What's Wrong????

[Kartman]

Yesterday was the first time in 7 years that my S left me stranded. Here is what it did.

After a couple of hours of riding, it would hiccup when I hit a bump. OK, no wise guys say "then don't hit bumps". Hiccup was a nose dive for a second even when a small road seam was hit. On a smooth surface wide open thru a coupler gears, no problem. After about 15 miles of that I hit a bigger one and she quit completely never to return. I'll skip the goring details of getting it home and go right to what I found, so far.

1. Engine will spin but no sparkies and no fuel pump singing when key is turned to on.
2. Checked all fuses and Motronic relay and fuel pump relay. OK
3. All connectors in front wiring boxes are secure.
4. Carefully checked sidestand switch. OK
5. Checked main cable & connector going into ECU. Just visible under fuel tank with fairings off. Seems tight and no obvious pinched or broken wires.
So, What's wrong??? Could my Motronic ECU have totally crashed.

Being an electronic engineer I naturally suspect the ECU. In my job life I have experienced printed circuit board cracks from vibration that can ultimately develope into an open circuit & functional failure. This has all the symptoms of that kinda nitemare.
Could be a fuel pump failure, but why no spark. Too much coincidence to have a coil & fuel pump failure at same time. Unless the brain (ECU) is not telling them to do their thing.

Any similar experiences or direction would be appreciated before I have to load her up on the trailer down to SCC BMW in Watsonville to do a ECU scan. $$$$

[throttlemeister]

My guess: cable going into the ignition switch, seems to be a week spot.

[gigantic]

Originally posted by throttlemeister
My guess: cable going into the ignition switch, seems to be a week spot.

+1

[JimMoore]

Kill switch, or the wires to the kill switch? Also, maybe the hall effect sensor, but I think you would still have a fuel pump whine with a bad HES.

[Kartman]

Didn't think of ignition switch.

I'll be all over the ignition switch first thing this morning. Should still be sensitive to movement or vibration, hopefully.

Thanks guys.

[JonyRR]

let's start with the simplest thing(s) first. What kind of battery voltage do you have.
What you're looking for, of course, is 13.5VDC at the terminals. Start at the beginning here but for sure the ignition switch wiring bundle being kinked and eventually causing an open there is a good guess. The thin-gauge wire on these things suffere very little stress before pulling an edsel.

[John Lyon]

Originally posted by Kartman
I'll be all over the ignition switch first thing this morning. Should still be sensitive to movement or vibration, hopefully.

With the front wheel back and forth movement over time, sometimes the wires or connections have broken. I "loosened" the wires around my switch some time ago (gave it more slack) to help prevent it.

[Kartman]

Mystery solved. Loose connector on Motronic ECU module.

[Seventies Man]

Maybe a silly question : where is the ECU? Its not the same as the TPS is it? -Martin

[throttlemeister]

It's the metal box underneath the gastank, in front of the battery.

[roger albert]

whereas the tps is the black plastic little box on left the side of your left throttlebody.

[R111S]

Originally posted by Kartman
Mystery solved. Loose connector on Motronic ECU module.

Always be sure to Twist the Throttle between min and max a few times before cranking, after the Motronic Unit has been disconnected from power.