Two Different Plugs in my 4.0?? - Ranger-Forums - The Ultimate Ford Ranger Resource


4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 10-06-2008
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Two Different Plugs in my 4.0??

I am the original owner of my 2004 Ranger and last night I changed the plugs for the first time (99,000 miles). I noticed that cylinders 4,5,&6 had AGSF24PM plugs while cylinders 1,2,&3 had AGSF24PGM. Anyone know why there would be two different plugs in the engine? I assume they are very similiar, maybe a different temperature???

I put in AGSF24FM all the way around. I used a .054" gap as that is what the sticker under the hood says, although the haynes manual says .061-.068.
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Old 10-06-2008
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Its a money saver by ford. The two sides of the engines use the plugs differently. One side needs the platinum on the electrode side, the other side of the engine needs the platinum on the tip side (my terminology is off, but you get the point). The solution is to get a double platinum plug where both surfaces get platinum. Ford saves money by saving platinum on one part of the plug.

It seems pretty cheap but I guess it all adds up.
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Old 10-06-2008
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do you have any idea why they need platinum on different sides for the motor?
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Old 10-06-2008
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I don't understand it myself but it has to do with the coil packs. The electricty flows differently for one bank over the other.
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Old 10-06-2008
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Originally Posted by quicksilver2001 View Post
do you have any idea why they need platinum on different sides for the motor?
Due to the way the coil pack is configured , the current that produces the spark on one side flows from the center electrode to ground , while the opposite side flows from engine ground to the center electrode.By useing platinum on the electrode from which the spark is originating less metal burnoff is realised.Thus prolonging the life of the plug.
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Old 10-06-2008
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Ford was able to tailor the platinum on the factory-installed plugs to the coil polarity and save a small amount on each plug which adds up to something significant in a manufacturing situation. Replacement plugs are supplied with platinum on both electrodes - since they are all the same, it guarantees that the plugs cannot be installed in the wrong bank.
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Old 10-06-2008
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Originally Posted by graniteguy View Post
I don't understand it myself but it has to do with the coil packs. The electricty flows differently for one bank over the other.
Waste spark ignition, its a crappy system and it plays with Dynos (it said i had 360 ft. lbs of torque)

anyways, it sparks and then the electricity travels through the block to the spark plug on the other bank and up to the coil pack if i remember correctly
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Old 10-06-2008
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looks like it got answered. i dod a search and found this:

Always check the plug gap and condition as they come out. This can give you great insight in to what is going on in each cylinder. The gap difference is easy: EEC-V.

The "left" and "right" banks are FROM THE DRIVERS SEAT. This is very confusing, so most people use "drivers/Passenger" or Bank 1/Bank 2.

Bank 1 = 1,2,3 these are on the PASSENGER SIDE (right of driver) and are ALL Positive fire cylinders that fire fron the plug center electrode to the ground strap (...to the head and then to ground)

Bank 2 is 4,5,6 these are on the DRIVERS SIDE (left of driver) and are ALL Negative fire cylinders that fire from the (ground to the head...) ground strap to the center electrode.

This is why each side wears differently and Ford used to have two separate platinum plugs, bank 1 with the platinum button on the electrode tip (positive fire) and bank 2 with the platinum button on the ground side (negative fire) to limit erosion of the electrode as the plug fires.

This was a MAJOR nightmare as 99% of the mechanics/consumers had no idea there was a difference and the confussion was incredible. Ford went to a "double platinum" (at increased cost) to lessen the confussion.

If you look at the pictures, this is pretty obvious with the shape of the center electrode and the gap differences (but I believe they are backwards?). The positive fire plugs have the heat building up inthe insulator (normal) and the gap stays (relatively) true. The Negative fire plugs build heat in the ground strap and since it has no way to disipate this heat, the gap steadily increases until it causes misfires (cooling!) and there the gap stays.

This is why I say the 100K plug interval is a load of guano. 50K is more like it with 75K showing OBVIOUS signs of failure on my '98 Explorer (same system and firing order).
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Old 10-06-2008
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Quote:
Originally Posted by graniteguy View Post
looks like it got answered. i dod a search and found this:

Always check the plug gap and condition as they come out. This can give you great insight in to what is going on in each cylinder. The gap difference is easy: EEC-V.

The "left" and "right" banks are FROM THE DRIVERS SEAT. This is very confusing, so most people use "drivers/Passenger" or Bank 1/Bank 2.

Bank 1 = 1,2,3 these are on the PASSENGER SIDE (right of driver) and are ALL Positive fire cylinders that fire fron the plug center electrode to the ground strap (...to the head and then to ground)

Bank 2 is 4,5,6 these are on the DRIVERS SIDE (left of driver) and are ALL Negative fire cylinders that fire from the (ground to the head...) ground strap to the center electrode.

This is why each side wears differently and Ford used to have two separate platinum plugs, bank 1 with the platinum button on the electrode tip (positive fire) and bank 2 with the platinum button on the ground side (negative fire) to limit erosion of the electrode as the plug fires.

This was a MAJOR nightmare as 99% of the mechanics/consumers had no idea there was a difference and the confussion was incredible. Ford went to a "double platinum" (at increased cost) to lessen the confussion.

If you look at the pictures, this is pretty obvious with the shape of the center electrode and the gap differences (but I believe they are backwards?). The positive fire plugs have the heat building up inthe insulator (normal) and the gap stays (relatively) true. The Negative fire plugs build heat in the ground strap and since it has no way to disipate this heat, the gap steadily increases until it causes misfires (cooling!) and there the gap stays.

This is why I say the 100K plug interval is a load of guano. 50K is more like it with 75K showing OBVIOUS signs of failure on my '98 Explorer (same system and firing order).
Not true, which electrode that erodes is due to the spark polarity(as in +/- voltage), NOT due to heat. I did this schematic sometime ago that shows the spark polarity from the coil pack secondary windings. There is also no GROUND reference to the coilpack secondary windings, the engine block just completes the series circuit between the two plugs:



In addition to the opposite polarity spark, with two plugs firing in series, they also fire every revolution of the crank, instead of every other revolution of the crank as with a conventional ignition system. This is because the plugs fire just before TDC on the compression stroke, and just before TDC on the
Exhaust stroke.

Last edited by Takeda; 10-06-2008 at 05:58 PM.
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Old 10-06-2008
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The wear pattern above completely matches what I pulled out of the engine. 1,2,3 looked pretty good. 4,5,6 were very worn on the grounding strap. Thanks for the info!
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