Misfiring 2018 Speedmaster

The Workshop
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Half hour into today’s ride I noticed the engine starting to misbehave. It lost most power, didn’t want to rev, and engine sounded all ‘wrong’ and felt more vibey. I guess it was a bit like when you open the throttle when in too high a gear. There were no engine warning lights so I decided to start limping the 15 miles home.

The engine wasn’t running erratic, i.e. was consistent in it’s sound and feel, except occasionally for a few seconds it would suddenly surge and go back to normal before reverting to bad running again. First thing that sprung to mind that it might be running on one cylinder, due to bad spark or fuel injector on one side. Was hoping that when I got home and pulled the spark plugs I would get a clue. Annoyingly, about a mile from home, when in heavy traffic the engine start running mostly OK except for the occasional reversion to bad running. The engine was hot and fan running due to being in traffic, so perhaps engine temperature helped the ignition to ignite?

Anyway, below are photos of the spark plugs which I pulled after letting the engine cool; though as I said, it had been running mostly fine for the 5 minutes before getting home. The one with the masking tape around it is from the right cylinder and appears to have more soot around the insulator and side of the outer conductor. Presumably from unburnt fuel due to too high a fuel/air ratio or incomplete combustion due to weak/late spark?

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When I replace the spark plugs I did notice that the cap on the right side wasn’t as ‘grippy’ so perhaps the connection isn’t great. Though using a torch and magnifying glass didn’t show anything different on the inside of that connector.

I restarted the engine with TuneECU connected and it seemed to run fine when idling and revving it. TuneECU shown the manifold pressure on both sides was essentially the same, and about what I remember from when doing services, so I think the ‘air’ part of combustion should be OK.

I’ve had mild poor running in the past that went away after telling the ECU to forget it’s ‘adaptations’. So what I’ll probably do is go for a test ride another day and if/when the problem re-occurs pull over and reset the ECU adaptation to see if that changes anything. I can also wiggle the spark plug caps whilst riding along to see if that affects anything. (Though I think I did that today.) Finally, I can take my spark plug spanner and when the problem re-occurs kill the engine after and minutes of bad running a pull the plugs for a look.

I’m really hoping problem is with the spark and not fuel, though one easy fuel job is to look at the electrical connectors to the injectors, as they may well be corroded. (That’s have to wait for another day now).

Whilst on the subject of fuel, I did think to try loosening the fuel cap in case tank breather tube was blocked. Oh, I guess the fuel pump could also be a bit iffy.

Then there’s the potential for ECU getting confused by dodgy sensor like air temperature and air pressure, maybe for my test ride I should attach my spare phone to handlebars and have it connected to TuneECU so I can see what those sensors say.

All for another day…

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It sounds like you have a good plan for diagnosing. Things do seem to get complicated these days with sensors that determine the injector duration along with fuel pressure etc, then you have the good old electronics such as the coils, ht leads, igniter and crank sensor.
Hope you can find the culprit and build back the trust.

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You might just be lucky and have a duff plug. You could try fitting a new pair of plugs before anything more complicated. It worked for me last spring. :crossed_fingers:

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It did occur to me to swap plugs, I do have a spare pair, but I wanted to reproduce the problem before changing things so I can be sure the change I did was the cause. Guess I can add the new pair in the stuff I take on my test ride. :slight_smile:

Though for the paranoid, if it’s something like the coil being on it’s last legs, then new plugs may be enough to get it to work, for now, only for things to go wrong again later at a more inconvenient time when the coil deteriorates more.

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Yep, that’s what I think happened to me, bike running poor, swapped plugs, OK for a few hundred miles then fault came back. Turned out I had a coil that passed static tests fine but was failing when hot. Swapped with new and it fixed the problem. Thing is when my bike was hot in traffic (fan had kicked in - older trophy) it got worse whereas yours improved!
I had a look thru’ tuneecu and it does seem to have the ability to see the values of a lot of your sensors so I can see why you’d want to use that first.

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Maybe it would be worth taking an infrared thermometer with you to check downpipe temp? It helped me track down a faulty HT lead.

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Good idea about temperature check. A few minutes after I was home I did a touch test on exhaust to check if both felt the same. Not very scientific, especially as the exhausts are connected under the engine. It did occur to me to get out my multimeter which was a thermocouple to measure temperature, but I didn’t. I will add that to the pile of stuff I’ll be taking on my test ride.

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A duff ht lead can be more problematic in the cold, damp winter… could improve a bit when dried out by engine heat

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Hope you get it sorted mate.

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Thanks. I’ve already checked to make sure there’s Triumph dealers in northern Spain (there are) as I really don’t trust bike for the two weeks I’ll be there in May.

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There are dealers there mate. Don’t worry too much about it, just enjoy the journey! @Wessa and I had a brilliant time in northern Spain.

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So, today’s 3 hour sunny test ride was uneventful, bike worked flawlessly :smiley:

Before setting off I fumbled around under tank to check coil and fuel pump connectors weren’t loose. Though thinking about it now, I’m happy the problem can’t be the fuel pump because of the bad running jumping instantly to good running then back; fuel pressure isn’t going to jump up and down suddenly.

After starting the engine before setting off, I pulled off the right spark plug cap as a test and the struggling to idle and not wanting to rev feeling felt similar to how the engine behaved the other day.

I have a hypothesis that the bad running was cause by a bit of water getting down into the spark plug well, not enough to cause a problem initially, but after half hour of riding the engine heat could turn it to steam where it could permeated the cap and let the HT voltage leak. Then the bike fixing itself at the end of the ride could be the heat finally driving off all the steam to the atmosphere.

This seams plausible because my bike shelter isn’t complete weatherproof and I know the right side of bike had water drops on when I got it out. Also, I noticed that the ribber boots on the spark plug caps are rather warped, presumably from engine heat, so would be making a less than ideal seal.

So, my plan it to get new caps and fit new sparkplugs and not worry about things again until problems manifest…

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That sounds promising. Good luck.

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