you looked under the hood in complete darkness yet it helps to identify a loose spark.

 

lr... I pulled the plugs all looked okay?? no difference in color etc from any of the others I pulled all 8 to cross check. Have not tried to look at night. will see what I can do over the weekend.

 

You could have a small nick or burn on those spark plug wires but that you would think would leave a constant misfire.

 

Agreed I checked the wires for any visual signs of damage, pinched anything but nothing. The only over 50 -55 thing is just bizarre, but then again it is a rover so I guess nothing is really bizarre.