Engine Misses

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vroomr
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Engine Misses

Post by vroomr »

My '07 with 51K miles occasionally misses at idle. This started just before its recent service which included spark plug replacement, so we know the plugs aren't the problem. What might be causing this? Bike runs great otherwise.
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Re: Engine Misses

Post by Newportcycle »

Is it truly a miss fire or is the bike just running rough or stumbling a bit? Did you do the last service yourself? Do you or has there been any check on engine codes?
vroomr
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Re: Engine Misses

Post by vroomr »

It's a stumble accompanied by a momentary dip in rpm, per the tach. This started just before my recent service, which was performed by my usual dealer. Are codes are read as part of normal service?

When I brought it in it was due for plugs -- they had 25K miles -- and the service guy said let's see if that fixes things, which seemed reasonable.
Richard
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Re: Engine Misses

Post by Newportcycle »

Yes dealer tech would have scanned codes so I would assume that none were present. A sticky idle actuator maybe an issue. I believe that Don found an issue with his O2 sensors which caused rough idle. You might try searching this site for that thread.
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Re: Engine Misses

Post by vroomr »

Thanks. A search on this symptom, not bike or BMW specific, gave these culprits, in order of popularity: plugs, clogged fuel injectors, O2 sensors.
Richard
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Newportcycle
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Re: Engine Misses

Post by Newportcycle »

vroomr wrote:Thanks. A search on this symptom, not bike or BMW specific, gave these culprits, in order of popularity: plugs, clogged fuel injectors, O2 sensors.
viewtopic.php?f=20&t=30249&hilit=sensor

This thread may give you some hints.
vroomr
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Re: Engine Misses

Post by vroomr »

Thanks.

One other thing I noticed is that the roughness occurs right at engine start or very soon thereafter, whether engine is hot or cold. Today it stalled right after a cold start.
Richard
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Re: Engine Misses

Post by Newportcycle »

vroomr wrote:Thanks.

One other thing I noticed is that the roughness occurs right at engine start or very soon thereafter, whether engine is hot or cold. Today it stalled right after a cold start.
Without a diagnostic tool and observing their readings I don't know what to tell you. How long after a refueling did it begin? Possibly bad fuel or water in your fuel? You may want to try correct portion of fuel additive such as HEET which is to remove water, put in new fuel and see if that helps.
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Newportcycle
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Re: Engine Misses

Post by Newportcycle »

Vroomr,
You could try and rule out a faulty coil. Start by checking your stick coils for resistance, BMW does not publish the value range but checking both coils will tell you if one is significantly different from the other. Try to isolate the miss fire to one side, then you can try changing the coils with the other side coil and seeing if the problem switches sides as well. Good luck.
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Re: Engine Misses

Post by deilenberger »

I really think that trying to diagnose this without a diagnostics tool will become expensive, as lots of people have lots of ideas - and as usual - the one that fixes the problem (if there is one) will be the last one tried.

It's a case where either an independent with a diagnostics tool, or a dealer or purchasing your own diagnostics tool will be the resolution to the problem. If there is a miss - the only way to tell which cylinder it is - is by watching the O2 sensors to see which one drops voltage when the engine misses. There is no misfire recording in the ECU on the bikes (unlike cars), nor are there standard codes like OBD-II does for cars. The "home" tool you need is a GS-911 - once you have that let us know - perhaps we can guide you in it's use a bit.

Or you can shotgun it: Replace plugs. Replace coils. Replace steppers. Replace.. replace.. that gets expensive real fast.

BTW - when I had this problem on my '07 - it was an O2 sensor cutting out. The only way to ID that failure is with the GS-911 or the dealership computer. Or paying about $500 for a pair of new ones from BMW, or $80 for a pair of universal ones from Amazon.
Don Eilenberger - NJ Shore
2012 R1200R - I love this bike!
vroomr
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Re: Engine Misses

Post by vroomr »

Thanks, guys.

When I was out riding today I gave it wide-open throttle twice--twisted till I couldn't any more--in this non-wrench's belief from what I read online that WOT ignores the 02 sensor input and just spews fuel, in the hope that this would push out any clogs in an injector. I didn't break anything, but it's too soon to tell if I accomplished anything.

Other than the idle, the bike performs great. It was reporting 55-60 mpg on country roads, mostly 5th gear, some 6th.
Richard
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Re: Engine Misses

Post by vroomr »

Whether due to Motorrad Fuel System Cleaner, bad gas got used up, or whatever, the bike is now idling fine. In learning about all the possible causes, I now have a "how stuff works" question: Each exhaust pipe has an O2 sensor, but those sensors are downstream from an exhaust crossover pipe, so each sensor reads combined exhaust. Are the sensors' outputs averaged, or is that crossover just a mechanical brace that doesn't mingle the exhaust streams?
Richard
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Re: Engine Misses

Post by Newportcycle »

I'm glad your problem is solved.

SO, I'm no expert. I would believe that each O2 sensor reading is used to adjust pulse width on it's applicable injector, I cannot see any advantage to "averaging" these readings as your goal is complete combustion in each cylinder.

The "crossover" pipe, is to balance pressure waves and even out flow in the headers, I don't believe you will see combine exhaust flow in that pipe.

Here is an explanation of that crossover from Cycle World;
As the exhaust valve(s) of a cylinder open, a positive wave of pressure travels down the pipe. When it comes to any point of expansion (such as when it joins a collectors pipe, or when it reaches atmosphere), that wave of expansion also expands back up the pipe. If it arrives in the cylinder during valve overlap (exhaust not yet quite closed, intakes just beginning to open), it draws out residual exhaust gas in the combustion space and can even propagate into the intake system, causing intake flow to begin even before the piston has moved downward on its intake stroke.
Because positive and negative waves alternate in the pipe, at some lower rpm it is a positive wave that arrives at the cylinder during overlap. This reduces torque at this rpm by stuffing more exhaust gas back into the cylinder and into the intake ducts, thereby delaying the intake process. In motorcycles with carburetors, the positive wave also causes an over-rich condition, as the carburetor adds fuel to flowing air no matter which way it moves.
By providing another point of expansion, crossover tubes—which are often quite small—can broaden the rpm range over which the negative wave arrives during overlap, thereby improving cylinder filling and power.
vroomr
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Re: Engine Misses

Post by vroomr »

Excellent, thank you.
Richard
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