coil or cap failure?

[mtndragon]

OK, here is my scenario. I have an 04 ABS with 53K miles on it. Cylinder four is intermittently firing. I have read this:

https://www.fjrforum.com/forum//index.php?s...hl=coil+failure

and also read about others that have had caps that do not stay seated on plugs. I have changed all plugs and checked to make sure wires are seated. I spent a week trying to work out this issue with throttle body synching, unsuccessfully. I am currently traveling through California on my FJR, and I stopped in at Powerhouse Motors, in Paso Robles, where they were able to provide me with what I believe to be good diagnostics. The mechanic who spent three hours diagnosing my bike seemed to have significant experience with FJRs. He corrected my improperly installed recall TPS, confirmed that I do in fact know how to synch throttle bodies, checked compression, vacuum lines, and intake leaks. I did the valves myself two weeks ago, and it was reassuring to have him check off all things I could have botched in the process. He firmly believes that my problem lies in a faulty cap or coil. All other plugs were good, but plug 4 has a fair amount of carbon on it from not firing. The bike runs better than ever when all four cylinders fire which leads me to believe that the mechanic’s diagnosis is correct. The problem is below 5k cylinder 4 doesn’t fire very frequently. It mostly just misses and pops like an out of step drummer. Above 6k, and wide open, the bike pulls like, well…and FJR, smooth and clean with that rapidly winding purr. Below 5k, not so much. It has a rough idle, is inconsistent at lower rpms, and requires heavy clutch slipping until about 3k, where it runs like a limp dog until about 5 or 6k His suggestion was to pull the cap off 4 and put it on 1 or 2 to isolate the cap. If not, he believes it is a coil failure. As neither of these parts is readily available, and I am hoping to fix this myself, I carried on my way and I am currently in Lake Tahoe. The climb over Monitor Pass (8700 ft) did not change the behavior at all. Above 6K good, below 6K bad.

My questions are:

From anyone that has had a coil failure, are these the signs and symptoms?

Is it possible since the coil is firing two cylinders, that only one cylinder is not firing with a bad coil?

Thoughts?

Thank you.

 

[charismaticmegafauna]

Is it possible since the coil is firing two cylinders, that only one cylinder is not firing with a bad coil?

"Possible?" -- maybe; but probably not too likely IMO. Altho, one learns to never 'rule-out' anything.

First: one of the 'beauties' of a 4-cyl motorcycle engine w/'wasted-spark' ignition is that you have a very handy diagnostic tool in the other three cylinders. If, for instance, you run cyls 2&3 on the 1&4 coil and your problem goes to, say, cyl 3 -- Voila! You can measure the resistance of the plug caps w/a multimeter (as well as the plug wires) -- you can measure the coils (once you get the specs) -- or, you can just compare readings..... You can swap spark plugs around (assuming you haven't replaced them?).

One tip -- for a sure-fire way to determine engine miss due to lack of spark: get yourself an inductive pick-up timing light and hook it up to the offending spark plug wire -- and when the spark goes away so will the flashes of the timing light. Keeps flashing? -- something else is probably the culprit.....

Loss of spark is often load-related -- more load = more pressure on the ignition and any weakness/leak/low-voltage will make its presence known. Not so much, ime, just revs. And, if you want this from someone w/decades of experience and a well used coil-tester (who's charged many $$$ to guys who've brought their coils in to be checked) -- there are very very few bad coils out there.

A pretty-darn-good ignition checker is a spark plug with the grounding strap removed so that the spark must travel, in the atmosphere, (say) 3/8" to get to ground (side of the plug). Looking at that spark -- fat, blue, sharp spark -- will tell you alot. Or not..... :blink:

Good Luck

 

[dcarver]

Good to hear the local dealer treated you right. Your tech I'm guessing was Ivan? Kinda of tall and skinny, short hair? I don't have any suggestions, sorry..

 

[mtndragon]

Ivan was the one that helped, and I was very pleased with every aspect of the service. Powerhouse is a stand up dealership, and a pleasant change of pace from previous dealer/shop experiences. I am going to play with the plugs and wires some more in the morning before I do anything else I read in another post about someone that pulled all caps and trimmed wires, reinserting with dielectric grease with some success. I appreciate the responses and insight, and I will chase this spark more thoroughly in the morning.

 

[burnergold2B]

OK, here is my scenario. My questions are:
From anyone that has had a coil failure, are these the signs and symptoms?

Is it possible since the coil is firing two cylinders, that only one cylinder is not firing with a bad coil?

Thoughts?

Thank you.

Fuel filter is loaded with water/crap. Drain fuel and install new filter.

 

[yamaholic]

The coils fire 2 cylinders at a time, if I'm not mistaken. 1-3 and 2-4

Betcha it's the cap, lead to the cap, or a cracked plug. I would guess the plug. BTW, often the cracks are internal so you won't be able to see them.