My 2003 Mazda B3000 was missing just a little when cold and running at low rpm. I went to an online vendor and bought NGK standard plugs and a plug wire set and ignition module reccomended by the vendor. Not premium stuff, with shipping it probably ran right about $75. I installed all parts this afternoon and my test drive has me feeling that I have solved the problem. The plugs I removed were Motorcraft platinum and the gap on all of them were close to .070. The center electrodes look slightly rounded but otherwise these plugs look pretty good. They were the plugs that were in the truck when I bought it, currently 59k on the odometer . Could such a large gap on the plugs have caused the rough running? Thanks in advance, G

 

Yes, the gaps were too wide
2003 Ranger 3.0l specs 0.042 to 0.046, 0.044 is the popular choice

You can check the EMISSIONS sticker under the hood, it should have spark plug info
I have seen some stickers with .052-.056 which is correct for the 4.0l engines

Also read of gaps as large as 0.065, can't see this as being correct

Maybe previous owner never gapped the new plugs and they came with 0.065 and are now .070

I would set at 0.044

 

I set the gap on the new plugs at .044. The missing at low rpm is gone. One other thing that is gone, at least for now, is the bucking that I experienced at around 45 mph if I accelerated slowly. Initially I thought it was a tranny problem but I had read on this forum that it might be a tune up problem and apparently that is correct.