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Discussion Starter · #1 ·
I solved my crossfire problems with new plug wires, but after doing some research on the subject, I find it hard to understand the term "inductive crossfire".

Crossfire is when the wrong cylinder gets the spark, vs a misfire when the spark (if any) doesn't fire the cylinder.

Crossfire can come from leaky wires where the spark jumps from one wire to another. If the victim wire is next in the firing order, bad things can happen as the victim piston may be at 90 deg BtDC. If it happens to another cylinder, it may fire when the fuel is already burning, or the piston so far down, the mixture won't ignite.

In my case, I suspect it happened in the dist cap. Bad wires plus the higher energy needed to jump the sparkplug gap of the cylinder under pressure may have made the next terminal inside the cap the path of least resistance. I certainly didn't see any sparks around the wires during my midnight test.

Then there's "inductive crossfire" where the electric and magnetic fields of the source wire is supposed to induce a spark in a victim wire. I can't see this happening. Not only are two parallel wires a very inefficient sort of transformer, but in order for a victim wire to produce a spark, there must be a complete circuit. So where does the dist cap end of the victim wire get its ground from? This supposed spark has to travel from the victim wire, through the spark plug and back to the other end of the victim wire.

I can't see this happening, yet it appears to be an undisputed fact in all the research I can find on the subject. Anyone know more about this? Thank-you.
 

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I was first made aware of this crossfire phenomena back around 1980. It was in a service bulletin about the HEI Ford 5.0L. Firing order 15426378. If the plug wires for cylinders 7 & 8 were ran side by side, it would detonate the pistons out of both of the cylinders.

Over the years working on cars, I have found literally hundreds of cars with slight drivability issues. On all of these, someone had bundled the plug wires together, and zip tied them tight.

Just the other day, I had one running pretty ragged. I could here little ticking sounds from the plug wires, but I could not see any spark arching to ground. I even took one wire off of the spark plug, and hooked up my spark tester, and layed it across the plastic engine cover. I then ran my grounded test light along the whole plug wire, and could not find where the 'leak' was. I figured it was the wrong spark plugs for the application, that had taken out the plug wires. I also routed the new plug wires away from each other, and it ran fine.
 

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Discussion Starter · #3 ·
Those ticking sounds are sparks. Inductive issues would be silent. I agree about the routing and having that same firing ordeer you mention, I do keep 7 and 8 apart, but for arcing over, not induced spark from magnetic fields.

Thank-you for your reponse though. I just have an inquiring mind on this one and any info helps.
 

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"but in order for a victim wire to produce a spark, there must be a complete circuit."

I have wondered about this also, but have experienced the same things on several motors that were related here by carsavvycook.

I used to have a little tool that looked sort of like an X-Acto knife. It had a bevel on the end that was half round and you laid it against a plug wire to check to see if there was current going through the wire. There was nothing else hooked to the tool, but if you laid it on a live wire, the light in the tool would illuminate. How could that work???? :eek: That must explain induction from one wire to another, I don't know for sure.
 

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Induction is well understood in industry. Any time you run wire in a cable tray for any length you must and should separate power wiring (120AC+) from instrumentation wiring (24vdc). Over long cable tray runs it is not uncommon to have +90 volts induced into 4-20ma instrumentation wiring.

Vince
 

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302 Z28 said:
Induction is well understood in industry. Any time you run wire in a cable tray for any length you must and should separate power wiring (120AC+) from instrumentation wiring (24vdc). Over long cable tray runs it is not uncommon to have +90 volts induced into 4-20ma instrumentation wiring.

Vince
Thanks Vince :thumbup:

Now take into consideration, that you have anywhere between 35,000 to 45,000 KV's pulsing through a resisted plug wire, trying to find it's way to ground, which is normally through a resistor spark plug.

As that spark plug wears, and the gap get's wider, or the resistor in it starts to increase it's resistance. That amount of KV's is going to go down the path of least resistance.

They will 'crossfire' when ran next to each other, without any visible signs of damage. It is when two cylinders that are adjacent to each other in the firing order, that it gets really noticeable.

I honestly believe that this is why vehicles that do not get tuned on a regular basis, are the ones that require major engine work sooner than normal.
 

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Discussion Starter · #7 ·
Techinspector1: I have one of those tools. It works the same way as a radio transmission causes a flourescent tube to glow. Point the tube at the source and the electric field is stronger at the end of the tube closest to the RF source. The other end is in a weaker electric field. The difference between the two causes the bulb to glow. Turn the tube sideways to the source and the electric field is more or less the same at each end of the tube and it doesn't glow.

(Magnetic Field) Induction between two parallel wires will cause a voltage to build up between the wire ends, but we still need a complete circuit for current flow.

Vince, yes, that kind of power line coupling to small signal wires is well understood. Hence the requirement for shielded wire and twisted pairs. However in these cases, the victim wiring is in a closed circuit and current can flow.

I suspect that if induction coupling of ignition wires does exist, it must soomehow be related to Techinspectors example. I just havn't grasped the complete circuit in order for current to flow.

Why do I care? Just went through Hurricane Bill and am stuck indoors until the weather clears. So my mind wandered to a recent crossfire problem I had and thought it would be nice to understand it better.

I appreciate all your inputs. Thank-you.
 
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