Strange spark plug wear.

[Chris142]

The 6 sparkplugs in my jeep wear odd. It has a waste spark system and I don't know if that matters.

It does not matter what brand of plugs I use although autolite were the worst. Cyl 2-4-5 open up the gaps quickly.

The plugs are to be gapped @.035 and yes I gapped them.

Currant ngk plugs have about 7000 miles on them. 2-4-5 were @0.45. 1-3-6 were still
035.

Why would those 3 plugs open the gap up so much so quickly? The plugs do not seem to be worn at all. Just bigger gaps.

As mentioned it's always done this and plug brand does not matter much with the exception of autolite that were .080 on those 3 cyls.

 

[clinebarger]

Not unusual for waste spark system to wear half the plugs unevenly, Guess something to do with the reverse polarity?

 

[ctechbob]

Cline beat me to it.

Waste Spark Ignitions - NGK Spark Plugs

If you drive a car from the 1980s, be aware of the waste spark ignition and what that could mean when you are purchasing replacement spark plugs.

ngksparkplugs.com

"It is important to know that in a waste spark ignition system that spark plug electrode wear occurs differently based on the polarity. For plugs in a positive polarity position, more electrode wear will occur at the ground electrode. Plugs in a negative polarity position will experience more wear at the center electrode.

As a result of this, vehicles equipped with waste spark ignitions often use double precious metal spark plugs, such as the OE Iridium® or OE Platinum®. These dual precious metal plugs feature either iridium or platinum on the center-firing electrode and platinum on the ground electrode. Because these electrode materials are harder, gap erosion is reduced, allowing for a longer service interval. Since these materials are denser, this will reduce gap erosion, thus leading to a much longer service interval. The use of nickel-alloy or single precious metal spark plugs in vehicles equipped with waste spark ignitions will result in more aggressive gap erosion and shorter spark plug life."

 

[Snagglefoot]

Very common for the plugs to open up more on one bank the other on a waste spark system. My 2005 Taurus with the 3.0 Vulcan did that with its factory Motorcraft plugs.

 

[Chris142]

Cline beat me to it.

Waste Spark Ignitions - NGK Spark Plugs

If you drive a car from the 1980s, be aware of the waste spark ignition and what that could mean when you are purchasing replacement spark plugs.

ngksparkplugs.com

"It is important to know that in a waste spark ignition system that spark plug electrode wear occurs differently based on the polarity. For plugs in a positive polarity position, more electrode wear will occur at the ground electrode. Plugs in a negative polarity position will experience more wear at the center electrode.

As a result of this, vehicles equipped with waste spark ignitions often use double precious metal spark plugs, such as the OE Iridium® or OE Platinum®. These dual precious metal plugs feature either iridium or platinum on the center-firing electrode and platinum on the ground electrode. Because these electrode materials are harder, gap erosion is reduced, allowing for a longer service interval. Since these materials are denser, this will reduce gap erosion, thus leading to a much longer service interval. The use of nickel-alloy or single precious metal spark plugs in vehicles equipped with waste spark ignitions will result in more aggressive gap erosion and shorter spark plug life."

The oem plugs are copper champions. These jeeps are known to be very picky when it comes to plugs. A single platinum plug will cause misfires.

Btw the autolite that were the worst were # APP985 which is a double platinum plug.

 

[mk378]

Some people rotate them like tires so the other half of the plugs run with reverse polarity for the second half of their lives. This is actually practical if you can just switch wires at the coil pack instead of unscrewing plugs.