| Author |
Message |
James Selevan (Jselevan)
Junior Member
Username: Jselevan
Post Number: 142
Registered: 6-2002
| | Posted on Thursday, September 19, 2002 - 11:21 am: | |
Hans has got it right. First, Henry's initial thought about increasing resistance leads to increased voltage is accurate for the resistance, but not for the sparkplug. Increased resistance in the wire will lead to more voltage drop in the wire, leaving less voltage for the sparkplug. Remember, the sum of the voltages around the circuit (loop) must equal the source voltage. Thus, if 30,000 volts are generated, and 20,000 volts are seen across the wire, this leaves only 10,000 volts for the sparkplug. However, as Hans notes (see below), without current flow, all the voltage is seen across the sparkplug gap.
Hans accurately observes that there is no current flowing until discharge across the sparkplug gap. Once discharge takes place, the current is limited by the wire resistance. I cannot comment on the relative resistance of the ionized gas versus the sparkplug wire, but this is important in understanding the "resistance bridge" that is created at the moment of discharge. If the wire resistance is too great, then during discharge (current flow) more voltage will be dropped across the wire, leading to a shorter ionization period. On the other hand, the resistance in the wire will prolong the capacitor discharge period (time constant = Resistance x capacitance) if this is a capacitive discharge circuit. Finally, there is the possibility of "ringing" of the RLC circuit if not properly damped.
Without knowing the internal design of the high voltage output circuit, it is best to adhere to the manufacturers recommendation.
Finally, and most interesting, I did not notice any difference engine performance before and after changing the wires - and my wires did have virtually infinite resistance. In fact, and much to my chagrin, I did not notice any difference before and after the 30k service. |
Hans E. Hansen (4re_gt4)
Junior Member
Username: 4re_gt4
Post Number: 183
Registered: 4-2002
| | Posted on Thursday, September 19, 2002 - 12:09 am: | |
You need to practice a bit with Ohm's law. The spark plug gap offers infinite resistance, UNTIL the spark jumps. Then the resistance offered by the ionized gases is quite low. Resistor wires will limit current. If the ignition system is designed with resistor wires in mind, they will not stand up to the essentially zero resistannce offered by solid core wire when it fires. Too much current. EMF interference in the radio is related to this current. Less current = less interference.
Also, the ignition coil has a finite discharge time, dependent upon its load, similar to a capacitor. T=RL. If presented with a significant resistance, the spark will be longer in duration.
Hans. |
Henryk (Henryk)
Member
Username: Henryk
Post Number: 270
Registered: 8-2001
| | Posted on Wednesday, September 18, 2002 - 11:11 pm: | |
Jim: Correct me if I am wrong......with higher resistance comes more voltage, and that is what fires the plug.
Since the spark plug gap offers it's own resistance, then why would one want additional resistance in the wires...to increase voltage?....why not just increase the gap?...... unless it was for radio supression?
I would consider the 0.5-1.0 ohms as essentially zero in the extenders.......since every length of wire has SOME resistance.
Hence, it seems that I should replace my wires.
When you replaced yours, with infinite resitance, and the car running fine, did you notice any difference with the new wires? |
James Selevan (Jselevan)
Junior Member
Username: Jselevan
Post Number: 141
Registered: 6-2002
| | Posted on Wednesday, September 18, 2002 - 10:49 pm: | |
Henry - the extenders should be essentially zero. The wires are between 500 and 2000 ohms. I replaced mine during the 30k when I found several with infinite resistance (at least on my inexpensive multimeter). Despite these open circuits, the car was running fine. I suspect that the voltage was making its way down the conductor, and as there is little current flow, the high resistance did not negatively impact performance. The 500 ohms is to create a Resistor Capacitor circuit that suppresses electromagnetic noise (radio static). You can procure zero resistance wire. I believe that the electronic ignition anticipates a small load along the spark plug wire, thus I am uncertain as to the wisdom of using zero resistance wire.
Jim S. |
Henryk (Henryk)
Member
Username: Henryk
Post Number: 267
Registered: 8-2001
| | Posted on Wednesday, September 18, 2002 - 10:32 pm: | |
Can anyone give me the ohm readings on new plug wires for the TR; also the extenders.
I measured mine, but they vary too much. Possibly need new wires. The engine does not miss. I just had nothing better to do, so I measured the resistance in the wires, and extenders.
The wires vary greatly, while the extenders are betwee 0.5-1.0 ohms.
Thanks. |
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