Spark plug wire expected resistance EFII

[tass]

Continuing my journey in installing System32 electronic ignition in my RV-4, I've begun sizing and crimping the spark plug wires.

However, the resistance I'm seeing looks very high - 25kΩ for a wire a few feet long. I know this is within spec for automotive cables, but I want to double check before crimping the rest in case I'm doing something stupid (these are the fold-back type which are slightly fiddly). I've seen some specs saying 50Ω per foot which is way off what I'm seeing.

Does what I'm seeing look about right? Does touching a multimeter probe against a non-crimped conductor give the reading of the wire itself, proving the crimp is good/bad? Or does the probe on its own not make good enough contact to give a reading with this type of wire?

 

[clam]

sparks plug wire resistance

A few years ago, I began having RFI issues in the VHF frequency range. I chased it down to the "left" EFII ignition. During my troubleshooting, I received the following from the EFII supplier, whom I have found to be very helpful in tech support of his products...

".. the resistance of your spark plug wires...should be approx 300ohms per ft"

I have always placed the multimeter leads on the crimped terminal, and this is how I've seen it done otherwise too, but I do not know how much this affects the reading.

As you continue the installation and testing, I'll add this too in case you run into RFI issues. It cured my problem immediately:

"You could have a broken conductor that is creating an undesired spark gap in a wire. If you want to take the shotgun approach on reducing radio frequency emissions from the spark plug wires, you could go to carbon core wires.
Taylor # 60651 from Summit Racing will knock down emissions dramatically."

 

[Dustyone]

MSD Ignition Leads

There is a very good reason that SDS specs the MSD Ignition Leads.

Watch this YouTube to learn more.

https://youtu.be/8kQDSlpKrCw?si=-ipVh2PB_14_b4vH

Apart from the incredibly strong leads, their stainless plug connectors clip on with a solid SNAP. These leads will not fall off and have the lowest resistance per foot of any leads available.

I have replaced one set of the blue leads that are supplied with the EFII brand ignitions because the leads would pop off during flight. Their lead ends are a soft tin? and not a hard stainless like the MSD.

 

[tass]

Thanks for the replies!

Funny, that MSD video is what I watched again right before crimping the first wires.

There might be nothing to it, but using the single crimp terminals just feels like you're putting extra stress on the conductor by bending it back over itself as compared to the other style. I might get myself a set of MSD. The taylor connectors it came with didn't have a very solid feeling - you're right about that, and definitely want to avoid them popping out.

Is there a particular set you remember getting?

Also, while I have you all, I was hard pressed finding pictures of how people run the cable from the crank trigger. Do you slot it in between the rubber baffles, then through adel clamps above the engine? I can't really drill a hole since the plug is so big, and draping it between the baffles had me picturing the canopy crushing it.

 

[Freemasm]

Can you verify something?

……

No air gap between the leads? While it’s probably good for many years, there is a risk (or so assumed forever). What does the supply and OEM state about such? Thx.

 

[MiserBird]

Plug wire crossfire

I had exactly the same thought since I have had cross fire breakdown happen to me with 7MM OEM silicone wires on my car. Limped off the interstate, separated the wires (lucky guess) and made it fine the rest of the way home. Easy to see the breakdown between the wires the next day. Replaced with 8MM.

 

[Ironflight]

I had exactly the same thought since I have had cross fire breakdown happen to me with 7MM OEM silicone wires on my car. Limped off the interstate, separated the wires (lucky guess) and made it fine the rest of the way home. Easy to see the breakdown between the wires the next day. Replaced with 8MM.

I’ll add that as pretty as that looks - it’s a beautiful wire looming job - at least one EI manufacturer says that wires must be separated, not bundled up against each other. I found ignition wire “combs” cheap on Amazon, and use them on all four of our EI-equipped engines. Does it make a difference? I don’t know, I just did it the recommended way…..

 

[riseric]

What Paul said. I seperated the leads.

I used the supplied blue Taylor leads and connectors.
I wrapped them in braided sheild for proctection.

Resistance was measured and found within specs.
I seperated them with combs bought in the aviation aisle of Canadian Tire.
100 hours of operation and absolutely no issues.


Did not test any other configuration.

 

[rv6ejguy]

I’ll add that as pretty as that looks - it’s a beautiful wire looming job - at least one EI manufacturer says that wires must be separated, not bundled up against each other. I found ignition wire “combs” cheap on Amazon, and use them on all four of our EI-equipped engines. Does it make a difference? I don’t know, I just did it the recommended way…..

With a couple thousand out there working fine in the field, most not using separators with the MSD stuff, it doesn't appear to be important. I have some carbon string Packard (GM supplier) wires on my Subaru. 20 years now and they are wrapped together for about 18 inches. No issues with misfires or radio noise.

I couldn't comment on other brands.

If wires went bad and were bundled, that could be a problem but could also be if they are too close to ground.

 

[vlittle]

One advantage of inductive-discharge electronic ignitions is that the spark voltage is typically lower (and longer duration) than capacitive-discharge ignitions (multiple short duration, high voltage sparks).

It's the higher voltages that can lead to arcing between old or degraded plug wires, hence the 'rule of thumb' for separating them.

Both systems can work well when new, but as things age, the inductive-discharge systems should be more reliable. That's what modern automotive engines use.

V

 

[Freemasm]

... since I have had cross fire breakdown happen to me with 7MM OEM silicone wires on my car....

.... Does it make a difference? I don’t know, I just did it the recommended way…..

...I seperated the leads....

....With a couple thousand out there working fine... No issues with misfires or radio noise...

The Low Probability, High Severity corner of the FMEA is always the hardest items to judge. The Taylor 8mm leads appear to be high very quality. The materials of construction and relative thickness would probably ensure the leads outlast the life of the aircraft. That said, the cost of the tie wraps to make combs was cheap, so I did.

Not a car guy but the ones I know have a common opinion regarding ignition leads; consensus being that the established aftermarket ones beat the heck out of the ones that come with the car from a quality/component life perspective. Nothing I've seen leads me to question that

 

[wcalvert]

Build it per manufacturer's directions and move on ... many have passed before you and they're not complaining about issues. Separate, parallel, 7 or 8 mm, Joe's brand or Jacks ...

Sorry for the blunt observation. You're closing in on the goals and have a plane to fly, fly it!