Very occasional misfire when cold

Motocod · Post by **Motocod** » Thu May 21, 2015 7:52 am

Only happens when cold. Any thoughts?

Wondering if it might be a stick coil on the way out - they were a little bit rusty when I pulled them out a couple of months ago, so probably original. Or TB synch required?

Getting a bit nervous, as I'm off across France and Spain in three weeks time, so feeling super paranoid!!

Nik

Tapio · Post by **Tapio** » Thu May 21, 2015 6:26 pm

First thing to test: when it happens, keep the engine on high idle and grab both exhaust pipes with your hands. If it's a stick coil on its way going south, then the pipe on that cyl will warm up slower.
Obviously, you can only do this att startup, and you don't have many seconds to to do it.

Next test: take out a spark plug and put it on the cyl, with stick coil on of course. Take off the injector. Crank the engine. If both the spark and the injector is working intermittently, then it might be the hall transducers.

Motocod · Post by **Motocod** » Fri May 22, 2015 12:10 pm

Thank you, that's really very helpful - much appreciated.

I should mention that this happens incredibly rarely, and only when the bike is cold. It also seems to idle slightly lower than it used to - perhaps it's just that the TBs need balancing. Runs perfectly on fast idle.

Nik

Motocod · Post by **Motocod** » Sun May 24, 2015 12:03 pm

As an aside, after returning home yesterday from a long ride (450 miles!) I noticed that the bike varies between running on idle at 1200rpm and then dropping down to 1000 every couple of seconds. It'll do maybe 3 seconds at 1200, then 2 seconds at 1000, and it repeats very regularly. Odd!

I also noticed on the motorway at a constant speed that the bike sometimes feels like it very fractionally loses power. It's almost imperceptible, so hard to know what it could be.

JamesL · Post by **JamesL** » Wed May 27, 2015 11:59 am

Having been let down by Hall sensor failure twice I guess I'm scarred, but your symptoms could well be the start of the unit failing. Both times for me it started by intermittent short (almost unnoticeable) bursts of poor running, then finally let me down terminally. The first time (on the RS) it eventually died one February night on the M40, terminally. The second time (on the GS) I caught it before it died forever and was able to nurse the machine home on 1.5 cylinders and lots of bad language. Took it out at the weekend and then it took an hour of riding it up and down the lane (and getting the engine good and hot) to get an error on a GS911 diagnostic, so it will bluff you as long as it can before dying somewhere dangerous and inconvenient.

If I recall, a new unit is ~£120 or so - buy new or properly refurbished, as s/h it might last 5 minutes or 5 years. It's straightforward to fit and commentary indicates that it's relatively insensitive to getting the timing wrong if you don't have a GS911. You can replace it by the roadside, but better might be just to slap in a new one before you go.

Hope this helps, James

Motocod · Post by **Motocod** » Wed May 27, 2015 12:30 pm

Thanks James, I'll look in to that. Appreciate your reply.

Motocod · Post by **Motocod** » Wed May 27, 2015 12:59 pm

Wish I wasn't such a serial worrier when it comes to my bike! I'm sure it'll be fine, but I'd be so pissed off if I break down on holiday. I could spend hundreds replacing stuff just in case, so chances are I'll just go with it and see what happens...

metropolis2k · Post by **metropolis2k** » Wed May 27, 2015 1:04 pm

The random idle issue you has sounds like it could be a stick coil. Fortunately there's a really quick and easy way to test this while it's idling. I had a slightly lumpy idle too on my first S (the one you saw) and Steptoe did this test in front of me but found the coil was fine, it was just the throttle bodies were really out of balance (whoever had done it before did it wrong).

Originally posted by Smudger here: viewtopic.php?t=19343&sid=f34cb8c006923 ... 9b0d73f771

Run the engine till warm. Be VERY CAREFUL in the next few steps, as the exhaust will obviously be hot!!

Expose the connections to both the primary (main) and secondary (underneath) coils (small black connectors).

Familiarise yourself with the small electrical connecter on the coil, i.e. how to unplug it easily. At first it can be tricky, but like anything once sussed its easy.DONT PULL THE STICK COIL OUT!!!! THE CONNECTOR YOU ARE PULLING IS A 12v SWITCH ONLY, NO CHANCE OF A SHOCK FROM THIS BUT IF YOU PULL IT OUT YOU WILL GET A SHOCK!

With the engine running at idle, disconnect the secondary (the one underneath).

If the engine stops straight away, the primary coil on that side is goosed.

To explain this, the secondary coil fires if the exhaust emissions are high, to sort of clean them up. If the primary fails, the engine control unit will notice a higher than usual HC reading at the O2 sensor, and fire the secondary. It will do this continually, hence the reason why most coil failures are not easy to spot as the engine controller just takes over!

The secondarys are fired up to 60 degrees past TDC hence the reason why the 'stutter' occurs at high RPM, the engine speed almost makes it impossible for the engine management system to catch up!

JamesL · Post by **JamesL** » Wed May 27, 2015 1:37 pm

Motocod wrote:Wish I wasn't such a serial worrier when it comes to my bike! I'm sure it'll be fine, but I'd be so pissed off if I break down on holiday. I could spend hundreds replacing stuff just in case, so chances are I'll just go with it and see what happens...

+1 on the worry front! So long as you don't absolutely have to be somewhere by a deadline I'm sure it will be fine - all part of the Holiday Experience... 11xx Hall sensors are almost a consumable item - I think they all go at some stage and some people simply keep a spare on board. So if you lash out on one it's unlikely to be totally wasted and you can always flog it on Ebay. If the stick coil test and TB sync are both good, personally (as a fellow worrier) I'd lay in a spare Hall sensor. If you don't fit it beforehand you can have the fun of doing it at the roadside!

Motocod · Post by **Motocod** » Wed May 27, 2015 7:02 pm

We kind of have a deadline with our trip - making it across France in time to see the MotoGP in Barcelona! Leave Roscoff Friday morning, and planning to be at the circuit in time for Saturday afternoon qualifying...!

I'm going to do a throttle body synch and see how that affects things. Really I should have done it after the recent service (including valve adjustment), so it's possible that's causing it to run a tiny bit off colour.

metropolis2k · Post by **metropolis2k** » Wed May 27, 2015 8:57 pm

If the valves have been adjusted the throttle bodies will definitely need balancing. Hopefully that's it.

nab 301 · Post by **nab 301** » Thu May 28, 2015 10:48 pm

Motocod wrote:I also noticed on the motorway at a constant speed that the bike sometimes feels like it very fractionally loses power. It's almost imperceptible, so hard to know what it could be.

Just to confuse you completely ,
Could be any of the above especially TB balance, causing surging especially on smaller throttle openings, although my single spark version had something similar a good while back , cured by replacing the Lambda sensor... . That was at 75 k miles and I used a s/h lambda , now 110 k miles and the problem is occasionally reappearing again.

Motocod · Post by **Motocod** » Fri May 29, 2015 7:44 am

Thanks Nigel (and others!). I'm inclined to think this isn't something electrical, as the bike has only done approx 21k, so it seems a little early for something to fail.

Carbtunes should be arriving today or Monday, and while I do that I'll try pulling the lower plug leads to check the stick coils. Though to be honest I'm feeling confident the TB synch will make a big improvement.

Nik

Motocod · Post by **Motocod** » Fri May 29, 2015 7:15 pm

As per my other post, now seems absolutely spot-on following the TB balance. Result!

Nik