Has anyone had trouble with the standard motorcraft plug AGSF42fm running
hot. I have a new engine in a 97 150 only 9000 miles on it. It seems to have
trouble starting and the plugs look burned. I was going to replace them with autolite platimun they list ap765 plugs which are obviously the wrong plug.
agsf has a .708 thread length and the ap765 only has .489. Is there a substitute plug for the motorcraft listed plug? Or does anyone know what the corredt autolite plug is? Anyone have this problem?

 

Hmmm...
Not sure about the '97 but the 2000 I had used Motorcarft AGSF34EEM. (which I believe is the functional equal of the AGSF34FM)
I have also used Autolite and Champion copper plugs with very good results.
I checked Motorcraftparts.com and Advance Auto's and Autozone's website.
Looks like the 42FM is the plug called for for the '97.
AA and AZ sites do list equivalent plugs in the Champion and Autolite lines.
I do suggest you stay away from anything other than Motorcraft, or Champion or Autolite.
Too may folks have had bad luck with Bosch and maybe Denso and/or NGK.

Let me do some looking through some old posts.
I'll be back.......


edit: OK, I'm back. Nothing new to report. Seems you have the correct plugs. Did you look at the sticker under the hood to see what is called for?

If nothing else, try a set of Autolite copper plugs, and I'd speculate the gap would be .054 on the '97, but verify. Also, make sure the plug length and thread length are the same


FWIW, the general concensus is change the plugs while the engine is cold and use some antisieze on the plug threads.

One last thing, since the engine is not original, I wonder if it needs the newer speced. plugs?

 

Brian is correct;the heads might be a newer version then the 97s and call for a different plug application number.
Ide advise not using anything but Motorcraft!