Spark Plug Question

[almostclueless]

Measuring the end to end plug wire resistance will tell you if the center conductor is continuous. It will not, however, tell you if the insulation has
broken down, causing spark leakage to GND, which will also cause a misfire.

Yup. I only use good plug wires and replace them after a few years.

 

[Bob Ayers]

Yup. I only use good plug wires and replace them after a few years.

The plug wires become brittle from heat over time, and in a lot of cases, they will be damaged when they are removed from the old plugs. They will develop misfires after they are installed on new plugs

 

[fixizin]

Perhaps, but misfires are easily detected by the EDIS and reported by the PCM. And wouldn't the breakdown phenomenon you describe be visible as blue-arcing at night?

Also the wires are deliberately made with several k-ohms resistance to dampen EMI with the radio, PCM, and other electronics. It's a trade-off not made on racing engines. Apparently this resistance increases with aging to a point where it reduces spark performance, hence the directive to replace wires if MORE than 7k ohms per running ft.

That is one screwy dual-fire system, and I'm not clear what is gained by sparking the exhaust gasses... is it a re-burn/emissions thing?

Also not clear on "opposite polarity" spark? The cylinder head and spark plug threads are GROUND... are you saying that while one electrode is charged with high POS voltage, the other has high NEG voltage? And that the EFFECTS of the spark generated occur at only one electrode, and that's where the platinum is used, to counter pitting, etc.??

Those FoMoCo guys, what will they think of next... and how much will it COST me?... lol.

 

[Bob Ayers]

Also not clear on "opposite polarity" spark? The cylinder head and spark plug threads are GROUND... are you saying that while one electrode is charged with high POS voltage, the other has high NEG voltage? And that the EFFECTS of the spark generated occur at only one electrode, and that's where the platinum is used, to counter pitting, etc.??

Those FoMoCo guys, what will they think of next... and how much will it COST me?... lol.

Yes, the engine block is GROUND from the battery's reference, but as you can see from the secondaries of the coilpack, the block is just used to complete the series circuit between the two plugs firing together. So, one plug will receive a high negative voltage, the other plug will receive a high positive voltage. The electrode (ground or center) that erodes is determined by the polarity.

 

[almostclueless]

Perhaps, but misfires are easily detected by the EDIS and reported by the PCM. And wouldn't the breakdown phenomenon you describe be visible as blue-arcing at night?

Also the wires are deliberately made with several k-ohms resistance to dampen EMI with the radio, PCM, and other electronics. It's a trade-off not made on racing engines. Apparently this resistance increases with aging to a point where it reduces spark performance, hence the directive to replace wires if MORE than 7k ohms per running ft.

That is one screwy dual-fire system, and I'm not clear what is gained by sparking the exhaust gasses... is it a re-burn/emissions thing?

Also not clear on "opposite polarity" spark? The cylinder head and spark plug threads are GROUND... are you saying that while one electrode is charged with high POS voltage, the other has high NEG voltage? And that the EFFECTS of the spark generated occur at only one electrode, and that's where the platinum is used, to counter pitting, etc.??

Those FoMoCo guys, what will they think of next... and how much will it COST me?... lol.

There is spark energy leakage long before visible corona.

Race efforts can afford well shielded and grounded electronics....it isn't cost effective on mass produced vehicles.

The benefit of wasted spark is that only three coil drivers are necessary....and each coil can handle firing two cylinders in terms of saturation time just fine.

Ground completes the secondary coil path.

 

[thegoat4]

You don't know what you are talking about. Not all boots are the same, and not all engines are the same.

Once you relieve the pressure so the boot will slide down over the plug and stay on, it then creates a vacuum in some cases if you try to pull the boot back off, more especially if the boot is new.

When you have pressure to overcome when replacing the boot back over the plug, I have found that too much grease was used. If it will form pressure, it will form vacuum. I have done this several times, so I damn well know what I am saying. If you had any hands on experience other than your own vehicle I would give your advice some credibility, but since you don't....... For some insane reason you think you are some kind of spark plug guru, but I for one am not impressed. shady

A hard hard hard vacuum the likes of which you'll find in deep space is still less than 15psi trying to hold that boot on. That boot is less than 1/4 of one square inch area against that terminal. So, you're telling us that the 3-4 pounds of extra force generated by this vacuum will make it significantly harder to pull the wires?

Wires do get stuck, but your theory does not explain it.

Me, I use lots of grease. I work on more than my own vehicle. I've had to remove wires I'd previously installed. No earth-shatting vacuum-related fisacos to date.

 

[fixizin]

There is spark energy leakage long before visible corona.

But how can the DIYer detect and measure it?

Should I start by grabbing the neg batt terminal with one hand, and with one lead of a 10k resistor in the other hand, run the other lead of the resistor along each plug wire in turn? If no "tingle", repeat with a 5k, then 1k, then 330 ohm resistor in turn? LOL!

If still no tingle, then clean up the wires with silicone spray and elbow grease, and get on to the next item?

 

[shadetree]

A hard hard hard vacuum the likes of which you'll find in deep space is still less than 15psi trying to hold that boot on. That boot is less than 1/4 of one square inch area against that terminal. So, you're telling us that the 3-4 pounds of extra force generated by this vacuum will make it significantly harder to pull the wires?

Wires do get stuck, but your theory does not explain it.

Me, I use lots of grease. I work on more than my own vehicle. I've had to remove wires I'd previously installed. No earth-shatting vacuum-related fisacos to date.

Theory or no theory, it happens. You just haven't been there yet. No matter you computations, when the damn boot is in a difficult place, and you are trying to pull it off with a couple fingers, yes, it makes it almost impossible to pull the thing off. Do you ever hear a "pop" when you remove the boot? Where does that noise come from???? Why use more grease than necessary? More is always better, right????? shady