Starting Problems

[Zfoster8]

Hey all,

I mentioned a bit in my intro post but figured i would dig into more detail about my problems with not being able to use my starter on my 87 K75S.

Picked the bike up about two weeks ago "not running". Previous owner said he thinks it was the starter relay, so thats where i started looking. Bike starts and runs very well with rolling bump start.

Basically, when i press my ignition button i can hear the fuel pumps running and nothing else. Starter does not engage, lights do not turn off, nothing else happens.

Things i have done and checked so far:
Replaced starter relay (more details in a bit)
Verified starter motor works (hot wire from positive battery terminal to starter, motor spins over and starts the bike)
Checked load cell (swapped with horn, both work fine)
Ripped apart handlebar controls, cleaned connections and checked working order, reassembled
Battery is good, healthy, and fully charged.

Starter relay: the one in the bike is beat, someone obviously already tried to tinker with it. The case was a bit busted. Replaced it with a new OEM bosch unit. After installing, realized previous owner had swapped the power and starter wires. Changed them to the right terminals, gave it a couple good whacks for good measure, no change.

For kicks i took apart the old one, and the terminals were not fused together, it actually looked pretty good inside.

I guess my next steps are to start checking everything else, but does anyone have any recommendations on where to start?

A quick note, the previous owner (or whomever) has done a lot of "custom wiring" to accommodate LED lighting i am guessing, and the wiring harness is pretty raggedy and hard to trace. This obviously makes it a bit more difficult.

Thanks in advance!

[johnny]

greetings...

if you are serious... you better start poasting up photos here so we can see what you see...

and in this thread list everything that you think was done to the moto before you gotts it... and list everything that has been done after you gotts it... in chronological order of course...

be specific... no willy nilly... cause we dont deal in hearsay opinion mind reading hypotheticals here at motobrick.com... this is a fact based community based in reality...

j o

[daveson]

When you turn the key to on,  you should hear (and feel)  a click from the starter relay.

[Zfoster8]

Daveson - There is an audible click when i turn the key on.

Johnny - Pictures incoming.

I have been able to trace almost all of the wiring and it does look like nearly all of the modified wiring is for lights and some accessories that were never finished being installed - There is an oil pressure gauge, voltage gauge, two toggle switches and a couple little notification lights. None of them work except the one indicating whether the turn signal is on.

I have done almost nothing to this bike so far aside from clean it up a bit and put in the new relay.

Added a "nude" of the old starter relay for your viewing pleasure


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20191102_163041.jpg (62.77 kB . 768x576 - viewed 688 times)

[johnny]

greetings...

battery is good healthy fully charged...

whats your battery voltage... getts it on a tender now...

j o

[Zfoster8]

Johnny - it is currently plugged into a tender and fully charged - reading 13.65 volts on the multimeter

[Zfoster8]

Yeah brushes and a cleaning are probably in my starter's near future. Certainly can't hurt anything anyway.

[volador]

If you pull the clutch lever in when starting anything?

Two interlocks interact: It should start if it is in neutral; or if the clutch lever is pulled if in gear. The clutch switch mounted on the clutch lever perch.
There is a transmission gear position indicator switch on the transmission rear.

So, if in gear pulling the clutch should allow it to crank. If not, the clutch switch is suspect.

If the neutral light fails to come on the TGPI switch seems faulty. If both get bad it won't start.

The "load shed relay" which has the headlight and some other stuff connected grounds to the hot brush of the starter. If the starter is not energized this provides a path to ground for the relay coil, thus providing current to the headlight, etc.

However, when the starter button is depressed 12v+ is applied to the hot brush. And the load shed relay coil now has 12v+ applied to both ends of the coil - thus no ground. So the relay turns the headlight and stuff off until the starter button is released.

https://forums.bmwmoa.org/showthread.php?94841-1990-K75RT-Electrical-problem

Starter motor cleaning / rebuild tutorial

Main harness connectors under the tank
Choke switch: Violet/White and Brown

Clutch switch: Green/Black and Black/Green

[Zfoster8]

Pulling in clutch makes no difference. In neutral, ignition switch triggers fuel pump. In gear with clutch does same. Lights never even so much as dim when ignition is pressed, which i guess means no current is making it to the starter at all. Gear position indicator works, it shows every gear i cycle through.

In gear with clutch not pulled in does nothing at all, which confirms the switch works i suppose. Just went and checked.

[Laitch]

I guess my next steps are to start checking everything else, but does anyone have any recommendations on where to start?

Consider checking the wiring junction marked by the magenta box on the left side of the attached diagram and the condition of the wiring marked by the magenta arrows in the diagram at the load shed relay.

Load shed:starter circuit.png (44.75 kB . 768x218 - viewed 682 times)

[volador]

Consider checking the wiring junction marked by the magenta box on the left side of the attached diagram and the condition of the wiring marked by the magenta arrows in the diagram at the load shed relay.

Load shed:starter circuit.png (44.75 kB . 768x218 - viewed 682 times)

Magenta such a pretty color. Where is my magnifying glass?

When you turn the key to on,  you should hear (and feel)  a click from the starter relay.

You hear a click from the LSR

[volador]

Is it possible there is security switch?

Check your ground points 1- frame ground wire connection on the left side of the center frame tube under the gas tank
2- left foot peg plate area

Check for +12v power on the blk/grn wire at the starter button

The 9 pin plug for the right hand combo switch terminal #6(black/green) of that connector is the feed to the starter switch. the output of the starter switch (that goes to the starter relay coil connection) is terminal #1(black/yellow wire)

Next step would be to check starter relay coil +12v and ground, +12v wire is black/yellow and ground side is brown/blue.

[daveson]

True, turning the key to on closes the LSR.  I should have said pressing the start button,  but then they both click. A better way would be to check for power to the starter motor positive,  when you are sure the earth to the starter is good. If you have power at the starter with the start button pushed, and it doesn't turn, dismantle the starter,  you probably have worn brushes. I just recently fixed this problem on my bike. While it's open test it and clean it.

But the lights don't cut out so the symptoms match what the PO told you, a failure at the starter relay.  So check for constant power to 30, power to 86 with the start button pushed and earth to 85.

Does the starter relay click with the start button pushed?

[The Mighty Gryphon]

First, what is the voltage on the battery with the tender disconnected?  Turn on the lights for a few seconds before checking the voltage to remove the surface charge from the battery plates so you get a more accurate reading.

The condition of the starter brushes is critical.  If I had starting issues with an unfamiliar brick a starter service would be the first thing on my agenda.  You say the lights don't dim, which tells me the LSR isn't being pulled in, and that depends on current flow through the brushes, commutator, and the starter motor windings. 

[daveson]

A click was heard with the key turned to on (LSR) though we don't know if it was felt. If the starter relay isn't providing power to the starter, the lights won't cut out.  There is a big question mark over the starter relay. I'm assuming the battery is good, that's another big question mark.

If, with the LSR removed, a click isn't heard or felt from the starter relay with a quick jab of the start button, that's a problem.

[Laitch]

Magenta such a pretty color. Where is my magnifying glass?

Don't concern yourself with finding it. The response wasn't meant for you.

[Zfoster8]

So here are the readings i have gathered so far. These are with no battery tender, and i had the headlight on for a minute to drain residual pixies from the lines.

I will refer to the terminals of the starter relay by the listed numbers on the unit. Power in is 30,  wire to starter motor is 87, wire to ignition module (?) is 85, two wires to other things are 86.

No load, key off
Battery - 12.9 volts
terminal 30 - 12.85
terminal 86 - 0
terminal 85 - 0
terminal 87 - 0

Key on, load shed clicked, starter relay did not click
battery - 12.32
30 - 12.26
86 - 1.0
85 - 1.05
87 - 0

ignition button pressed - lights still on, don't dim and fuel pumps running
30 - 12.16
86 - 10.0
85 - 9.85
87 - 0

I guess this determines that power is coming through everywhere it needs to, but the starter relay is not closing and transferring that power to the motor.

[The Mighty Gryphon]

Under the tank near the front is the ignition control module.  Check to make sure the terminals in the connector are clean.  Give them a shot of Deoxit and reconnect the connector to make very sure it's not loose. 

Your readings make it look to me like there is a bad ground connection on the red/brown wire that goes from the starter relay to the ignition control module.  It could be a broken wire, loose connection or a problem in the module. 

A quick test to see if the problem is in the red/brown would be to run a wire from that terminal on the starter relay to ground.  Then push the start button.  If I'm right about the red/brown wire, the starter motor will spin.

[Zfoster8]

Gryphon -

The ground wire to the brown/red wire terminal worked, and i am so giddy excited. This is the first time the motor has spun over from the ignition switch the whole time i have had the bike.

Now i need to pull the tank off somehow and get a good look at that ignition module.

[The Mighty Gryphon]

Let's hope the problem is a loose connector.  You might also want to check the continuity through the red/brown wire between the terminal on the starter relay and pin 11 on the ignition module connector just to make sure the wire is good.

[The Mighty Gryphon]

Terminal #15 on the ignition module looks like the rest of the ground path for the starter relay.  It looks like it connects to the frame under the tank.  It is a good idea to make sure that wire is not broken and makes a good connection to the frame.  With the tank off, it's a really good time to clean up the ground terminals and their connection to the frame.  Make sure there is no rust on the frame and that the wire terminals are nice and clean and shiny.

[Zfoster8]

Leave one problem, find another.

With the 85 terminal grounded, it seems i welded the connections closed on the relay and the starter motor kept running after the bike fired up. Had to disconnect the battery to get it to stop. Battery lead kept arcing to the terminal until i gave the relay a couple whacks.

The connector to the ignition module looks pretty good aside from being very dusty. The rubber boot was not on, and there was a good amount of gunk in there. I gave it a blow out and hit it with a cotton swab but I don't have any deoxit on hand, i will have to pick some up. after the brief cleanup, the problem is persisting, still not starting and now i am worried i might need yet another starter relay if it keeps welding itself closed.

As a layman who has never actually used a multimeter before this... what is the best way to check continuity on a single wire?

i will clean up that ground point on the frame, i did notice the brown ground wire coming out of the ignition module has some tape on it which makes me think it broke and was taped together. I will investigate this right now.

[Zfoster8]

Cleaned up the ground spot, it was pretty grimey. Ground wire is good, tape was just some kind of identification on it. Didn't fix it unfortunately.

[daveson]

Set your multimeter to Ohms to check continuity of the brown/red wire, with the wire unplugged at both ends. As soon as you have finished the test,  get straight out of Ohms.

The starter relay jamming is a classic hallmark of a poor battery, maybe get it tested.

[Laitch]

As a layman who has never actually used a multimeter before this... what is the best way to check continuity on a single wire?

Does that mean you've hypothetically used a multimeter? :-)

A Google or DuckDuckGo search will reveal plenty of videos explaining the process. Probes or clips are placed at either end of a wire. How continuity is expressed depends upon the multimeter's features—beeps, digit values, symbols, snippets of death metal, etc.. Spend fifteen to thirty dollars, follow the instructions.