Occasional engine hesitation

[Beemerman59]

Bike's an '08 GSA with 34K on the clock. Fitted with Remus headers, Akra end can, paper filter and has been remapped at Hilltop last year in that configuration. In the last month or so when on a neutral throttle, at low speed such as when dawdling along in congested town centre traffic, the engine will miss on one cylinder - enough for me to think the engine is about to stall and grab the clutch. Its at around the 2K-2.5K revs. It doesn't happen everytime, say about 1 in 4 times when doing slow speed manouvers on neutral throttle. This is making the bike a pain to ride slowly as I'm constantly waiting for it to happen and it makes for a very jerky progress through traffic when it does.

I cannot tell which cylinder it is. The engine runs perfectly when on the throttle its just at these low revs and on a neutral throttle i.e maintaining speed not accelerating. My GS911 is not throwing up any fault codes. I do my own servicing and the valve clearances were spot on last time they were checked (4K miles ago) as was the throttle body balance. If a Lambda was on the way out I would expect the GS911 to throw up a fault code but I don't think it would if it was one of the coils. First up I plan to give the bike a service even though its a bit early and put new plugs in. I'm also tempted to swap the primary and secondary coils over to see if that makes a difference.

Any other ideas?

 

[Bendy toy]

This was another symptom I had with a failing coil. Mine smelled burnt but still seemed to work. I replaced one and the other one failed a few miles later. At least that explained why swapping coils left-right didn't help much. They were worst in traffic when engine runs hottest.
Another possible is a crank position sensor. They can be fine cold but break down when hot. They often don't generate ECU errors.


Sent from my phone with mangled spelling

 

[Magwych]

Have you filled up at Tescos/Sainsbury recently? I have exactly the same model plus Hilltop remap and had the same symptoms. I tried using the Super flavours of fuel from the likes of Shell and Esso, which improved things a lot. A few shots of injector cleaner in each tankful has also helped. This does mot identify the cause, but does relieve the symptoms, at least.

 

[Beemerman59]

This was another symptom I had with a failing coil. Mine smelled burnt but still seemed to work. I replaced one and the other one failed a few miles later. At least that explained why swapping coils left-right didn't help much. They were worst in traffic when engine runs hottest.
Another possible is a crank position sensor. They can be fine cold but break down when hot. They often don't generate ECU errors.


Sent from my phone with mangled spelling

I don't have my manual handy but do you know if the secondary coils are the same as the primary's? I was thinking of swapping a primary coil with a secondary on the assumption (shouldn't really assume anything I know) that its the primary that has the biggest impact on combustion and more likely to give the symptom of a missfire.

 

[Beemerman59]

Have you filled up at Tescos/Sainsbury recently? I have exactly the same model plus Hilltop remap and had the same symptoms. I tried using the Super flavours of fuel from the likes of Shell and Esso, which improved things a lot. A few shots of injector cleaner in each tankful has also helped. This does mot identify the cause, but does relieve the symptoms, at least.

No, I usually use my local Esso's. It might be worth putting some injector cleaner in though as its cheap to try.

 

[G5RJO]

Primary and secondary coils are not interchangeable. Primary coils are straight, secondaries have a 90 degree bend and are also handed left and right.

Pull the secondary coils and inspect the bodies, in particular the machined in groove in the metal body. My coil had a rusty crack augie} never a nice thing to find eh?

My symptoms were very similar.

Roger.