I'm looking for new plugs and I have found that the sites offer gaps of .044 and .040. What is the correct gap for my engine? 2003 4.2 naturally aspirated.

Also what brand would you suggest?

If they're the NGK IFR5N10 I believe they come pregapped.

JTIS says: 1.3-1.45mm (0.051-0.057in) for gap.

but you forgot to say that is for the 2.5L/3.0L V6 while the OP has listed a 2003 4.2L in his sig.

from the specifications book:

for both NA and SC starting from VIN A30645:

4.2 liter All AJ8 4575 (iridium) 0.9 – 1.0 (0.035 – 0.039)

big difference in gap

Correct you are.

Well this is interesting because the plugs that I have found on every site I visited has the gaps at either .044 and .040! Hmmmmmmm....so I would have to re-gap what I buy.

did you notice that the difference between 0.039 and 0.040 is 0.001?

it's just rounding when they converted from metric to imperial

Ok so I would need 0.040 because 0.044 is to much?

What gap are they at now? I've never heard of a plug that's reliably 'pre-gapped' no different than a tire that runs at a pressure set by it's manufacturer irrespective of the intended vehicle.

My experience is that both NGK and Denso iridium plugs come properly gapped right out of the box. That's a good thing because given how tiny the plug components are, you really do not want to be bending them....

All of the NGKs I installed on our STR last year were spot on gap wise right out of the box.

Cooper

Just changed spark plugs on my 2003 V8 after 105k miles on the original (NGK IFR5N10). The new plugs are NGK BKR5EIX-11. Did not touch factory gap at all; they work great.

.040 is correct!

"Ok so I would need 0.040 because 0.044 is to much?"

Not really - the .002 is so tiny, I wouldn't worry about it - IMHO.

This should give you what you need

Link http://www.jagrepair.com/images/Auto...sb_09_2003.pdf

Also do yourself a favor always check the gap.