4.0 Spark Plug Recommendation

It came with Autolite platinum's. So that would be a safe bet.

I can tell you my experience. I bought Bosch Platinum +4's and put in my 92

4.0 Ranger back when I had it. The truck then had something around 90k miles. Then I was single and couldn't care less about the cost of the parts; I just wanted the best. It ran ok on the +4's, but not very smooth.

About 20k miles later, I replaced the +4's with Autolite double platinums and there was an immediate improvement. The truck never really ran right with the Bosch's in it. A friend who was both a Ranger owner and pro mechanic (he's worked for both Chevy and Ford dealers) told me that the 4.0 Rangers just seemed to run better on the Autolite APP's. He was absolutely right.

If you're getting them, I think you need the double platinums. IIRC, some of the plugs receive a positive charge from the coil pack, some receive a negative charge. This influences the direction of the spark across the gap. In the factory plugs, some have the platinum on the center electrode, some have it on the ground electrode. You'll either need to get Motorcraft plugs identical to the originals and install them in the exact same cylinders as the originals, or you can get the Autolite APP's.

That's just anecdotal, I know. Hope it helps some.

CJB