Ford 4.2 Motorcraft Spark Plugs (Cu vs Platinum)

[nobb]

I was recently servicing a 2006 Ford Freestar and changed out the old factory plugs. I noticed one bank had plugs labelled "AGSF-34EM" and the other banks "AGSF-34EGM". Not sure what the difference between the EM and EGM is, or why different banks have these two different plugs from factory. A quick search seems to indicate these fall under the Motorcraft SP504 part #. These are both platinum plugs.

Strangely, in any part # lookup for this vehicle, and other similar Ford vehicles using the Ford 4.2 engine, the recommended plug is a Motorcraft SP506 which is a copper plug.

Does anyone know why the discrepancy? Can I just use the platinum SP504 for future services? Mainly to double the service life because the rear bank of plugs is a PITA to change on minivans so reduced servicing would be nice. Or could I even look into an iridium plug for even longer life?

Thanks!

 

[Olas]

Spark plug is a conductor. If the thread and heat range and gap are correct you're golden

 

[Lubener]

Maybe the last mechanic only changed the plugs on the easy bank and left the difficult ones alone. I would go with the Motorcraft platinum which will work on your 4.2 and run them for 75k.

 

[nobb]

These are definitely factory. This is my parents' van bought new so I know the full history.

Looking at the service records, the dealer charged them $220 @ 50,000 km for a spark plug "R and R" of which I found out is just to inspect and clean. It's easily a 2 hr job to get at the plugs, so why they wouldn't have changed out the plugs instead I don't know.

Yet another reason why I do my own work from now on.

 

[jorton]

My 99 4.2 f150 came the same way. The plugs were color coded with a drop of paint on the end of the terminal, by engine bank. NGK has an iridium plug that lasts longer than coils do, up to 200,000 miles. Look for the one that costs $12-$13 dollars(less on Rock Auto).

 

[Bluestream]

Waste spark system uses double platinum one bank single platinum on the other Bank you can replace with double Platinum if you want ...

 

[Tman220]

The reason for different plugs between the two banks of cylinders depends on whether the engine uses a waste spark ignition system. One bank will have the platinum puck on the center electrode and the other will have the platinum puck on the ground strap. The reason they did this was because on waste-spark systems (two plugs firing at the same time) one side of the coil pack will cause a spark to jump from the ground strap to center electrode, while the other side of the coil pack will cause the spark to jump from the center electrode to the ground strap.

There is a very slight wear difference to the spark plug depending on the origination of the spark but really it's nothing to write home about and why don't see the same differences in replacement spark plugs.

That might sound like a mindless exercise and probably cost ford more money to monkey around with plugs like that, but it's just the opposite! Platinum is expensive, by doing this Ford used only one platinum puck per plug and made it as small as possible because they only put it where it needed it the most to achieve emission warranty requirements. When your buying 60 million spark plugs per year it makes a difference.

update: Current cost of Platinum is almost $905.00 per ounce.

 

[nobb]

Thanks guys but are you sure the 4.2 uses a waste spark system? The SP506 is the recommended replacement plug for all cylinders, but it's a copper plug with single electrode.

 

[RF Overlord]

The answer to the question of why 2 different plugs is exactly as Tman220 said. As to whether the 4.2L is a waste-spark system I don't know...if it uses a coil pack or a pair of coil packs, then the answer is Yes. If it has COP (Coil On Plug), then No.

 

[larryinnewyork]

I noticed the same situation on my 2002 Ford Ranger
Factory Plugs changed at 99,000 miles.
(3) AGSF32PGM and (3) AGSF32PM

I bought (6) replacements AGSF32FM (Motorcraft) Platinum
Why the difference in numbers ? I don't know.
These plugs were Platinum and lasted only 37,000 miles before wearing out (.070" gap)

I replaced again using Autolite XP-104 Iridium
So far so good with 4,000 miles on them.

Also, when I changed the WIRES at 99,000 miles, I bought "aftermarket" WIRES and they also lasted 37,000 miles.
I then bought Motorcraft thru RockAuto. Like the Iridum Plugs, so far so good.

 

[slacktide_bitog]

In a transverse V6, use NGK Laser Iridium so you won't have to do them again for another 100k

 

[nobb]

Originally Posted By: larryinnewyork

These plugs were Platinum and lasted only 37,000 miles before wearing out (.070" gap)


Same thing I noticed! Changed out the OEM platinum Motorcraft plugs @ 150,000 kms and the gap was 0.070". Correct spec is around 0.054"

 

[slacktide_bitog]

Originally Posted By: slacktide_bitog
In a transverse V6, use NGK Laser Iridium so you won't have to do them again for another 100k

never mind. It seems NGK doesn't offer Laser Iridium for your Freestar, so use Denso Iridium TT instead. Part number 4713. Denso TT plugs and NGK wires (part number 52011)

 

[bdcardinal]

4.2 is waste spark. It has that coil pack with 6 plugs for the spark plug wires on top, that is waste spark. The old plugs should have had a paint mark on them indicating they were factory.

 

[Bluestream]

Originally Posted By: nobb


Strangely, in any part # lookup for this vehicle, and other similar Ford vehicles using the Ford 4.2 engine, the recommended plug is a Motorcraft SP506 which is a copper plug.

Thanks!


Where are you looking up copper core plugs? Look in the owners manual, no one would recommend copper core plugs for that engine, although you can use them if you want to change every 50,000 KM.

Left bank will wear centre electrode, right bank will wear the ground strap. Therefore: Use single plats on left bank and double plats on right bank. Or just use double plats.

 

[nobb]

Originally Posted By: Bluestream


Where are you looking up copper core plugs? Look in the owners manual, no one would recommend copper core plugs for that engine, although you can use them if you want to change every 50,000 KM.


Fordparts.com, RockAuto...they all reference the SP506 copper plug. Owner's manual does not actually give a part number. All it says is to ask the dealer.

 

[bdcardinal]

We go by VIN on the lookups for everything. I have SP-506 in stock and the box says "Nickel" nothing about Copper. Fordparts.com is not a very good source of information, have had customers come in with part numbers off of there that were wrong for their application multiple times.

 

[Bluestream]

Rockauto and others and others may list copper core, but that does not mean that's what Ford would recommend. The owner decides what to use based on many factors including how long are you going to keep and how easy are they to change.

 

[punisher]

Originally Posted By: Bluestream
Rockauto and others and others may list copper core, but that does not mean that's what Ford would recommend. The owner decides what to use based on many factors including how long are you going to keep and how easy are they to change.



Such [censored]. That difference in appearance is due to the difference in electrode diameter, not the material.

Any plug number listed on the under hood emission decal? That was usually my first go to for plug specs/part numbers.

 

[Bluestream]

Exactly! The material is only relevent for durability...A copper core plug with the same shape center electrode of a platinum or Iridium would have short life..