Fuse keeps popping! HELP!

[Tri]

I just purchased a 1998 1200c and the previous owner said the bike would not start. I have been trying to start it for a couple of days now. I have been pulling my hair out trying to figure this out. I narrowed it down to a 15amp fuse. Every time I push the ignition start button the 15AMP fuse keeps popping. Does anyone have any idea where to start?

 

Thanks.

[AnotherLee]

Tri - welcome.

 

Even though it's called a 1200, the 1200C is actually an oilhead. I know, it's confusing.

 

If you don't get any answers here, you might try the Chromehead forum. Do you have any experience reading electrical diagrams?

[Skywagon]

others with more expertise will jump in, but if happening when you hit the starter, I would try first to push start the bike. It's not that hard to do if your battery is strong. Just get some help and pop the clutch in 2nd or 3rd. Sounds like the starter may be putting high load on circuit. Not quite enough in your post to figure out. When you turn on the key and the fuse normal, can you turn on other things light lights, horn, signals, etc without popping fuse.

 

BMW starters tend to get gunked up over time and can drag created electrical load.

 

[Tri]

The bike turns over, but no spark . Fuses keep blowing

[mneblett]

others with more expertise will jump in, but if happening when you hit the starter, I would try first to push start the bike. It's not that hard to do if your battery is strong. Just get some help and pop the clutch in 2nd or 3rd. Sounds like the starter may be putting high load on circuit. Not quite enough in your post to figure out. When you turn on the key and the fuse normal, can you turn on other things light lights, horn, signals, etc without popping fuse.

 

BMW starters tend to get gunked up over time and can drag created electrical load.

Afraid the starter is not on a fused circuit. The starter solenoid, the starter relay and the starter switch, on the other hand, are. First thing I would do is inspect the wiring to/from the switch -- a short, particularly near the steering head where the wires get flexed under zip ties, would be a cause. So would a short in the relay harness or in the relay itself. I'd also suggest removing the cover over the starter to look for wiring anomolies -- wires shorted against one another or to ground.

 

That should get you started before D.R> steps in.

[Tri]

Thanks...anybody else have any suggestion please feel free to chime in. I will try to trace the wires.

[dirtrider]

Afternoon Tri

 

Not much time on my part here as I only have internet connection for a short time where I'm at now.

 

First off WHAT FUSE is blowing--we can't tell you much unless you tell us what fuse is blowing. (just saying 15 amp tells us nothing)

 

The low current side of the starting circuit doesn't have much of a fuse (4 amp if I remember correctly). If that fuse is blowing (someone might have installed a 15 amp in that cavity). The usual cause of that fuse blowing is a problem in the theft alarm (if your bike has that option). Or a problem in the starter relay. (if this is the fuse then try pushing the starter button with the starter relay removed). If it doesn't pop a fuse then you will have to verify IF the starter relay is the problem (anything past the starter relay is a non player in shorting the start-button side of the starter relay. If the fuse STILL pops even with the starter relay removed then look for a short to ground between the starter button & the starter relay itself.

 

If fuse #4 is blowing (that is the Motronic relay fuse) then look for a failed Motronic relay or a problem in the Motronic (fueling computer) itself.

 

We can probably work you through this BUT we need WAY more info from you on what fuse first.

 

Not sure when I will be back here so hopefully someone will work with you if I don't get back here.

 

 

 

[dirtrider]

The bike turns over, but no spark . Fuses keep blowing

 

Afternoon Tri

 

Added: if it cranks OK then low currant side is OK (ie starter relay, starter button, wiring etc) is OK. No spark, but cranks, sounds like the #4 fuse (15 amp Motronic fuse) is blowing. Not much on that one except Motronic relay & the Motronic itself).

 

Hopefully not the Motronic (fueling computer) as those are expensive.

 

[Tri]

Went back and found that the fuse pops right as I turn the Key to ON position.. Here is a picture of the fuse.

 

[enfoman]

If it is popping like that, my bet right now is with a bad wire insulation hot to ground. Check the wiring up under and around the handlebars and under the dash. As the handlebars move, the wires have been known to pull and.strech because they tightened the hell it of the zip ties in the factory. If.nothing there, at least when tying them back.with slack, you preempt that problem for other wires there. As others have suggested too, check starter for drag, etc.

[dirtrider]

Went back and found that the fuse pops right as I turn the Key to ON position.. Here is a picture of the fuse.

 

 

Afternoon Tri

 

Yep, that's the Motronic fuse that is blowing.

 

My personal next step would be to remove the Motronic relay (engine electronics relay) then see if it STILL blows the fuse.

 

If that makes no difference then remove the fuel pump relay & see if STILL blows the fuse.

 

If one or the other relay removal's changes the fuse blowing then we will have a system to check (ohm) out.

 

I haven't worked on one of those 1200 c's in a long time so I think all that is on that fuse are those two relays (Motronic & fuel pump).

 

If neither of those relay removals change the fuse blowing then we will have to figure out IF anything else is on that fuse (red wire) circuit.

 

Not sure when I will be back here (no internet where I'm camping) so if you don't hear back from me then hopefully someone will take up the quest to help you find your problem.

[Tri]

Good afternoon DirtRider. I believe you are correct. I unplugged the Motronic and the fuse did not pop. When I plugged it back in it popped.

 

Is this brown relay in the pic the Motronic relay?

 

Clymer wiring diagram does not say.

 

[Tri]

OK found this.. Seems like the relay is ok. I unplugged all the relay and put them in one by one and as soon as I push the Motronic relay the fuse popped. So I put in a new relay and it still popped. Can it be the Motronic ECU itself?

 

[dirtrider]

OK found this.. Seems like the relay is ok. I unplugged all the relay and put them in one by one and as soon as I push the Motronic relay the fuse popped. So I put in a new relay and it still popped. Can it be the Motronic ECU itself?

 

Morning Tri

 

Yes, it COULD be a bad Motronic.

 

Most controlled circuits in the Motronic are pull-to-low (pull to ground) type circuits so those (like fuel injectors & coil) shouldn't cause a fuse to blow.

 

The only thing that comes to mind on the 1200C (other than a bad Motronic) is that darn idle control system (idle actuator).

 

Personally I think my next move would be to unplug the idle actuator to see if the fuse blowing goes away.

 

When it comes to diagnosing a bad Motronic (especially on the 1200C)--that is a very difficult at home UNLESS you have a known-good Motronic to swap in as a quick test.

[roger 04 rt]

OK found this.. Seems like the relay is ok. I unplugged all the relay and put them in one by one and as soon as I push the Motronic relay the fuse popped. So I put in a new relay and it still popped. Can it be the Motronic ECU itself?

 

Morning Tri

 

Yes, it COULD be a bad Motronic.

 

Most controlled circuits in the Motronic are pull-to-low (pull to ground) type circuits so those (like fuel injectors & coil) shouldn't cause a fuse to blow.

 

The only thing that comes to mind on the 1200C (other than a bad Motronic) is that darn idle control system (idle actuator).

 

Personally I think my next move would be to unplug the idle actuator to see if the fuse blowing goes away.

 

When it comes to diagnosing a bad Motronic (especially on the 1200C)--that is a very difficult at home UNLESS you have a known-good Motronic to swap in as a quick test.

 

Tri, The BMW Electrical CD shows that there is a model of R1200C without an idle motor. That said, I guess it's likely you have one.

 

My thinking, following the thread and reading the schematics for a while is that Motronic is defective. Although the motor for the idle actuator draws its current through the Motronic (unlike every other output driver, which as DR pointed out doesn't do that), it is highly likely that the design has current limiters in that circuit.

 

One thing you could do is verify that there was no other load on that circuit than the Motronic by removing it and putting a DC ammeter in place of the fuse (note: don't try this with the Motronic installed or you could fry the bike's wires since it's popping the fuse). If zero current with the Motronic out, then the Motronic is the culprit.

 

The other thing you could try is powering the Motronic on the bench and seeing what its current draw is.

 

Lastly, the you could try unplugging all the inputs and outputs to the Motronic and try adding them back one at a time starting with the idle actuator.

 

You don't hear of Motronics dying very often. But on another forum last week, someone fried a ground trace on the Motronic while probing the TPS with wires in pins 1 & 4. He was able to repair that trace.

[Tri]

Thanks I just ordered a Motronic to test.

[Tri]

Update. Just installed my new Motronic and fuse did not blow...I want to thank everything for helping me fix this...You guys have been great thanks!

[biometrics]

Wow! That's great!