Hello, new here and asking obo my daughter who has an 03 F150 Sport with the 4.2L V6. She had always complained about poor mileage despite having overdrive and when I pulled the plugs at 46,000 miles the gap was around .060 and they were Motorcraft OE? Platinums but this is the mystery. On the left bank the plugs were AGSF 34EM and the other bank has AGSF 34EGM. Motorcraft's website doesn't list either part number but does list AGSF34FMF6 or 34C as the correct plug.

First Q is this, is there a heat range difference in these plugs? What (is) the difference? I'm assuming they are the factory plugs.
In any event, why the poor mileage? Hopefully the new plugs, Autolite 5144s will make a difference gapped at .044 but I'd still like to know why her motor had two different plugs in it?
Motorcraft's website and info number couldn't help and referred me to my nearest Ford Truck dealer and their service and parts mgr couldn't help me either.
Thanks for any information you can provide.

 

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Thread moved to 4.2L V6 engine forum.

See ya on the boards!

-Matt

 

If I remember correctly, one side is single platinum and the other is double platinum when you pull the stock plugs. Mine was the same way on my 2000. The Ford parts guy I talked to didn't know what I was talking about either when I asked why he gave me 6 of the same plugs.

I do remember this being addressed in an old thread. You might find it doing a search in this forum.

Isn't .044 a little close? I thought the rec. gap was .052-.056? Just curious?

Rich
2000 XL 4.2 5spd 127,XXX miles
Not running as of this this evenings commute home
SES on for the first time, so I can't complain too much...yet

 

jakerin,
Welcome to FTE and the 4.2 forum. Glad you found us and hope you visit often!
What you found with the two different plugs is normal. (for the OEM factory plugs)
One side is a single platinum and the other side is double platinum.
If I remember correctly, this is due to the polarity of the voltage sent to the 2 different banks (+/- vs -/+). I know the answer is somewhere at FTE, but it's been so long I can;t remember excatly where I found it.
Anyways......
If you had gone with platinum plugs for replacements they would have been double platinum. But, it looks like you went with what I did in my previous (2000) 4.2:

https://www.ford-trucks.com/forums/s...ht=spark+plugs

The Autolite copper plugs worked fine and were way cheaper than platinum plugs.
Don't neglect the wires, but 46,000 might be a bit early to need replacement.

What is her MPG? City and hiway?
There tends to be a fairly wide variation when it comes to MPG. I tend to think the single biggest factor is how hard the truck is driven. I can easily vary my mpg by 2-3 mpg depending on how I drive it.

You can use the "search" feature to search this forum for more info on both spark plugs and MPG.
There are plenty of old threads here with all sorts of info.

Again, glad to have you here.

edit: I do seem to remember gap being around .050. I think the sticker on the fan shroud indicates the proper spark plug gap.

 

Thanks guys. I'll be checking her mileage as time goes by. I still don't understand why double platinums are installed on one cylinder bank and not the other??? And, why replacing them shows no indication of this 'factory' preference. Its running fine so we'll see how and if the mileage improves.

 

When manufactured, many Ford engines were assembled with single-plat plugs on one side. The double plats (or fine-wires) were needed on the other side of the coil's polarity due to the opposite polarity of the spark in the waste fire system. Using the single plats where they were sufficient to operate correctly saved a little money on every car or truck that Ford built. Over the entire production run, the cost savings were significant. Ford used this same strategy for most of their engines with waste-fire systems.

Replacements are done with either double plats or finewires, eliminating the need to stock and to install two different plugs when changing them. At the retail level, the cost per job is not significant.

Fine-wires, while a single plat design, eliminate the need for a double plat and replace both the singla and double plat conventional design.

Steve

 

"Replacements are done with either double plats or finewires,"


So, is there anything wrong with replacing them with Autolite 5144s? They aren't platinums much less double plats.

 

The Autolite copper plugs will work fine. I used them, as have quite a few others.
I understand the reason for platinum is to provide longer replacement intervals.
The coppoer plugs will not last as long but are easliy replaced and cheap.
I'd figure 20-25,000 miles or so for the copper plugs.