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Discussion Starter #1
To update those who wondered about what the diagnosis was after my bike was overfilled with fuel. It was first flooded but then started, after which it ran fine for about 30 miles but would not restart after the engine was shut off.

The guys at the BMW shop say that the the vent line appeared to have some blockage and the overfilling may have finished plugging the line resulting in the flooding and subsequent plug fouling. When they replaced the plugs, the bike started, ran for a few minutes and then quit. When they do get it to restart, gasoline sputters out the exhaust leading them to think they have a catalytic converter and/or muffler drenched in gasoline. They are going to hang the exhaust over the weekend to attempt to dry it out, hoping to cure the problem (and to save themselves from the bomb blast).

Their question is whether or not that will cure the problem or if the catalytic converter is ruined and will require another (and a whole new exhaust system since it is integral).

Obviously I hate that prospect. Any words of wisdom on this subject?

In case replacement is necessary are their any used exhaust systems out there?
 

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Base from your thread, it looks like your cats are starting to malfunction. I think it should be replaced asap to prevent further damage on your car. That's what happened to me some time ago, so I have to change my BMW catalytic converter then...There's a lot out there with good cats...Good luck...
 

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2005 K1200LT
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Everthing esle aside, I don't see how the fuel got from an over filled tank to the CAT? It is almost impossible to flood a fuel injected engine unless the injector is stuck open. I would question the tech that made that diagnosis.
 

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Discussion Starter #6
Morley said:
If the converter got fuel soaked, it is shot.
They called today and said that they found lots of trash in the fuel filter yesterday, found some trash in the tank, the gas smelled weird and evaporated real fast in the container it was in overnight. I bought that famous last tank at a podunk place in mountains since I was not sure where next fuel would be. Maybe I got a tank of really bad gas that contributed to or caused the problem?

They said the engine runs fine now but do not know the status of the converter. How do you know if it is ruined?
 

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2005 K1200LT
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As long as the converter is not clogged (and they said it was running fine)- keep using it. You won't cause global warming. :)
 

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Discussion Starter #8
jzeiler said:
Everthing esle aside, I don't see how the fuel got from an over filled tank to the CAT? It is almost impossible to flood a fuel injected engine unless the injector is stuck open. I would question the tech that made that diagnosis.
I think the theory was that once the engine flooded and the plugs fouled (bad gas? clogged vent?), the continued efforts to start it, including my downhill bump start effort resulted in the fuel in the exhaust (and the crankcase). Being mechanically challenged I'm not sure but I think that was the idea.
 

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tumbleweed said:
They said the engine runs fine now but do not know the status of the converter. How do you know if it is ruined?
Once raw fuel gets into a catalytic converter it starts to break down the catalyst bed. Once this process starts it continues and can not be stopped or reversed.
 

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2005 K1200LT
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Ok Lynn, I can buy that explanation for flooding the engine.

Just remember that the CAT is a polution control device and unless clogged a bad one will not effect performance. The O2 sensor is ahead of the CAT.
 

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Morley said:
Once raw fuel gets into a catalytic converter it starts to break down the catalyst bed. Once this process starts it continues and can not be stopped or reversed.
I know it's not putting the environment at the top of the list of priorities, but has anyone with a bad cat ever just cut it out, and replaced it with an appropriate straight pipe? What's the general price on a new cat? dwillie.
 

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2005 K1200LT
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There was one that cut the unit open and tossed the broken, rattling cat substrate and welded it back up. You can only buy the entire system from BMW. The aftermarket units have no cat.
 

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Discussion Starter #13
Sheesh...this is becoming a nightmare. The tech says the bike starts and runs fine up until it gets hot to the point the fans switch on and then it dies. No fire, no spark. Says he has never seen anything like that and is stumped.

Any ideas?
 

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The Clymer schematic (as far as I can read it) indicates that the left and right fan motors are switched by a fan relay. Power from the relay to the fans goes thru fuses F9 and F10 in Fuse box 3. The fan relay also has a circuit that goes thru fuse F1 in Fuse box 1 that connects with the ignition coils on one branch and the Motronic on another branch (I think; the two-page schematic shows a line that is green/black up to the right margin on the left page, but no corresponding line from the left margin of the right page. Clearly an error in the schematic. Another green/black line connects the Motronic relay to the Motronic control unit at pin 1, so I assume the fan relay circuit is a branch.) So, one possibility would be that the fan relay is triggered by the motronic, the circuit is closed to the left and right fan motors, but at the same time there is a disruption in the circuit that connects the fan relay and the ignition coils.

Seems unlikely.

The coolant temperature sensor (AKA engine temp sensor) has a direct connection to the throttle potentiometer, and both the coolant temp sensor and the throttle potentiometer connect to the motronic. I'm guessing that the motronic sends a signal to the fan relay when the coolant temp sensor output indicates "too hot;" this signal turns on the fans. At the same time the motronic shuts down the engine, either through the fuel pump relay (shutting of the fuel pump) or through the ignition coils (which have direct connections to the motronic).

Question for the gurus: is there a fail-safe circuit on the LT that shuts the engine down if the temp goes above a predetermined point? If so, maybe that is being activated by erroneous info from the coolant temp sensor?

Otherwise you may be looking for a new motronic, unfortunately.

Added: Just re-read your last post. The tech said no spark when the engine shut down. Definitely coil related. I'd think about checking that fan relay before digging out the motronic.
 

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Discussion Starter #17
For any of you who are still interested in the conclusion to this tale, I will spare you the interim story and get to the end: It seems that the Hall sensor was defective and would shut down when the engine reached maximum temp. This behavior led to other theories but once it was replaced all is well.
 
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