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Discussion Starter #1
This is a strange one.

Last night I noticed a rough running condition on my 94 RRC. There would be a misfire every few seconds accompanied by a tick from under the hood. With the truck running I can see arcing and electrical energy flow from the +/- terminals on the coil to the coil tower(spark output to dist).

The coil is a new Bosch part and the ignition amplifier has been replaced recently with a genuine LR part. Both the coil and the amplifier have been relocated to the driver fender and are securely bolted down with very clean grounds.

Other than the rough running at idle the motor runs great.

I tried resetting the coil wire several times with no change. I can see electricity flow from the +/- terminals under the coil wire boot like water flowing. So strange.

Any ideas on what to look at or ways to insulate the coil boot better would be appreciated.
 

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Are you sure you have the correct style connector on the coil wire for the new coil? also check the coil wire at the distributor end. The electricity is going to take the path of least resistance, so if there is a higher resistance in the path going to the spark plug arcing will occur up stream to dissipate the energy through the easiest path.
 

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Discussion Starter #3
I am using genuine Land Rover plug wires. I do see a gap around the coil wire boot and the coil tower. I was going to try cinching down the boot with a zip-tie just to see if eliminating the gap fixes the issue. Was also considering putting rubber boots over the +/- coil terminals to further insulate the path. There is no arcing at the distributor end and both terminals are very clean. I will check to see if there is proper contact between the distributor cap and the rotor.
 

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Discussion Starter #5
Sounds like it needs to be pressed on better. On mine, i had to pull the wire from the boot, press everything into place, then slip the boot over afterwards. In a pinch, electrical tape does wonders.
Yep, tried that. Going to troubleshoot more tonight.
 

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The coil could have a crack in the ceramic at the top? The wire boot could be torn too....
 

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Discussion Starter #7
Quick update

Tried resetting terminal to coil tower to insure proper seating of the wire. No change.
Added dielectric grease to coil wire boot. Small improvement.
Cinched a zip tie around boot to further eliminate air gap between wire boot and coil tower. Small improvement.

After applying these countermeasures there is no longer strong arcs that cause the engine to misfire, but I do still see electricity flowing from the cam tower to the +/- terminals on the coil, albeit much less than before.

Removed distributor cap and inspected rotor and cap to find them both being in nearly new condition and genuine Land Rover parts. I don't believe the issue is with those parts.

But, while poking around the engine while running I saw blue arcing coming from the coil wire anywhere it came close to a component with a ground. I think the coil wire should be replaced as the first measure. Thoughts? Anybody know where I can get just a coil wire?
 

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If the coil wire is breaking down and arcing through the insulation, I would be suspect of the rest of the wire set as well. Why not replace the entire set so you know you have good wires throughout?
 

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Discussion Starter #10
If the coil wire is breaking down and arcing through the insulation, I would be suspect of the rest of the wire set as well. Why not replace the entire set so you know you have good wires throughout?
This is what I will do once the failure is confirmed. If a new coil wire fixes the problem I will replace all wires. Magnecor seems to be the wire of choice.
 

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Discussion Starter #11
Quick update.

Swapped the coil wire for a new part and it definitely fits better. The air gap between the coil wire boot and coil tower is no longer there. Electricity is still arcing from the +/- posts to the coil wire and is causing misfires and rough running. Going to order another coil to see if it makes a difference. It seems like there may be a bad ground somewhere. I plan to locate and clean all engine compartment grounds I can find.

The search continues.
 

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Discussion Starter #12
Quick update:

Have not swapped out coil yet.

Instead I've been trying other components to see if I can isolate the issue further. Plug wires and distributor cap have been replaced with no change to my situation. I am going to reinstall the cap and plug wires to minimize the variables as I continue to troubleshoot the system.

I pulled a spark plug to find it very clean but old looking and the gap was wider than spec at 0.040". So, new spark plugs will be the next step.
 

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I find all of this a bit peculiar. Normally things only arc if the wires are very far gone. Insulation gaps indicate you have some wrong components in there, everything should fit snug to the point that you cannot get the darn things off.

The coil generates high voltage which travels down the leads to eventually arc out to earth at the (correct plug). The gap at distributor arm and the plug is small and very easy for the electricity to jump over which will be by far the preferred path for the electricity to take. Arching elsewhere would indicate that either there is an earth closer by and/or the path to earth via the spark plug is severely hindered.

Distance is a relative thing for electricity. Most likely your normal path is hindered and grown 'long' dt

-broken coil (internal short etc)
-badly degraded wire(s) excessive resistance.
-completely out of sync distributor (large gap)
-broken distributor arm (fairly common I believe)
-wasted spark plugs
-poor engine earth,

Although it does not make a difference in engine running, when you change plugs you need to consider either resistor plus or resistor wires, not both or neither. This will impact electrostatic interference on electric systems such as radio etc.

There are not that many items in the system and most can be measured. Follow the path the electricity is meant to travel and buy parts which are know correct for the Range Rover application. Don't be scared to look beyond your local parts supplier. The UK is a good source for parts, much cheaper with fast and affordable shipping.
 

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That's the coil that is faulty, it just should not track HT current to anything.

Once it establishes a "track" for the voltage to travel you won't be able to correct it.

There was either a pre-existing fault in the coil insulation or it has been caused by mechanical fracture.

Resistance in the following HT system wouldn't help it but also would not cause it.
 

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Discussion Starter #15
Update: Problem Solved!!!

So, in an effort to be as thorough and scientific as possible I put all the original ignition parts back onto the truck and confirmed the arcing was still happening before installing new spark plugs. Each plug was inspected after it was removed. They were the correct Champion RN11YC parts and they looked to be in fairly good shape with clean electrodes and no visible cracking or degrading on the ceramic, but all the gaps were out of spec. From what I've found spark plug gap should be set between 0.032" and 0.038" what was found on the removed plugs were gaps ranging from 0.038" and 0.042".

Suspecting I had a resistance issue in the high voltage circuit I installed Champion RN12YC plugs pre-gapped to 0.032" to see if this changed anything. Keep in mind that I have all the original components installed and confirmed the arcing was happening right before changing the plugs. The new plugs have eradicated the rouge arcing!

The truck runs significantly better than it did before! Crazy to think that a little wider plug gapcould induce so much headache. Thanks for everyone's input.
 

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having similar issue but unlike the OP wasn't able to sort with new plugs (RN11yc) gapped at 35.

The backdrop is an RPI 4.6 engine in a 95 LWB with the original coil and dizzy and plugs with about 25k on them. I decided to upgrade to the rpi amp/new bosch coil/new dizzy supplied by rpi. the new setup started arcing at the coil from the getgo. swapped in the original coil...same arcing.

went back to original dizzy with new plugs and the new bosch coil (thought it might be the rpi amp) and still got the arcing. finally, swapped out the bosch coil for the original (eg back to where I started) and all was good. if fairness to the bosch coil, it may have been fine at one point but appears to have a carbon trace from the arcing and not sure that can be undone (maybe so)

I think the arcing is simply the high voltage finding an easier way to ground than through the plugs so it would stand to reason somewhere in the path with the new setup, resistance has increased somewhere. the new bosch coil has about 1k higher resistance than the original (8.5 vs 7.5) but not sure that would be the issue (maybe).

so stumped as to what it may be. I've tested each of the magnecor sport 80 wires and they range from a low of a little below 5k to almost 7k.

from the list earlier in the thread:

broken coil (internal short etc) - ok, as it works in the original config
-badly degraded wire(s) excessive resistance. - maybe something here given the varying resistance values
-completely out of sync distributor (large gap) - think this is ok
-broken distributor arm (fairly common I believe) - ok as well
-wasted spark plugs - replaced them so ok here as well
-poor engine earth, - think I have good earth at the coil

so stumped as to what it may be. hopefully others have sussed this issue and have suggested paths to follow, thanks
 

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It's certainly strange that so many coils are giving you the same observed fault.

Basic check, measure the depth of HT post internal on the coil, then compare it to how far you are locating the lead end into there during installation. They have to be right to the bottom to get the HT metal well away from the outermost tip of the insulation tower, which is why the tower extends that far. I pull the rubber cover away, insert the lead all the way in first and then place the cover using silicone grease to push as far down as possible. Make sure your HT king lead has the coil specific end placed there as they can differ end to end from the distributor mount on some manufacturers. I prefer the straight lead approach for the leads i use as opposed to the 90 degree type for coil end.

My experience has been that once a carbon track is clearly observable, then it's unusual to recover from that status. I never routinely replace these components unless I can prove failure so not prone to swapping out usually but will admit defeat if this condition is clear.

I run with resisted carbon silicone leads, plus resisted plugs (NGK BPR6ES) reliably with zero external tracking of HT power. Have done on these engines for more that 25 years, confident it's not resistance in the leads that's the origins of this problem.

Plug gaps, I run them on the absolute minimum of their specification and never open them wider.

The problem you describe is unusual because when the coil is fired to produce HT output it's the low tension "negative" coil terminal that's being switched down (so no earth present) to force the coil to spark. This is done by having the positive 12v supply to coil from ignition switch (this is how you turn the ignition on and off) with the ignition amplifier controlling the earth line via a a heavy duty transistor. The earth line switched down forces the accumulation of volts in the high tension side of coil to exit via nearest earth but this post has no earth during the HT fire event, making the exit route easiest through the leads.
It may appear to go to the earth terminal but I'd suspect it may "daisy chain" out to the coil's casing which is earthed.

Anyway, worth exploring your HT lead fitment to appreciate if there's anything to be gained there, then let us know what you've got.
 

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thanks for the detail RRLondon.

per follow-up discussion with RPI, they are suggesting the issue could be the plugs. They use the same magnecor 8mm wires I'm using and we've compared resistance values on those to make sure all good. However, they use NGK BP6ES (no R). I did see on the NGK website 1 ohm versus 5000 ohms between the original and the updated R version of this plug. I'm still not completely convinced that's the issue as I have no arching after going back to the current original setup (the champion plugs). there has to be something about the new setup (new dizzy, new coil, new amp) that is the culprit.

I did noticed the old coil seems to have a lot of fluid in it and the new doesn't.

To clarify on the new coil trace mark....it's arching (and trace formed) to the + terminal on the coil not the -. when arcing, the effect is no spark and an intermittent missing (going from intermittent to almost not running as the arc/trace more fully forms on the plastic tower and the arcing becomes the norm not the exception). I would think sanding off the carbon trace would remove this path but sounds like from your experience that doesn't fully remove it. Perhaps the trace is actually burned deep in the plastic tower at this point so no amount of sanding can address. sounds like it's toast.

Haven't focused on it, but wondering if the new dizzy could be contributing. was wondering if a resistance test from king lead at coil to spark plug #1 with dizzy rotor at #1 in cap might reveal issues between the dizzy's but think I'm starting to look for ghosts as the new dizzy is well...new and the old Lucas looks like its been through hell and back. supposed I should fit the new dizzy with the old components and see if all the same to rule out the new dizzy having a role in the issue.

Ragarding your suggestion on the coil tower and input. I compared the king lead insert on the current coil to the new Bosch. The current has what looks like an adjuster screw inside the lead insert whereas the Bosch does not. Perhaps that design has a better connection/path. As such, the insert on the Bosch is deeper. However, I tested the insertion length on the king lead wire and it fully seats. Don't think this is the issue as I got the arching using the old coil with the new dizzy and new RPI amp.

I'm wondering if the super spark coming from the RPI amp requires as little resistance at the plug as possible. Just seems like that's the only real change from my legacy setup (suppose that's why RPI sells it as a package and not piecemeal)

I will report back once I've fitted the new plugs.

If anyone else has the RPI amp fitted, please weigh in on your component path.

Thanks
 

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Certainly a bit of a puzzler ;)

Immediate question springs to mind though, you've not got the coil wired in it's opposite orientation by any chance? To check, you should have 12v positive feed to the + terminal with ignition on and not running.

The amplifier switches the - negative line to make the coil function. This often confuses initial overview of the system (in other words, how can switching a negative do anything) to any positive effect.

I think it will work when wired backwards, but it's not designed to do so. Worthwhile checking with voltmeter to establish what you have.
 

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Regarding the coil +/- poles....

I did check that I had DC voltage on the after ignition lead wire (12.77vDC before start) and that it was going to the + post of the coil. The bosch coil has a plastic top cap with the +/- stamped so I took that off to ensure it had not been flipped (as there is +/- stamped on the top coil pressed casing as well). all good there. there is a spark arrestor (I think that's what its called) installed to the - post on the original coil tied to the same spot where the engine ribbon ground is tied to the body next to the coil. RPI said I did not need that so it was removed with the new installed (re-installed currently with the original coil).

to be specific on wiring:

original install: + post has the 12v feed post ignition AND the + dizzy lead; the - post has the spark arrestor, - dizzy lead, and injector wire communicator wire bundle lead

new install: 12v lead same, injector wire, same, spark arrestor removed completely, +/- coil leads to RPI amp instead of direct to dizzy and then +/- from RPI amp to dizzy
 
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