Help diagnose a misfire please

[dern]

Evening.

I have a 2005 R1200GS with about 31k on it that has developed a misfire in the last 100 miles. It manifests itself as an occasional misfire at idle (revs drop for a fraction of a second every 10 or so seconds) and a mild surging every few seconds while riding on a steady throttle. It's most pronounced on a steady throttle below 5000 rpm and happens in any gear. If I apply throttle the bike accelerates fine. It feels slightly lethargic at low throttle openings I guess but that might just be a trick of the mind. If I apply full throttle it takes off just fine. I have a full tank of fresh fuel and the problem started half way through the last tank of petrol and putting fresh in didn't change anything.

I've pulled the plugs and they look like this...

The plugs are from left to right... lower left, upper left, upper right, lower right. I've replaced these with new plugs and the problem is exactly the same.

Given that the misfire is fairly steady but intermittent and there doesn't seem to be a problem with getting fuel in and replacing the plugs didn't solve the issue my next thought is coils. This is obviously where it gets more expensive so thought I'd see if I was on the right track.

It looks to me that the bottom left plug is quite a bit blacker than the other plugs. The two centre plugs are identical and look fine and the lower plug on the right looks darker but also ok. The bottom left one is a bit sooty around the base which would be (in my opinion) in line with that plug misfiring over the last 100 miles.

If you agree that the next step is the coils I need to buy either just that one or all of them and either new or second hand. Are the coils the same for all years?

Many thanks,

Mark

 

[bisbee]

Mark
Do a search on here Read anything Steptoe has posted about swapping the coils etc

 

[dern]

Found this one...

Simple test.

Unplug the connectors that attach to the coil sticks each side on the bottom coil/spark plug. Go for a ride running on just the top two plugs. Does it ride ok ?

If so reconnect the connectors into bottom coils and disconnect the top connectors on each side. Then go for a ride running on just the bottom plugs.

If you suspect they're breaking down under load that's the perfect way to test them. If one or two are that bad you may even have trouble starting the bike and getting ti to run.

That's very clever, hadn't thought of doing that and will try that before rushing out to buy any parts.

Thanks,

Mark

 

[bisbee]

Found this one...



That's very clever, hadn't thought of doing that and will try that before rushing out to buy any parts.

Thanks,

Mark

Keep us informed old chap

 

[Bendy toy]

My money is on a failing coil. My 08 had similar symptoms. One coil failed then very soon after the other one went down.
I did the Steptoe test with no obvious change. But as both coils were wonky it's not too surprising.
The older black body coils smell burnt before they totally pack up.


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[dern]

Disconnected the bottom coils and runs the same... Still get the surging. Disconnected the top coils... Runs rougher as youd expect and surging still there. Any more ideas?

Thanks.

Mark

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[dern]

Removed the accelerator module, changed air filter (had one and thought I may as well) and reset the TPS. No change to any of these.

Surging is still subtle but very annoying, still feels like a misfire but the plugs are new and it's still there regardless of which pair of coils I'm using.

Don't know, think it might be dealer time. Hate not fixing stuff on my own bike/car but don't know the bike well enough to understand what could cause it and don't want to go down the swap parts route.

Cheers for the advice give anyway.

Mark

 

[dern]

The two dealers local to me are on 3 week lead times and I need the bike sooner than that. Does anyone else have any ideas what I could look at? I'm confident with the tools but don't know the bike...

Thanks,

Mark

 

[Bendy toy]

Swap the top (primary) coils left/right. See if the dirty spark plug moves. Ditto the plugs - one could be faulty.

Don't be tempted to change lambda sensor until sure it really is the cause.

A dealer should be able to lend you a used a pair of used but known to be good primary coils. They tend to fail in pairs so the usual left-right swaps can be misleading.


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[dern]

Given that the surging occurs when both primary coils are disconnected and running on just the secondary coils doesn't this preclude the primary coils as the cause of the problem? I'm not trying to question your advice, just trying to understand why you think it might help.

Thanks,

Mark

 

[Bendy toy]

Mine had similarly confusing symptoms. I decided the coils were ok and changed the badly sooted O2 sensor. It seemed fine for a few miles then went right back to its 35 mpg misfire.
But by now, one coil was smelling burnt and the bike was now a single banger. 5 miles down the road it went back onto one cylinder. This time the other exhaust was cool.
I went straight back to dealer and bought another coil. He said oh yes they often fail as a pair.
Problem was solved along with a bank account lighter by double what it should have cost. The Lambdas cost Megabux.
Too late I found out there are cheaper options made by same manufacturer. But I probably didn't even need a new sensor.


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[Bendy toy]

Of course all this is guesswork and conjecture but hopefully you'll avoid the same hassle if indeed yours is a coil problem.


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[dern]

Just in case it helps someone else...

I adjusted the valve clearances and the rocker arm end play. Most of the valve clearances were too tight. I also slackened off the throttle cable as it was too tight and there was no slack at all. Finally I synced the throttle bodies using a home made manometer as they were quite a way out too. The surging has now gone and the bike is running a lot better.

Cheers,

Mark