Worn spark plug wire was causing my engine problem

Last year the problem first revealed itself when I was riding in Florida, on my way to Key West: I started experiencing engine hesitation (misfiring), especially when accelerating. Wet conditions seemed to make the problem worse.  In hindsight, I realize that wind also aggravated the problem.

As I wrote in an earlier blog post, Jimmy at J&D Cycles in Morrisville, NC discovered a broken air filter bracket when I got back from Key West. I thought that was the source of the problem. (Wrong.)

As you also may have read in a previous blog post, I tried throttle body cleaner, thinking that restricted air intake was the source of the problem. Nope. I then changed the spark plugs. Nope again.

Two weeks ago, I took the bike into the local dealership for a Dyno Tune. On my previous bike, a 2000 HD Road King Classic (FLHRCI), I had a problem with similar symptoms. In that case, I had had the dealer install the Screamin' Eagle® Big Bore Stage II Kit. When they did that, they failed to remove my Power Commander, which was no longer needed because the dealer's upgrade included a new Electronic Control Module (ECM). The Power Commander was interfering with the settings of the new ECM, throwing my ignition timing off. An old fella at the HD dealership in Johnston City, Tennessee happened to be chatting with me one afternoon when I was riding out that way. I mentioned my problem to him and after sharing some details, he barked at me, "take that damned thing off" - referring to the Power Commander. "You don't need it with the new ECM!" He was absolutely right. I removed the Power Commander and the timing problem went away with it.

I have a Power Commander on this bike, but with the stock ECM. So, I thought may a tuneup would fix the problem. That is, I thought that if the dealer adjusted the map on my Power Commander to match my current set up, the timing problem I thought I was having would be resolved. Nope again.

The Dyno Tune improved the engine performance somewhat, but the hesitation problem remained. How they missed the actual source of the problem during the three-hour Dyno Tune mystifies me. (I will write in another blog post how a $300 tune ended up costing me $860.) 

So, a couple of weeks ago, I went back to Jimmy, desperate to find the source. I'm riding next Tuesday to Machias, Maine and the Adirondacks for a 10-day tour and I need my bike in optimum condition.

We ran down a checklist of potential sources for problem and decided to go for new spark plug wires next. They cost me $20.95 for the pair. I picked up the bike today. After more than a year of trying this and trying that, we finally discovered that the engine hesitation problem was resulting from a leaking spark plug wire!

(Click on the photo of the spark plug wires, above right, to view a closeup of the hole in the upper wire.)

It turns out that one of the wires was rubbing against a metal edge on the engine and after 70-80,000 miles, the vibrating surfaces had worn a hole right through the insulation.

Just for geeky fun, I got my ohmmeter out and checked the resistance on both wires. One was about 6.8 Kohms (see photo) and the other about 6.4 Kohms. The official Harley Davidson maintenance manual (Part No. 99483-06) specifies a resistance of 5 - 11.667 Kohms. So, these wires were still in spec--when the one wasn't leaking a charge to the engine surface. Only a visual inspection of the wires would reveal the source of the problem.

I am now ready to ride to Maine next week. Amen!

Keep the shiny side up!

-The Long Rider