Ground Cable on Coil Leads and Wire Resistance
 

Hey guys...made an interesting observation tonight as I was replacing my primary coil and spark plug wires.

Firstly, when replacing the primary coil lead with a new unit from Mazda, I noticed that the one already on my car had a ground cable coming out of it while the new one did not have this cable. Did Mazda change that part at some point? Was it discovered that the ground cable was unnecessary?

Secondly, I was replacing my old Jacobs wires with some new 10mm Magnecores and I tested the resistance in the wires to check. The Jacobs wires had resistance values of around 250-300 ohms while the Magnecores had resistance values at around 1200-1500 ohms (or something in those whereabouts). The manual said that the wires should have resistance values at around 16,000 ohms, but I'm assuming that's for the stock wires. Do these values sound about right? Are the Jacobs wires really that much more conductive?

Any input is appreciated...thanks!
Allen

oh yeah they are. . . stockers are that resistant because of rfi. racing beat wires are about the same. if you look at msd wires or taylor wires. . . they have around 25-60 ohms/foot for resistance. that doesnt help your ears in the cockpit, but it sure does help deliver the most spark possible. :D

paul

The current model coil harness does not have the ground wire. Apparently they decided it was unnecessary.

I make my customers wires from MSD wire that is 40 ohms per foot . Never a problem in about 6 years .

Thanks for all the feedback guys...very helpful. I did some brief research on resistance and efi and rfi, and bottom line is that it looks like everything is a compromise in one way or another. Low resistance is ideal, but with that usually comes higher efi and rfi...I'm guessing that there is a "plateau" of sorts on when lower resistance becomes less beneficial marginally, and I'm pretty comfortable with using the Magecors are they've been around for quite a while and seem to know what they're doing. The construction of their wires was phenomenal...all one piece.

I think there was an FAQ on that grounding strap on scuderiani or robinette. I remember reading it somewhere.

Hmmm...tried searching both sites but to no avail. Scuderia doesn't seem to have a search function anymore since the move. Do you remember anything about it? I'm assuming that if Mazda is using this part number for anybody that orders it, I'm assuming they've figured it was unnecessary for ALL FDs, but I could be wrong...anybody know if this will hurt my motor?

Well I received assurance from my mechanic that it was totally fine, but I'm still curious to the FAQ that you were talking about...if anybody knows of the reference, could you let us know?

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/new-ignition-stuff-70779/

I have a coil harness with the grounding removed if anyone needs....

Ahh...thanks for that link! So basically there were arcing issues with the ground strap. Good to know...