cantdrv65

iTrader: (3)

The best way I have found to test for a faulty plug wire is put the car in high gear and lug the engine. Or just reach around in the engine bay until you get the **** knocked out of yourself(more of an accidental approach).

joecar

I can relate to that, it's supposed to be like therapy, isn't it...?

gametech

iTrader: (1)

I've found that the "open your engine bay at night and watch for fireworks" technique isn't nearly as painful.

Okie5.3

iTrader: (1)

a meter is sufficient to simply check the resistance of a conductor. i.e. plug wire. to test the insulating properties of the protective covering a megohmmeter or megger should be used.

not trying to disagree with anyone...

but unless there is some sort of insulator (dielectric) between the conductors (twisted wires), there cannot be any capacitance, which is demonstrated by measuring the resistance of the spark plug wire using a dc powered meter. capacitance reactance (Xc) resists DC current flow, therefore would indicate an open when measured with a dc powered meter.

also since the conductors generally are not twisted around an iron core of some sort, and the voltage produced by the coils resembles AC current, would rule out inductance. an inductor resists, or chokes out AC current, but allows DC current to flow. the amount of resistance an inductor has to AC current is directly proportional to the frequency of the signal.

this would then lean towards more of a purely resistive circuit.

oh, and my MSD wires were all ~43-44ohms.

brady346

iTrader: (13)

A friend and I tested a set of msd wires and checked them at about 45 ohms. Just for the heck of it, he tested a wire off of his restored H Farmall tractor, restored in the 70's, and those wires tested 9 ohms.

Adrenaline_Z

Are you trying to imply that there isn't any sort of inductive, or capacitive
properties within the ignition wires of an automobile because it's a DC charge?

Okie5.3

iTrader: (1)

using MSD wires for example. there is no measureable amount of capacitance in these wires. reason is the two bare copper conductors are tightly twisted together without the use of any dielectric material. twist together the same copper conductors with insulation material on each one and you may have capacitance depending on how much (length) is twisted together.

to verify any capacitance of an MSD wire, take a meter set it to read resistance and measure across the wire. if there is any capacitance the meter would go from no or low resistance and slowly climb to infinity. if it does you have capacitance, if not you don't.

as far as inductive properties of spark plugs wires, depends. using the MSD wires as an example again. the same two bare copper conductors are not twisted around a piece of ferrite, so any amount of XL would also be insignificant. this could also be verified with a meter using the resistance setting. an inductor would read infinity initially and drop to read low or no resistance.

more than likey in the case of the spark plug wires there is a X=0 state, meaning XC and XL are equal therefore leaving a purely resistive circuit.

Keith

Have you guys heard of how Harley Davidson measures detonation in their twin cam engines?

From what I have heard, they use a secondary voltage across the spark plug and measure the resistance. That will tell them the cylinder pressure and therefore if knock is present. So then would aftermarket wires on these engines affect the detonation measuring capabilities?

Adrenaline_Z

The insulator to create the capacitor is found in the spark plug. The gap of
the plug is a break in the DC circuit; the air and fuel pressurized within the
cylinder in the insulator. You now have a potential difference between the
electrodes, and any residual charge remaining that cannot jump the gap,
stays in the wire creating stored energy as a capacitor would.


That's not how you measure reactance in a set of wires. The meter does
not produce a rising and falling field like the charging and discharging energy
of the coil. The meter also does not produce a frequency of pulsing DC. As
the RPM of the motor increases, so will the frequency of the pulsations.

If DC current cannot flow in a broken circuit (IE: spark plug gap), how does
the energy get into the wire? Think of how a transformer operates, it's an
inductive process. Since the secondary field winding is connected to the
spark plug wire, the voltage is also induced into the wire at the time the
secondary winding is charged (coil pack); or once the rotor reaches the spark
plug post (distributor).

Not at all accurate due to the above conditions.

joecar

Interetsing comments.

A megger would output upto about 1kV-2kV, whereas the ignition coils output somewhere from 30kV-50kV; can a megger reach this voltage...?

I don't follow regarding the twisted wires...?
The plug wire contains a single conduction path, either a carbon impregnated filament, or a conductor spirally wound around a ferrite impregnated core, so I missed what you said.

The capacitance mentioned previously is due the gap at the spark plug (with air:fuel mixture as the dielectric).

Edit: An it can't be a purely resistive circuit because the coil (which is a massive inductor) is in series.

Edit: Adrenaline beat me on the response...

Okie5.3

iTrader: (1)

ok, i think understand how you guys are looking at this.

you are equating the gap in the spark plug, with the air/fuel being the insulating (dielectric) material opposing current flow, to basically what an air core capacitor would be. the spark is derived from the sudden voltage increase from the coil charging, creating a difference of potential at the electrode and ground strap, which becomes so great it charges (ionizes) the free electrons in the immediate vicinity making them conductive, creating a path to ground for current flow discharging the built up energy from the coil and making a spark. whereas the difference in a capacitor, there is current flow until the capacitor is charged, and the energy from that difference of potential is not released across the plates when discharging, but rather reverses path and flows in the opposite direction.

i was looking at it from a different perspective, but i gotcha now.

joecar

Okay, I got my 30K mile Taylors on my bench and this is what I measure:
6 x 180Ω (average)
1 x 250Ω
1 x 540Ω

I was very careful in removing all 8 wires, so those last 2... go figure...?

The part store is shut today, so I'll just reinstall them till I get new wires.

bitchncamaro

I have a slight mis fire and been trying to track it down... What I've found out is MY brand new GMPP red wires Ohm at 370, MY brand new gm black wires LIST $160( out of the bx.) reads 720 Ohm , and my stock ac black wires w/60,000 miles read 350 Ohm...

waveoff

iTrader: (11)

Just got my MSD wires in. Resistance numbers are in the first post.

ZoFastSS

iTrader: (5)

Go Msd, and if you have headers, you can jimmy rig them enough to work with the Msd Wire.

joecar

What exactly are you saying needs to be done...?

Pics...?

waveoff

iTrader: (11)

Yeah, if you could post some pics of how to jimmy rig them that'd be awesome. I'm gonna get some pacesetters in the near future.

joecar

You mean the boots on the MSD Superconductor wires are too long and touch the header...?

Zymosis

iTrader: (7)

Stock wires: 365 ohms
MSD: 27 ohms for 7 wires, one was 240k ohms (Piece of **** MSD wires )

joecar

240Kohms, ouch, that's practically open circuit...

Aren't they guaranteed...? Will they replace your one wire with a good one...?