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R1100RT-P Misfire Sage continues


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Hi all,


As some of you have seen previously i am still trying to get to the bottom of my misfiring.


This is a UK model without Cat or O2 sensor - i have a CO Pot (Idle pot). The bike has been wintering outside and i have started it every week to top up the battery, it starts first time with no choke and it runs but with a sluggish idle.


I ran it tonight (very dark winters here in the UK) and i noticed that the left hand exhaust is glowing dull red where the right isnt at all? Could this be pointing to why i have a misfire?


So far in the cheapest way possible i have done the following;-


Full 28k service incl Fuel Filter.


Replaced Ignition Coil

Both HT leads

Both Plugs Brisk

Checked setting of CO sensor

Checked output of the Temp Sensor

Serviced cables

Serviced Injector assemblies

Replaced Oil Temp sensor for EFI (Top Block)

HES replaced

Timing set

New Battery

Replaced both injectors (New)

Set Zero-Zero TPS voltage

Techlusion Unit


All to no avail!


Anyone have any more suggestions?

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Afternoon Caerleon


The pipe color difference could be telling us something, but keep in mind just a little air flow across one side pipe can change it's glow color to not match the other side.


I see you have a Techlusion?-- I would definitely disconnect that as a test (don't just shut it off, discount the injector pig tail connection. I have seen those (usually early units) get moisture in them & cause all kinds or runability issues.


Otherwise run a compression check & verify no loose valves in their guides.


You might also verify no exhaust leaks letting air into the exhaust at low throttle opening.


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I have run it both with and without techlusion unit and no change - if anything it helps with going slower in traffic than without it.


Airflow was the same at the time both sides of the bike.


Compression checked and both left anf right are about 130-140 which according to the book is very good.


The valve will need a head removal?


Exhausts are perfectly sealed up - as ever its something i dont think i would have thought about.


So could it be running richer on the left than the right to cause a hotter exhaust?

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Afternoon Caerleon


You don't have to remove the heads to check the valve to guide for general looseness. To get a precision measurement you need to remove the valve springs & depress the valves just slightly but you should be able to just pry/move the valve top sideways & if excessively loose in the guides that should show up.


On your pipes, they should run a dull red with no air flow across them so the one that is not glowing either had a bit of air flow (even light wind) or isn't making as much heat (could be real rich or real lean), or sucking in air from a gasket leak.


Any chance you have a bit of water in your fuel tank?


How about fuel pressure? Just remove the fuel return line & see if you are getting any retune fuel to the tank. Is so you probably have enough fuel flow/&/pressure. If not then look for a pressure line leak inside the fuel tank.


Also, as a test you might try disconnecting your idle trim pot (just unplug it) that will richen your idle & very low throttle area. If that improves the miss or makes a difference that might give you a direction to look in.


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I have drained the tank and cleaned it ages ago when replacing the fuel filter.


Pressure is about 3 bar on the return line and it works all the way upto 80mph (Italian de-coked).


I tried the removal of the Pot this puts it in 'Get you home mode' i.e richer and i still have misfiring its been from really rich to just above really lean and no change.


All the wiring has been tested according to the haynes manual and nothing found apart from a stray earth to the ECU body, but this didnt make any difference.


I must admit i am beginning to think i wont ever find the root cause of the issue. To take it to BMW here they wanted £120 an hour just to look at it.

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Afternoon Caerleon


If you didn't find the problem is ALL you have done then your BMW dealer sure as heck won't find it easily (or at all) either.


I can give you ideas until the cows come home but that could easily have you chasing things that have no impact on the problem.


Can you give me (us) more detailed info on your misfire? Like real explicit, & at what RPM's it appears & what RPM's it doesn't. --ANYTHING that can help us experience the miss over the internet--


Is it there right from cold start or get worse when warm?


Can you actually feel the miss or just hear it?


If you can feel it, is it there in all gears?


Without being there & hearing it (the miss) in relation to the engine stabilization, load, throttle reaction while missing, feel on throttle crowd, decel loading, etc you will have to be the eyes, ears, & seat of the pants annalist, then convey that to us in words.


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  • 1 month later...

hi did you find out what was the cause of your misfire?

I'm having a similar problem misfire when warm. checked plugs

and changed them, fitted another coil. checked exhaust for leaks

couldn't find any. ticks over fine when could but as it warms up

the misfire gets worse. checked the valve clearances and rechecked they are ok. my bike is a 1995 r1100rt no cat or O2 sensor.

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I think its easier to just post some clips of the misfire at tickover. See below.


While riding the bike, it does misfire at all ranges and very noticable on corners which upsets the bike as if i have just hit a patch of oil.It happens in all gears and speeds, from cold to hot.


I have replaced the TPS sensor and reset it - One thing i have noticed is that even thou you set the TPS voltage to say .390-.400 mV (I'm not that far off Sea Level here)once you remove Fuse 5 for 10 secs to reset the moronic - i flip the throttle to re-learn to throttle limits and it resets the TPS to .375 - .380? Is this normal or indeed correct - it did it with both TPS.


I have done the Zero-Zero also since i last updated and it has not had any affect. I have managed to get it smoother, by turning down the mixture - but the misfire is still present.


I have borrowed a PICOscope which is a laptop run Oscilloscope checking the Kv f each plug wire which measures 6-9Kv

Hopefully these vids will get it across.


Thanks to all for helping me!



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Afternoon Caerleon


Your 2000RT has the Ma 2.2 Motronic so there IS NO TPS relearn like on the 1150 with Ma 2.4.


Removing fuse 5 does nothing for TPS relearn. That is what it is after you re-set it. The slight change after snapping the throttle closed is pretty normal on an older bike with slightly worn throttle shafts & some coking in the throttle bore.


Your You Tube links are dead (at least when I tried them).


Are you SURE it is actually misfiring or do you just hear a misfire like sound coming from the exhaust?


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Links should work now.


Yes, it does hear and feel like a misfire as if the ignition timing was wrong - but this is of course controlled by the moronic and that is the only thing i havent replaced/exchanged while the part is not cheap here i can pickup a second hand one close by.


I use the bike daily to get to work and have to live with what i have going on with it, but i would prefer to get it sorted once and for all.


When i checked and stripped down the TB's i couldnt find any wear on the butterfly shafts or any coke in the TB after i stripped, cleaned and ultrasonically cleaned them (at work).


I can understand diagnosis from across the pond is nigh impossible, but i have i think tried everything i can think off as a supposidly 'qualified person' to more reliance on those who know these machines and better understand them - i dont think i have a lot of options left.


Thanks for the assistance.

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Afternoon Caerleon


OK, just got one of the videos to work.


Try unplugging your Co trim pot to see what effect that has (should richen the idle).


If that does or doesn't change it might give us a direction to look.


Lots of carbon on the rear of muffler, have you been riding it a speed much or just a lot of idling.


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I have tried with and without the CO pot and with and without the Techlusion (in the other vids). I run it upto 70-80mph if i take the Motorway home or 20-50mph commuting thru the worst of London traffic. The CO pot has been checked and it is set to 2-3% CO (without CO2 pot the moronic defaults to 1.8% from what i have read elsewhere). I have checked the inside of the baffle on the exhaust as mentioned by someone and its solid. Changing the mixture only causes it to overheat - no mixture changes i have carried out have an affect on the misfire, so i run it slightly rich to avoid a lean miss.

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Evening Caerleon


With all you have done & checked you are getting down to the oddball things.


So I will give you some other possibilities to look into--


Like heavily coked up valves (on inside of valve head). See the below pix of what I'm talking about. When they get like this the intake fuel can get caught by the coking then drip into the combustion chamber. Those large drops of fuel don't ignite properly a light throttle or idle.


In line with the coking or poorly atomized fuel-- if you have coking on the backs of the exhaust valves you can get poor exhaust flow out of the cylinders. Keep in mind that the BMW 1100 uses a lost spark ignition, so you get a spark at EVERY PISTON up even on the exhaust stroke. If any burnable mixture is left in the combustion chamber on the exhaust stroke that spark on exhaust stroke can ignite it & it will pop directly into the exhaust system.


If that RT-P idled a lot during police service it could have lots of carbon on the valves. That intake coking mainly comes from oil going down the valve stems past the seal & guide on a hot valve.


Next, would valve lift & valve timing, a worn camshaft lobe can lower valve lift as well as alter valve timing (not saying you have that but something to check out).


Same with camshaft timing in relation to the crankshaft. Verify the cam timing is correct.


Have you sniffed the engine oil? Years ago I worked on (a non BMW) that idled terrible & popped & farted at low speeds. What I finally found was the oil diluted with raw gasoline. As the engine heated & idled that fuel would turn to vapor & come up past the piston rings.


Low fuel pressure can alter the fuel air mixture but can also cause the fuel injectors to give a real poor & lethargic spray pattern.(just something to maybe check).



Maybe put a timing light on it to see if you have a dancing low RPM spark advance. The 1150 naturally does this but the 1100 should be pretty stable. If the spark timing is dancing all over maybe look into a HES issue or loose trigger cup.


Check the voltage at the fuel injectors & ign coil. Low coil voltage isn't as bad a low injector voltage though. Low injector voltage can cause all kinds of fueling issues (especially at no engine load).


I presume you have already put fresh gasoline in it?


More, but this is enough for this post.


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Thanks DR.


I will try and find time this weekend to check if the intakes look anything like you have shown as what you say about the bikes service makes alot of sense and it cannot harm it to check.


Just checking with a local independant to see how much a head recondition will cost.


Thanks hopefully one more step forward!

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  • 1 month later...

I have had the bike apart this weekend and replaced all the cables (now they were expensive!). I used silicone grease on everything and brought a new bowden box - everything setup ok and set idle and 3000/5000 revs - still the misfire.


Rode it to work this morning it seems a little more happy to be accelerated, but i dont think i set the clutch correctly so going to do that later.


I replaced the coil while i had the tank off as i found a crack on the potting under the last one on inspection. On thing i wanted to check was the LT cable (Primary Coil input) on the manual it shows 3 wires going into the coil, but ony 2 connections? I buzzed and checked the resistance of the wires to the manual seems all ok. Then i tested the input voltage i get 11.9v at key/kill switch on, but when cranking i get 9v - does this seem to be right? I haev checked the BMW manual and cannot find any ref or schematic for it.

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Afternoon Caerleon


Your coil voltage seems just a bit low but that probably isn't your misfire. 9v cranking is on the low side of normal but again within reason. You need to test the coil supply power with the engine running as that is where your misfire is.


In any case, low coil power (& output)) shows up first under higher engine RPM's & higher engine load.


That 3 wires your manual shows going into the coil is basically 12v (13v-14v running) power in, & low side out to the Motronic coil driver (2 wire connector), & coil's ground connection to frame (mainly for TVRS suppression).


Can you feel the misfire while riding or just hear it? If you can only hear it then look for a possible leak in your exhaust system allowing air into the system causing internal popping.


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The outside storage during UK winters concerns me.

That is asking for corrosion in the humid, moist air. The misfire during lean angles suggests something related to ground (earth?) is moving around.

I once owned a Honda CB750 that had an intermittent miss from the 2 and 3 cylinders. It tuned out to be corrosion where the coil attached to the frame.

I'd review a wiring diagram and check/clean your grounds related to the ignition.

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I have the miss upright at traffic and while riding at all angles, worse is the feeling while getting my knee down for corners at speed =) it feels like the rear is stepping out. You hear it and feel it. No leaks anywhere to be found and i have stripped the bike down to clean all earths and checked resistances and everything seems fine.


Upflying living on a tiny island like ours your right it isnt good for anything outside 7 months of the year, but then these bikes are designed to survive these conditions and worse - Germany is similar in weather.


I would like some advise if someone has used a oscilloscpae type of test equipment and if they would list a logical step by step list of tests to make.



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Evening Caerleon


Well, you have put enough new ignition components in that thing to pretty well eliminate common ignition problems. If you do still have an ignition problem it is more than likely Motronic related (like coil or injector driver or Motronic internal anyway). Can you borrow a known good Motonic as a test?


That leaves fueling issues like low fuel pressure or low fuel delivery. You might try rigging up a fuel pressure gauge to view while riding the bike. Or at least cobble in a clear hose in the return hose to verify you have returning fuel while the misfire is present. No return fuel flow means either low pressure or low delivery.


Or, it leaves mechanical issues like cam lobe wear or cam timing or partially plugged exhaust valve ports. Are ALL valves opening about the same distance?


Have you run a compression test to see if enough compression & if somewhat even side to side?


Basically IF you have a good compression, good air flow into & out of the engine, stable spark with enough KV to fire under compression at the correct timing, & a good combustible fuel air mixture, then it should run good without misfiring. You need to find what it is lacking during the misfiring.


Can you get it to misfire without riding it? If so then maybe make up a spark viewer setup. To do that, get a couple of old (metal core) spark plug wires, then cut the wires in half & trim the insulation to leave about 6mm of wire exposed out of the outer insulation, then push each end of the cut plug wire into a tight fitting clear hose leaving a 2mm gap between the metal inner wire ends.


Then plug one of those spark viewer wires in each side between the plug wire & the spark plug top.


Now run the engine in a dark location (or at night) & watch the spark as it jumps the 2mm gap. Make sure the spark is constant & bright blue in color & doesn't skip a few sparks when it misfires.


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