News spark plug thread size is different from old one

[serg011]

I was about to change the spark plugs on my Explorer Sport 96, V6.

After I removed first plug and comapred with one that dealer sold to me (AGSF42FM) I found that the thread is much longer on the new one comapring to the old one:

Bigger picture

I'm lost at this point. Is it OK and I just put the new one in, or I need to bring them back and get something new?

Also the old plug doesn't look that bad at all to me. Do I really need to repalce it? I have 60,000 mi on it and recently bought it from private party when it was 58,000.

Thanks,
Sergei

 

[Howard]

I would say that you've got the wrong plugs there. Don't fit them as you may do damage to the piston crown. Take em back together with an existing plug and try again. Or if your old plugs are ok get your money back.

 

[Doug904]

Actually you need to look at your emissions label on the front core support on your Explorer. If it says AGSF42FM's then that's what you need to use. It looks like the other plug you had in there was a aftermarket brand by some other name. The prefix AGSF on the spark plugs is what most all of the OHV 4.0's use. The number is the heat range. The Sufix is the type of plug, example platinum, copper or iridium.

later Doug904.

 

[Howard]

These are the part numbers my Haynes manual says

1991-1993 AWSF-42C
1994-1995 AWSF-42PP
1996-ON AGSF-22PP

With a gap of 0.054 inch

Hope that helps. You may be able to read the number on the old plugs and see if it matches any of those.

 

[serg011]

It's interesting:

1. The plugs that are in the engine now are Autolite APP765

2. The emission label says AWSF42PP

3. The plugs that dealer sold to me: AGSF42FM

No match at all

It seems the previous owner changed them already.

But why the thread is so short? Is it supposed to be like that? I checked the picture on the Kragen website and thread looks full length there.

I don't think I would be able to fit plugs I bought, even dealer claims that despite the number changed the plugs are the same.
h

 

[Doug904]

According to the Motorcraft website the AGSF42 and AWSF42 plugs will both work with that year 4.0. Now the suffix of FM stands for Fine Wire Platinum where as the factorys had PP or double platinum. Bottom line is they are fine and the correct plugs for your application. Only in the later model SOHC's are the aftermarkets having problems designating the correct spark plugs. Gap them at .048-.052 to help the idle a bit and to give the ignition system a little help.

I run AGSF12FM's on all of my supercharged 4.0's and recommend them to all of my customers.

Looking at the pics you posted it looks like the aftermarket plugs saved a few dollars by not threading them all the way up. The sealing ring is still in the same place on the plugs, yet another reason to buy Motorcraft.

Later Doug904.

 

[95exploder817]

when i did my plug change on my ohv the autoparts store gave me a mixture i had some with the short thread and the others had the long tread and the old plug on the x had the short thread so over all i should not go with the long thread plug