OT, But I need the best minds

[Marty]

OK we have a 98 Ford Ranger with a 4 liter mill in the family stable. After about 10k miles the #1 cyl plug starts to miss, the OBC2 codes are all clear except for #1 ignition miss. When I pull the plug it looks good no damage to the electrode, insulator or ground electrode, but the plug will not spark. This has happened 3 times always at 10k miles and I can't figure out how or why the same plug keeps failing repetedly. The wires are new also. Has anybody ever seen anything like this????? Its freaking me out. After 40 years around cars iI've never even heard of this sh#t going on and I'm stumped.

[Velocewest]

Have you swapped the plug to another hole? They can fail internally, and if it's intermittent it could happen due to heat. How about swapping plug wires to be sure there's not a bad wire? Even new sets sometimes have faults.

Does the car have a distributor or multi-coil pack? Those coils can die on one side, we found that in my nephew's Olds minivan.

[Mike Self]

was recently posted here? If the cylinder is running lean, the plug could get very hot and cook internally but still appear to be OK. Try running a resistance test on the bad plug, and then on a plug from another cylinder that's working OK and see what the Ohmeter says.

And as was previously stated, try the plug in another cylinder and see if it works there. Also with the plug out and connected, lay it on the valve cover while someone cranks the engine and see if it sparks.

Finally, do a compression test on the cylinder, and compare it with the others--see if there's an anomaly...

Let us know what you find. This is indeed puzzling.

mike

[Marty]

Ok I changed the plug today and all is running well again. The plug I pulled has a resistence of 8.5k ohms from top to electrode and is a nice brown color about like the icon here for unread areas of the forum it also reads 1.5m ohms between the top and the ground electrode. The new plug reads 4.9k ohms from the top to the elctrode and 2.9 m ohms from top to ground electrode. I did replace the #1 wire after the second plug change and it made no difference.