electrical??

[JamesW]

I need HEP! Just got back from a trip into northern Nevada yesterday with '04RT not running good at all. Began the ride from Baker City, Oregon to Boise where I dropped off the heads to my '81RT at Big Twin BMW to have new valves installed as she has developed a classic case of the dreaded but not un-common valve recession. Continued on from Boise to Mountain Home then south to Elko, Nevada. Bike ran beautifully in all respects. Next day rode from Elko to Winnamucca, NV then north on US95 toward Oregon boarder with machine running better than ever until we reached McDermitt. We stopped at McDermitt for coffee before beginning the long and lonely run through very desolate country to Jordan Valley, OR and when I say desolate it is an understatement definitely not the place for mechanical problems. Well, wouldn't you know shortly after departing McDermitt the bike began to miss, hesitate under acceleration, and pop loudly into muffler on deceleration. The good news is we made it back to Baker City. Began troubleshooting this morning. Found that machine runs fine on secondary plugs but won't even start with just primaries connected. I have a spark tester which I connected between the primary plugs and the coil sticks and there is spark. Primary plug color looked normal. Why won't machine even start with secondaries disconnected? I should think it should run on only primaries. What am I not understanding? I doubt HAL affect sensor would produce rough running and even stalling at idle but would most likely result in no operation at all. I stopped in Ontario, OR and bought a can of Sea Foam when I gassed up but no help there. Could I have two bad stick coils? Any suggestions would really be appreciated. Oh, didn't miss the ABS for a minute.

[JamesW]

Just connected two external plugs to the primary coil sticks and connected them to a known good (un-painted) ground point and started engine. There is no spark on either primary. Other than two at the same time bad coil sticks the only other thing I can see is a malfunctoned Motronic. What am I missing?

[T__]

James, try actually starting the engine on the secondary’s with the primary’s still hooked to those external spark plugs then see if you have spark.. I don’t have a wire diagram handy here but on some of those dual spark applications there is a 2nd load relief relay on the stick coil circuit (no spark cranking)..

 

If still no spark then check power & ground on the stick coils.. If OK then either bad coils or Motronic (or wiring from stick coils to Motronic)..

 

Actually your problem sounds like possibly bad gasoline so if you get spark then suspect the gasoline..

 

Twisty

 

[JamesW]

Hi Twisty,

I thought bad gas at first but have a fresh tank and same problem. I connected an external plug to each of the stick coils and grounded them and observed no spark on either plug. I then removed the Motronic and measured continuity to the Motronic plug from each stick coil connector so wiring looks OK. I can't see two bad stick coils at the same time so I am thinking Motronic. I wonder if a dealer can test a suspect Motronic by connecting it to a test set outside the motorcycle? My guess is probably not as they are probably plug and play units. My Haynes Manual doesn't show the stick coils and their connections to the Motronic not that it would do much good. Jeez, new valves for the airhead and a Motronic for the oilhead. When it rains .......

[JamesW]

Twisty, what is the purpose of this load relief relay and where is it? Just looked up cost of Motronic...ouch!

[T__]

James, I presumed you checked for spark from the stick coils with the ENGINE RUNNING? If not start there..

 

Do you have both 12 volt POWER & clean GROUND at the stick coil connectors?

 

You might try inserting a 12 volt LED or resisted LED (to work at 12 volts) between the coil trigger circuit from the Motronic & 12 volt power.. The see if that LED flashes as the coil is supposed to trigger.. (get the LED polarity correct )

 

I’m not sure if the dealer can actually test the Motronic’s ability to fire the coil.. It would probably show the Motronic internal triggering but not sure it reads anything on the output side of the coil diver in the Motronic.. (an LED should show you if it is triggering or not)..

 

Twisty

 

[JamesW]

Twisty,

With engine running, just for fun, I closed the gaps on the external plugs to less than .020 and I now get a weak spark. the spark is kind of intermittent and seems to correspond to the rough idle as the motor runs on the secondary plugs. The spark is very weak but is there so there must be a 12 volt trigger from the Motronic. Of course I can't say if it is all of 12 volts or what the trigger pulse looks like. I assume that one stick coil does not affect the operation of the other? Again, I assume the HES are go no go. Am I right in my thinking and if so then it does look like the Motronic but I find it odd that I could have a weak spark as I would expect either a proper spark or no spark at all.

[T__]

James,

 

Have you verified a full 12 volt supply TO the stick coils? (low power to the coils could give you weak spark)

 

Have you verified the ground to the coils? (brown wire)

 

All the Motronic does is momentarily ground the coil primary to make it spark..

 

It’s sounding like you have bad coils—Any way to try your coil(s) in another bike or try a known good coil in your bike?

 

Twisty

 

[realshelby]

Have you considered that you may have had (1) bad stick coil for a while and then the other one just went bad. They can still run somewhat normal with one bad stick coil. I had similar symptoms with my '04 RT. Yes, I had spark with an externally mounted spark plug from the "bad" stick coil. It would not fire under load it seems.

[JamesW]

Terry,

That is an interesting question and a good possibility and I like that scenario a lot better than a bad Motronic.

 

Twisty,

Have verified the ground OK from each stick coil connector. If all the Motronic does is switch a ground to each stick coil then the problem (weak spark) kind of points to the stick coil and to check I really need two stick coils. Hmmmmmmm......

[JamesW]

OK, ate dinner and gave this some thought and I think I put my money on the stick coils being the culprit(s) since they are much more likely to fail than is the Motronic. One thing kind of bothers me and that is why did the primary plugs appear to have normal color if the stick coils had failed? Is it possible that the secondary plugs were doing such a great job that deposits on the primary plugs were just kept to a minimum? Hey, the Haynes Manual electrical diagram shows a common ground point refered to as "Gearbox Earth" anyone know where this point is? Seems there are 4 pins on the Motronic connector that are connected to this point. Could be just a way of denoting frame ground I suppose.

 

My plan is to load bike on trailer and head for Boise and Big Twin and just plug in two new stick coils and see what happens. If that doesn't solve the problem then I will just unload the bike and let them have a great time whilst I massage my bruised and battered wallet. Jeez, those Motronic are spendy.

[Bill_Walker]

OK, ate dinner and gave this some thought and I think I put my money on the stick coils being the culprit(s) since they are much more likely to fail than is the Motronic. One thing kind of bothers me and that is why did the primary plugs appear to have normal color if the stick coils had failed? Is it possible that the secondary plugs were doing such a great job that deposits on the primary plugs were just kept to a minimum? ...Jeez, those Motronic are spendy.

 

My plugs looked fine, too. But changing out the stick coils got it running right. Both sides, '04, 46K miles, lots of riding in hot weather.

 

And BTW, the stick coils aren't cheap, either. About $110-120 EACH.

[JamesW]

Yes Bill, I've been reading through some old posts about this stick coil thing and I guess it is common for the non-firing plugs to not look abnormal. I wish there was a BMW dealer close to me but then I wouldn't get to live in the outback. Probably shouldn't get too concerned about fixing the beast since we will soon be a-shoveling.

[T__]

James, those primary plugs are high in the combustion chamber so as long as the cylinder is working (firing on the secondary’s) the plugs will look just like the combustion chamber..

 

The tiny little spark across the electrode gap has NO effect on keeping the plugs clean,, it’s the heat from combustion that keeps them clean.. You might see a little difference in the electrode area if you look closely but probably not the plug body or lower porcelain..

 

The heat range of a spark plug isn’t based on how hot the spark is it is based on how much combustion heat it carries away to the cyl head.. The heat range hasn’t changed just because it isn’t sparking..

 

Now if they were the lower plugs it might be a little different as the lower part of the combustion chamber gets some oil & combustion residue so those will usually be darker if they aren’t working.. Not so much because they aren’t sparking but more from the flame front not reaching that area so that part of the combustion chamber doesn’t burn all the crud away (that is way those lower plugs were used)

 

 

Twisty

 

[JamesW]

Twisty, thanks for that explanation and reminder about what goes on in the combustion chamber. Wonder what would be the result if one were to simply connect the cables that supply HV to the secondary plugs to the primaries instead. Would the motor run like a normal single spark model? One could maybe save some bucks. I suppose the Motronic might not fire the primaries at the same time as the secondaries in an attempt to get more complete combustion so swapping cables might not be such a great idea, then again....

[T__]

clip~ Wonder what would be the result if one were to simply connect the cables that supply HV to the secondary plugs to the primaries instead. Would the motor run like a normal single spark model? One could maybe save some bucks. I suppose the Motronic might not fire the primaries at the same time as the secondaries in an attempt to get more complete combustion so swapping cables might not be such a great idea, then again....

 

 

James, having never tried that it would just be a guess but I would presume it would run like a single spark engine.. The only thing I can think of in the “why not” category would be spark timing..

I would imagine the Motronic’s built in spark mapping is revised on the twin spark as the flame front would be more conducive to running a little more spark advance..

 

If it were me I would try it to see how it runs.. If you hear any spark knocking maybe try premium fuel.. I would also imagine you will pick up some light throttle/ light load surging..

 

 

Twisty

 

[JamesW]

Twisty, I have been thinking about what a previous poster (Terry) said about the possibility that I lost the first stick coil some time before I lost the second one last week in Nevada. Well, about one year ago I was cruising around Republic, WA when all of a sudden the bike began to experience extreme hesitation and bucking. I couldn't find anything wrong and assumed what I was experiencing was surging caused by the oxygen sensor causing the Motronic to lean and then richen the mixture in an overly aggressive fashion. I bought a Techlusion and switched to Autolite plugs which seemed to generally correct the problem however, I have always had the thought that what I really did was simply gloss over the real problem which I couldn't define at that time.

 

As to connecting the secondary wires to the primary plugs I would have to purchase the single spark cables and they aren't cheap. So, I am going to, for once, play the game and shell out for the stick coils.

 

What is really the pits is that now is really primo riding weather and both beemers are down.

[11101110]

Is there a resistance spec for the primary on the stick coils? Just wondering... If you have some shorted primary (motronic side) windings it would show as a lower resistance. Same for the secondary(spark plug side) but you would probably have to use a spark plug as part of your test lead).

[T__]

11101110, stick coils are problematic to troubleshoot with an ohmmeter..

 

The primary side is around .87 ohms but the secondary side can’t be measured (at least according to BMW)..

 

On the few I have tested it (seems) to be the secondary side that fails..

 

 

Twisty

 

[11101110]

Yeah, .87 ohms is pretty low. Probably below accuracy of most meters owned here. I would think you could stick a spark plug in the sucker and measure off the spark plug. The resistance between the electordes of the spark plug is (should) be way higher than the secondary windings. At least you could get a continuity check.