Spark Plug Wires Arcing

[adallak]

I am sure the wires are original AC Delco. Checked under the hood in a dark place for arcing. There was no arcing whatsoever with dry wires. Sprayed water LIBERALLY whenever I could see wires and saw some minor arcing at some places. The idle quality never changed, at least not enough I could see a difference.

Two questions.

1. Would not new wires arc if sprayed with water liberally?

2. Partially based on the answer for the first question, does it make sense to replace the wires while there is no arcing in normal dry condition?

Thank you.

[CoupeDTS]

From what Ive read its pretty common on LT1s. People will say they arc way down behind where you cant even see since they are pretty hidden to begin with. I bought super thick ones in a kit for LT1s I plan to install soon. They wont fit in the stock holders but Im trying to eliminate the possibility of arcing since it seems to be a problem on these engines.

[Cadillac Jim]

The PCM is pretty good at counting engine misses. Have a good mechanic look at your PCM's memory. A good engine will have absolutely *no* misses for weeks. At least that's what my mechanic once told me about my 1997 VIN 9 Northstar. I think it's true of any sequential port DFI engine with premium ignition, which would include the LS engines.

[adallak]

The PCM is pretty good at counting engine misses. Have a good mechanic look at your PCM's memory. A good engine will have absolutely *no* misses for weeks. At least that's what my mechanic once told me about my 1997 VIN 9 Northstar. I think it's true of any sequential port DFI engine with premium ignition, which would include the LS engines.

Jim, are you saying the PCM stores codes for misfires but does not show current or history codes when you run onboard diagnostics?

BTW, onboard diagnostics for Fleetwoods is quite different.

My cars are mechanic-free.

[adallak]

I think spraying the wires with water to provoke arcing is not after all such a good idea. After my recent experiments, I have noticed increased shutter under load which I attributed to weak ignition system. When you MAKE the wires arc by wetting them up, you actually compromise their insulation at the weak spots where arcing occurs. So, old wires which would never arc when dry can start arcing after they were sprayed with water. Just a thought, arguments are welcome.

[Göran W]

You may be correct that the problem increases BUT only if the wires are faulty or dirty! If so you are supposed to change or clean them, no????

[adallak]

You may be correct that the problem increases BUT only if the wires are faulty or dirty! If so you are supposed to change or clean them, no????

My point was that even old wires could serve longer if you did not make them arc intentionally.

[JimD]

Just to swerve back to your first post for a minute.

I am sure the wires are original AC Delco. Checked under the hood in a dark place for arcing. There was no arcing whatsoever with dry wires. Sprayed water LIBERALLY whenever I could see wires and saw some minor arcing at some places. The idle quality never changed, at least not enough I could see a difference.

In my 50+ years of electronic experience (including 30+ years hands on experience with high voltage vacuum tube RF transmitters), there is nothing that could be called "minor arcing". Arcing is either present or absent; there is no half way point.

Two questions.

1. Would not new wires arc if sprayed with water liberally?

They "should not".

2. Partially based on the answer for the first question, does it make sense to replace the wires while there is no arcing in normal dry condition?

Yes, if only from a preventive maintanence point of view.

The problem with looking for arcing at idle RPM in Park is, the engine is not under load and the voltage required to fire the plugs is a low as it will ever be.

Put that same ignition secondary wire set under the load of WOT at 5,000 RPM and you are dealing with some serious voltage required to fire the plugs.

If there is even a hint of arcing at idle, the secondary wires are garbage.

[adallak]

Just to swerve back to your first post for a minute.

I am sure the wires are original AC Delco. Checked under the hood in a dark place for arcing. There was no arcing whatsoever with dry wires. Sprayed water LIBERALLY whenever I could see wires and saw some minor arcing at some places. The idle quality never changed, at least not enough I could see a difference.

In my 50+ years of electronic experience (including 30+ years hands on experience with high voltage vacuum tube RF transmitters), there is nothing that could be called "minor arcing". Arcing is either present or absent; there is no half way point.

Two questions.

1. Would not new wires arc if sprayed with water liberally?

They "should not".

2. Partially based on the answer for the first question, does it make sense to replace the wires while there is no arcing in normal dry condition?

Yes, if only from a preventive maintanence point of view.

The problem with looking for arcing at idle RPM in Park is, the engine is not under load and the voltage required to fire the plugs is a low as it will ever be.

Put that same ignition secondary wire set under the load of WOT at 5,000 RPM and you are dealing with some serious voltage required to fire the plugs.

If there is even a hint of arcing at idle, the secondary wires are garbage.

Thanks Jim.

1. Should not does really mean would not, right? I was curious if someone actually tried to spray water over NEW wires and see if they arc.

2. Sometimes people talk about "firework" under the hood. I did not see any firework and did not even notice sparks right away, so I do not know how else I could describe that arcing if not as a "minor" one. I do understand your statement though.

3. Could you please explain what you mean by saying a spark plug needs higher voltage under load? The conditions inside the cylinder do not change, right? Why a spark plug would need higher voltage? I think the coil should produce more POWER to support more frequent spars, but the energy and consequently the voltage of a single spark is the same regardless the load of the engine or RPM. Correct me if I am wrong.

[JimD]

....Could you please explain what you mean by saying a spark plug needs higher voltage under load? The conditions inside the cylinder do not change, right?

But the conditions inside the combustion chamber DO change between a no load at idle situation and a maximum load 5,000+ RPM WOT situation.

At the risk of over-simplifying the physics, a higher (much higher) voltage is required to fire the plugs at WOT. And yes, the coil is more than capable of developing the voltage required to fire the plugs at 5,000+ RPM WOT.

The voltage required to fire the plug gap at idle is (relatively) low; when the coil develops the voltage required, the plug will fire and the magnetic energy of the coil will be reset to zero in preparation for the next cylinder in the firing order.

Bottom line is, if you see even a hint of plug wire arcing at idle load (lower voltage requirement), you will suffer a mis-fire under higher engine loads (higher voltage requirement). Simply because the electrical energy being developed by the coil takes the path of least resistance to chassis ground; which in the case of "leaky" plug wires, is the path through the wire insulation.

Carbon impregnated plug wires gradually lose their insulating qualities after some number of cold to hot to cold thermal cycles.

Without typing several 600 page text books, that's my 'simple' explanation. And I regret my classroom analogy/verbal skills have suffered from not being used.

[adallak]

....Could you please explain what you mean by saying a spark plug needs higher voltage under load? The conditions inside the cylinder do not change, right?

But the conditions inside the combustion chamber DO change between a no load at idle situation and a maximum load 5,000+ RPM WOT situation.

At the risk of over-simplifying the physics, a higher (much higher) voltage is required to fire the plugs at WOT. And yes, the coil is more than capable of developing the voltage required to fire the plugs at 5,000+ RPM WOT.

The voltage required to fire the plug gap at idle is (relatively) low; when the coil develops the voltage required, the plug will fire and the magnetic energy of the coil will be reset to zero in preparation for the next cylinder in the firing order.

Bottom line is, if you see even a hint of plug wire arcing at idle load (lower voltage requirement), you will suffer a mis-fire under higher engine loads (higher voltage requirement). Simply because the electrical energy being developed by the coil takes the path of least resistance to chassis ground; which in the case of "leaky" plug wires, is the path through the wire insulation.

Carbon impregnated plug wires gradually lose their insulating qualities after some number of cold to hot to cold thermal cycles.

Without typing several 600 page text books, that's my 'simple' explanation. And I regret my classroom analogy/verbal skills have suffered from not being used.

Thanks. So, at WOT electrical properties of air/gasoline mixture change compared to idle? Richer mixture requires higher voltage for spark? Interesting, but not that obvious.

[JimD]

Thanks. So, at WOT electrical properties of air/gasoline mixture change compared to idle? Richer mixture requires higher voltage for spark? Interesting, but not that obvious.

Whoa. The air/fuel mixture is maintained at the stoichiometric target of approximately 14.7 to 1 regardless of emgine RPM or load. Search on stoichiometry.

What changes is the pressure in the combustion chamber.

If the dynamics were obvious, we would not be consuming all this bandwidth.

[Cadillac Jim]

The PCM is pretty good at counting engine misses. Have a good mechanic look at your PCM's memory. A good engine will have absolutely *no* misses for weeks. At least that's what my mechanic once told me about my 1997 VIN 9 Northstar. I think it's true of any sequential port DFI engine with premium ignition, which would include the LS engines.

Jim, are you saying the PCM stores codes for misfires but does not show current or history codes when you run onboard diagnostics?

BTW, onboard diagnostics for Fleetwoods is quite different.

My cars are mechanic-free.

The only code my car throws for misses is P0300. The 1997 FSM pages on that DTC, 6-426 through 6-429, gives a long list of conditions under which this DTC will not be thrown, including idle, throttle movement, heavy throttle, redline RPM, other tests and PCM commands are not present, etc. I've never had that code.

Once I noticed a one-fire glitch at idle after stopping and asked my mechanic to check it out. He looked into the data in the PCM and said that the miss count was zero, and that the glitch was probably the PCM adjusting conditions, and he was right. We found out later (a P0420 code and follow-up with his OBD II reader, showing the waveform at the output of the cat mimicked the waveform at the input too well) that the cat was cracked, and when a piece of it shifted, the PCM adjusted within milliseconds. A new cat fixed the problem. Examination of the cat, once out of the car, showed the crack. It was a new one that had been dropped in the box in shipping and handling.

[CoupeDTS]

Good info

[adallak]

Okay. I see. Depending on throttle angle, dielectric conditions in cylinders change so that more voltage is required for a healthy spark. That makes the wires more vulnerable for arcing and engine more vulnerable for missing at higher RPM.

By the way, the FSM does not say the wires should not arc at all. It only says that the wires should be changed if they are visually damaged or if the quality of IDLE changes or engine STALLS when the wires are covered with thin layer of water. According to the FSM, minor arcing I saw at idle was fine since idle never changed leave alone engine stalling. I am not saying I would mind if wires did not arc at all, but, perhaps, those who put together the FSM considered acceptable extent of arcing.

I have ordered a set of AC Delco spark plug wires from online source I never used before. Surprisingly, they not only offered the lowest price I could find, but also next day air UPS FREE shipping for orders more than $50. You might want to check it out: http://www.autopartstomorrow.com/