Ford 4.2L Spark Plug Part # Confusion & Heat Rating

[nobb]

I'm servicing a 2006 Freestar with the 4.2 engine. The spark plugs that came OEM on this engine was a Motorcraft SP504 platinum (AGSF34FM). The manual and online part# only reference a copper plug, the SP506 (AGSF34N).

Strangely, for older model Freestars (2004-2005) with the exact same 4.2 engine, they reference a Motorcraft platinum SP486 (AGSF42FM).

Based on this spark plug decoder, it seems the newer SP504 is just a colder heat range plug:
http://jimsprojectgarage.weebly.com/motorcraft-spark-plug-information.html

So does anyone know why Ford changed the recommended spark plug part # for 2006 on the exact same engine? Why did the plugs that came factory on this engine (SP504) not even come up as a choice?

I just put in the older higher heat range plug, the SP486 and just want to make sure ir's ok. It's a HUGE PITA to do plugs on this van.

 

[WyrTwister]

Have they quit making them ? Maybe had problems with them ?

 

[nobb]

Originally Posted by WyrTwister
Have they quit making them ? Maybe had problems with them ?


Nope all plugs are readily available on RockAuto. Basically for the exact same 4.2 engine they changed the recommended spark plug part # in 2006:

2004 - 2005: SP486 (AGSF42FM)
2006 - 2007: SP504 (AGSF34FM)

 

[atikovi]

Maybe ask Motorcraft directly?

 

[StevieC]

The could have changed something in the engine management system and require cooler running plugs. Could also have found pre-ignition was happening and decided on a cooler plug in later years. I've seen this before, not just with Ford but with other OE's. Same engine but different spec plugs from year to year.

 

[Number_35]

Originally Posted by nobb
I'm servicing a 2006 Freestar with the 4.2 engine.

It's a HUGE PITA to do plugs on this van.
I haven't worked on a 4.2, but have done (some of) the plugs in a Ford 3.8 in a Windstar, which was the Freestar's predecessor. Is the 4.2 an OHC engine? The 3.8 is an older pushrod engine. The front bank is not bad. The plugs in the rear bank are a real pain. They also tend to seize into the AL heads. I wasn't able to change them all because I was afraid of stripping the threads in my friend's van. (Mine, I might have taken a chance.)

 

[WyrTwister]

Last time I changed plugs on anything was a FWD GM V-6 . The rear bank , next to the fire wall was ha huge pain . One of the things I had to do was to remove the front " bog bone " & use a 2 x 4 to pry the engine forward , to gain more space between the engine & fire wall ! :-(

Front bank was not that bad .

 

[Kruse]

IIRC, the factory manual says you need to have real long and real skinny arms to get at the back spark plugs. I found this impossible, even though I have about a 7'5" wing span. I had to take apart the wiper assembly to access these.

 

[nobb]

Yea it's the rear bank that's the pain. Have to remove a bunch of plastic covers first like the windshield cowl then crawl ontop of the engine and reach in there. Everything is done by feel so you have to be super careful. Which really sucks because when you try to put in the plug, you're banging it all over the place so you just try your best not to get dirt in there. I think I've read about some people being able to access the rear bank from the bottom but I've never tried.

I put in the SP486 (AGSF42FM), which seems to only be referenced for the older model year of Freestar. Everything seems to be running fine, no signs of pre-detonation from the hotter plug. I just want to make sure it's ok to leave these plugs in.

 

[Wagonmaster261]

Originally Posted by Number_35
Originally Posted by nobb
I'm servicing a 2006 Freestar with the 4.2 engine.

It's a HUGE PITA to do plugs on this van.
I haven't worked on a 4.2, but have done (some of) the plugs in a Ford 3.8 in a Windstar, which was the Freestar's predecessor. Is the 4.2 an OHC engine? The 3.8 is an older pushrod engine. The front bank is not bad. The plugs in the rear bank are a real pain. They also tend to seize into the AL heads. I wasn't able to change them all because I was afraid of stripping the threads in my friend's van. (Mine, I might have taken a chance.)

The 4.2 is a bored out 3.8. Still OHV. Similar engines used in F150s and vans, but oriented properly.

To do many things on a Windstar/Freestar, the wiper cowl needs to come off. Still better than an Aerostar...