Wrong Spark Plugs?

[Broosedamoose]

According to the tech article, the plugs for a 4.0 SOHC are the Motorcraft SP-498. However, every site I go to lists them as "Does not fit your vehicle"! I don't have an owners manual and doing a search just made things so much more confusing! The Ford site list an SP-412 as the right part. Any input?

 

[RonD]

SP498 is single platinum, SP412 is Nickle, either will fit 4.0l SOHC

But you want SP500 double platinum spark plugs in your 4.0l SOHC

Ford used Waste Spark system with a 3 coil pack, 3 coils and 6 spark plugs??
This means each pair of spark plugs is wired in Series, 2 spark plugs spark at the same time, so one spark is "wasted", hence the name, Waste Spark System.
Series wiring means one spark plug will spark "normally", a center to tip spark, but the other spark plug will have "reverse" spark, a tip to center spark
Single Platinum(or other coating) is usually on the tip, with "normal" spark that's where the most wear happens.

With Waste spark this means that one bank(3 spark plugs) will wear out the same as regular copper/nickle so no real benefit using 6 single platinum spark plugs.
Double platinum(tip and center both coated) will last the same on both banks
And because some of the 4.0l SOHC spark plugs are hard to get to, longer lasting spark plugs would be better.

In some years Ford used TWO different spark plugs, single platinum tip on one bank, and single platinum center on the other
When you are buying thousands of spark plugs the cost savings is for single platinum is worth it.
And you could do the same, but for just 6 spark plugs I would do the double platinum.
Spark plug gap needs to be 0.054, a wide gap but engine won't idle well with smaller gap

This thread has pictures of the spark plug wear: https://www.ranger-forums.com/4-0l-...e-single-platinum-spark-plug-4-0-sohc-119625/

Bank 1 has tip wear
Bank 2 has center wear

Same thing happens on the 3.0l and 4.0l OHV engines using a coil pack(waste spark) system



And not that it matters, but the waste spark system was the very first spark system ever used, so nothing new
Your lawn mower and any other small engine with magneto still uses it.
Crank shaft spins 2 times for each 4-stroke cycle of a gasoline engine.
Magneto/points are driven by crank shaft
So spark timing is set for piston TDC, intake stroke or exhaust stroke, doesn't matter spark plug sparks on both, on intake stroke it ignites the air/fuel mix to keep engine running, on exhaust stroke is does nothing, doesn't hurt or help, just way way simpler to setup spark timing this way.
An no, the spark on the exhaust stroke is NOT there to "clean up" exhaust for better emissions, lol, it just doesn't hurt anything to run spark this way, just one of those Myths that float around.
Waste Spark is just simpler to use, that's why there is spark on exhaust stroke

 

[heavy breather]

So I relied on the local parts house to send me what was a factory spec plug for my 03. But they sent the wrong ones and I did not know it until after I already put them in and lost power and fuel mileage. Yes it's noticeable. So I ordered the right plugs and power has come back, have not had a chance to check mileage yet.


Sent from my iPhone using Tapatalk

 

[adsm08]

The 498 is the factory single platinum, sort of. At the factory they used two different plugs.

The 500 double platinum is the proper service replacement.

The 412 nickle plug is the acceptable "b-string" replacement if the 500s are not available.

 

[Broosedamoose]

Okay, so the SP500 it is then. The current plugs are Autolite so I know they are not original. I have an Accel coil and JBA wires from another vehicle I am going to use. Thanks for the input!

 

[RonD]

Watch the firing order on the coil pack
3 4
2 6
1 5
front

or
1 2 3
5 6 4
front

The 5 6 4 is the side I always mis-wire