Spark plug change at what mileage?

Hello. On a 4.0 V-6 at what mileage have you or recommened changing the spark plugs? I am coming up on 20k on my truck and a guy I work with had to change his at 25k because it started mis-firing. His plugs looked like crap when he pulled them out. Very dark and burnt looking. So was wondering if i should plan on doing this soon. Seems that is very low mileage for a change.

 

30,000 miles like Chris said but does this other guy's car have a carburetor? It sounds like something isn't right.

 

I've got a first gen and did the first plug change at 150,000 km the plugs looked pretty good for the mileage, it wasn't missing or anything but after the change the idle was nice and smooth and acel was nice and smooth too. If you are changing plugs like your buddy there something is up unless he's towing or beating the shit out of his truck. Just my opinion

 

RTM lol

 

Manual says 30k miles. I did mine at 40k miles and they didn't look terrible.

 

i bought my truck with over 80K, ran great, changed the plugs myself, and they were the original plugs in there.

 

but i would go with the 30K interval

 

Thanks for the replies. My friends isnt carburated. He has a 2008 4 liter. i think he may abuse his more than i do mine. I did see in the manual where it said to change them.

 

I changed my son's out last weekend, 105,000 MI. Gap was .065.
I ordered the plugs off Amazon, saved a few bucks on each plug and no travel time. Delivered in about 4 days.I would say you are safe to go 40K on originals unless you are having an issue.

 

does it make a big deal if the gap is larger than it should be (.04)? or has worn down? or is it just fine until it's gone?

 

thanks, do you happen to know roughly where .065 rates on operational usage, like can it go to .08, or is it getting close? and i'm just referring to the oem plugs.

 

Maybe I'll pull mine and look to see how they are...I've got 80,000Kms on her (50,000 miles).... 2006 4.0 v6.

I'm not having any miss or any issues, but I guess I should chenk 'em.

Toodles..