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Discussion Starter #1
I have had a recurring problem starting my bike. Even the local BMW shop is baffled. The bike does not start when the tank is full or near full. The only way to get it to start is to turn the throttle while cranking the starter. Once the bike is ridden till the tank is less full, say a 1/4 tank down or so...no problem.

It started at the end of summer and has continued to haunt the bike. It was at the shop for two weeks before they finally drained the tank and took it to a station to refill the tank and, voila, it happened again. So the dealer finally believes my story but they are confused.

Has anyone dealt with this? :confused:
 

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Wrencher Extraordinaire
2005 K1200LT
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That is a new one for sure. I'll have to put on my thinking cap for this one. See if it is different with the gas cap loose and tight as a starting point and we will go from there. Does it matter if it is hot or cold? I presume you have ridden it to the station and filled up (on the side or center stand?) so it is warm and has sat for a short time while you filled it up. After she is starting ok (1/4 tank gone) try a stop on the same stand as if you were filling the tank, open the cap and then replace the cap and try to start.


I await futhur info...
 

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My 99LT needs to be cranked longer after a quick fuel stop when good and warm , I am guessing that the some of the fuel in the injector rail has turned vapor and turning up the throttle calls for more fuel than at idle and gets the vapor purged on through . Can you hear the fuel pump up and stop when the key is first turned ? it stops and is waiting for oil pressure to come up upon engine start .

Thats my guess and I am sticking to it . :histerica

Bob G
 

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Here's a guess.......
You may have a leaking injector which floods one cylinder when the tank is full and the fuel rail has more pressure in it. This would be comparing 1/2 full to full with the ignition off. Think of the tank as a water tower. Six inches of height in the fuel level probably doubles the pressure in the lines and fuel rail with the bike off. Strictly a guess. Try a tank with some Seafoam in it and see if that helps. Also check for the dreaded line split in the tank. I suppose the full tank could be distorting just enough to open the crack a little if it's in the early stages of failure.
 

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deanwoolsey said:
Here's a guess.......
You may have a leaking injector which floods one cylinder when the tank is full and the fuel rail has more pressure in it. This would be comparing 1/2 full to full with the ignition off. Think of the tank as a water tower. Six inches of height in the fuel level probably doubles the pressure in the lines and fuel rail with the bike off. Strictly a guess. Try a tank with some Seafoam in it and see if that helps. Also check for the dreaded line split in the tank. I suppose the full tank could be distorting just enough to open the crack a little if it's in the early stages of failure.
Dean,
water column height Vs weight is 1 foot = 1 PSI so your theory only adds around 1/2 PSI or less. Good theory but I doubt it is valid since the injector system runs at around 40 PSI (I think).

My 02 is also hard starting when warm and has sat for a few minutes while filling with fuel. Roll the throttle a little at usually fires up quicker. Don't have any good reason for this though.

Roy
 

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I noticed this on my 99 at times, but not always. First I attributed it to the charcoal canister, but after surgery to remove said canister, it still did it. Then I read a post here about a similar problem. Try to start, cranks for too long, STOP cranking, then crank again and wala, it starts right up. :confused: Nobody seems to know why, but it always starts right up on the second try so I have stopped worrying about that. :D
 

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Discussion Starter #7
Sorry to say, hot or cold, warm engine or cold, it cranks and cranks and never catches when the tank is full. It is not getting fuel into the cylinders. It is not flooded...no fuel smell and no rich exhaust when it finally does start. I turn the throttle WHILE cranking (which is said to be a no no by the BMW tech) and the engine sneezes violently. Then I crank it again with the throttle partly open and it grudgingly starts.

That's MY story and I'm sticking to it!
 

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To make sure I understand this fully, this happens on the very first start after filling? IE, starts fine, you drive to a station, fill up, and won't start right after filling?
 

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Discussion Starter #9
calvarez said:
To make sure I understand this fully, this happens on the very first start after filling? IE, starts fine, you drive to a station, fill up, and won't start right after filling?
Yep, this sequence of events is one of the times it has done it.
 

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Discussion Starter #10
Interestingly enought, I just talked to the dealer. They just got another LT they sold right after mine this year. with the same problem. They have put what is known as a PUMA in to the factory. Probably an acronym for Perplexing Un-diagnosed Mechanical Anomoly. :rotf:
 

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I am going to guess this has nothing to do with the actual filling of the tank, but the sequence of events that you go thought when filling the tank may be the key. Perhaps you only put it on the side stand when you gas up and the side stand switch is bad, Or maybe you only crank the handle bars to the left fully and that is causing some problem with the ignition switch. Or any combination of these and the added heat from riding to the station or cooling of the fresh gas.

You'll have to think way outside the box on this one. But who knows, I could be wrong also. Won't be the first time.
 

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Have you/can you try starting it before you put the cap back on? Would eliminate pressure being an issue.

When does the issue go away? IE, how low does the tank have to get?
 

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There's not too many variables. Air, fuel, spark, and timing. I'm still leaning towards a partially clogged injector. A big dose of Seafoam is a pretty cheap trouble-shooting option and it's real easy to do. It may also be caused by a bad reading from one of the temperature sending units which causes the Motronic to set the fuel mixture wrong. Filling the tank might just be coincidental as the sending unit heats up while it's being filled. You could try filling it from a five gallon can when the engine is cold to test this theory.
 

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Discussion Starter #14
tonygret said:
I am going to guess this has nothing to do with the actual filling of the tank, but the sequence of events that you go thought when filling the tank may be the key. Perhaps you only put it on the side stand when you gas up and the side stand switch is bad, Or maybe you only crank the handle bars to the left fully and that is causing some problem with the ignition switch. Or any combination of these and the added heat from riding to the station or cooling of the fresh gas.

You'll have to think way outside the box on this one. But who knows, I could be wrong also. Won't be the first time.
You are correct. Filling the tank is one of the times it has started to do this. It has been on the side stand and on the center stand and still done it. The dealer has hitched up gauges to test the fuel pressure in the tank and a myriad of other things.
 

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Discussion Starter #15
calvarez said:
To make sure I understand this fully, this happens on the very first start after filling? IE, starts fine, you drive to a station, fill up, and won't start right after filling?
Yes and no. This is one of the sequences of events that seems to be the most common start to the problem. It seems to run fine once started and starts with no problem once the tank is lower, say at 3/4. This may be a coincidence but????
 

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So let's make a list of what changes with a full tank...

Fuel is closer to whatever vent would be at the top. This should run to the vapor recovery canister. Then that runs to the intake to pull fumes.

There is less air space, so any vacuum/pressure condition would be much more noticeable.

Now what happens during the act of fueling...

If you live in a state with the vapor recovery nozzles, there's possibly some pressure being built up in the system?
 

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Discussion Starter #17
Tank pressure has been eliminated by the gauges that the mechanic put on the bike when they reproduced the problem. With a 6+ gallon tank that is never completely full, really, there is plenty of air in the top of the tank to balance pressure upon closing the top. Lack of pressure would be more likely as there is no fuel getting into the cylinders. Obviously there is no vacuum at the point of filling the tank and there surely is no pressure after the bike sits for a couple days. BTW - it continues to have the problem parked in my garage on the center stand.

From what I have gotten so far, the most like culprit is a faulty fuel sending unit. I am not sure if this is what some refer to as a "mototronic" but that has come up a couple times.
 

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So Steverino, get yourself some siphon hose and pull three gallons of fuel out of that beast to see what happens. I bet she still won't start.
 

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Have you disconnected the charcoal canister? This happened to me every time until I got rid of the canister
 

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Discussion Starter #20
deanwoolsey said:
So Steverino, get yourself some siphon hose and pull three gallons of fuel out of that beast to see what happens. I bet she still won't start.
The bike is under warranty and this is one of the steps the BMW dealer was pursuing next. FYI - I agree, I think it is a coincidence that the tank is full but it is confusing.
 
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