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Chronic Fuse Blowing--Motronic?--Fuel Pump?.....aaargh....!


fasterwheels

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fasterwheels

Hi, not a frequent poster but got a wicked pissa' of a problem here on my 2001 R1100S. For the last 3 or more years I've owned the bike now (got it with only ~9k on the ticker) she has run as solid and reliable as a stone as long as I keep oil in her, and fresh rubber on her; she just LOVES to run!

 

However, recently now I keep blowing the #4 fuse on the left side fuse box which is, apparently, the "fuel pump, and Motronic" fuse. I have been trying to cover all my bases and fitted a new fuel pump, filter, recent 36k service w/oil, filter, gearbox, final drive fluids all changed, new generator belt; the whole nine yards. This fuse CONTINUES to blow. It is one of the 2 15amp fuses on that side. The other controlling some lights and horn I believe. There was just another bike like mine in the shop with a strikingly similar problem and was shown to have bad relays (among other things in rear-end wiring) so I also tried replacing all 4 mini-relays on the bike to (including of course BOTH the Motronic relay and the fuel pump relay).

 

In testing today, I just blew the fuse AGAIN (twice) while riding test-laps around Garden of the Gods. Seems to be no real pattern in the way it blows. Whether in lower RPM's pulling around and past slower traffic, cruising @ ~3kRPM through town or a back road, I can't put my finger on what in heaven's name could be doing this.

 

Given the new fuel pump, it would lead me to believe there is something wrong with the way my Motronic is working, or a wire somewhere in-between. I am at a terrible loss here as to how to go about fixing this. Has anyone else seen anything like this? My bike is in such great shape and running so beautifully that this just tears at me every waking moment of the day lately.

 

Any advice, insight, or experience would be MUCH appreciated, especially in leu of an $800 Motronic unit. Trouble-shooting the bike is obviously a better option, but right now I am at the end of my wick. Thanks in advance for ANY and ALL support here! Aaaargh...! --Jim

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ShovelStrokeEd

I'm assuming you changed the fuel filter as well and that could be the source of the problem. If you didn't change it, it could also be the source.

 

A clogged or backwards installed fuel pump will not pass gasoline properly. The fuel pump could be struggling to maintain line pressure and drawing too much current. The fuel pump is capable of pressures as high as 120 PSI and will (not so) happily do that to get to 41 PSI in the fuel rail.

 

Unfortunately, all the connectors for this stuff are under the tank and that makes it a PITA to check with ammeters or pressure gauges. The tank is probably going to have to come off anyway. More bad news, very few multimeters go beyond 10 Amp DC for measurements so you will need a independent DC ammeter. You can get one at any place that sells automotive gauges and they are relatively cheap.

 

Another possibility is harness issues. Carefully inspect the wiring leading to both the fuel pump and the Motronic. Look for chafing and/or points where the wire ties securing the harness to the frame seem to be just too tight. Try clipping a couple of those ties to see if this reduces the frequency of the failure. If so, you can probably go in there with some shrink wrap and a soldering iron and put things right.

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fasterwheels

Indeed I did put in a new fuel filter and I assumed that the mechanic that did it for me had the correct orientation. The fuse-blowing was even before that though. I had previously had a new fuel filter many miles ago when my fuel tank o-ring was replaced due to a small leak. So my next train of thought was with some of the wiring in the fuel pump if not the Motronic. Like you said, it is probably going to come down to tracing wires and testing currents, circuits, etc...

 

I guess either way it might be worth another check in the pump/filter assembly.

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BeniciaRT_GT

I was about to post to this, but saw you online...

 

Sent you a PM with my number...

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I'll take a closer look at the R1100S wiring diagram tonight, but one thing I'd try to see if it is a pump issue or not is put a fuse in-line with the power to it temporarily. One size smaller than the main one the pump is on. Say, temporarily bump the main one to 20A and splice in a 15A. Going to take a bit of fiddling to do, but it would help narrow it down.

 

The odds of a Motronic having an internal problem blowing a fuse, while not impossible, such is exceedingly rare. I'm betting more on a chaft wire in the harness somewhere.

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According to the diagram, fuse F4 feeds - a 'keep alive' voltage to the Motronic via a hard connection to pin 23, operating voltage to the Motronic via the engine electronics relay, to the fuel pump via its relay, and to the diagnostic connector.

 

That last one I hadn't thought of. Anything going on there? Laying loose such that a terminal of it could short out? Pinched wire, etc.?

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fasterwheels

Ken, thanks for looking into this in a little more depth for me. I don't know if I have any of that information in my maintainence manual. I will repost as soon as I can get "under the hood" a little bit after work this week. Lord knows I am itching to get back out on a ride longer than 30mi! I am expecting to find a mess of poorly/tightly rapped wiring of questionable quality.

 

And this may seem like a dumb question, but does the current travel through the fuse FIRST on its way to the relays and componentry or AFTER coming out of the relay? Just want to have an idea which side of the circuit I should be looking at. Component side?/Power side? Also, any thoughts on the wiring in the actual tank? i.e. to the fuel pump, low-fuel warning sensor, etc.? all that stuff in there seems hopelessly exposed to fluid dynamic, vibrations, weight shift and such. most of it is even exposed! Just seems to me like an opening for minor electronic niggles. thanks again, get back with exploratory findings soon. Jim

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However, recently now I keep blowing the #4 fuse on the left side fuse box which is, apparently, the "fuel pump, and Motronic" fuse.

 

Edit: just noticed you've got an 1100S, so the fuse box is different from the 1150RT. (I attached a diagram of the 1150RT fuse box, which I now realize isn't relevant to your question.)

 

Does the fuse that's blowing power any after-market accessories?

834491-fuse-box-diagram.gif.b6e412b38f94efdafba61df5198d51e1.gif

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does the current travel through the fuse FIRST on its way to the relays and componentry or AFTER coming out of the relay?
First.
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