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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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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 · #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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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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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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