Hi again folks,

So I installed the m-unit recently and attempted to start the bike, starter motor works, fuel is being pumped, new battery (up to spec with bike req), MAS getting old, but none of the injectors are spraying fuel nor are any of the spark plugs working. So to diagnosing and I’m just a newbie so take with a grain of salt.

Using crazy frogs diagram, I found that I couldn’t get the led to light up on one of hall sensors, moreover it seems that the previous owner played around with it because the gold screws that hold it in place are stripped. I don’t get signals from the computers to send a pulse.

Second, I found that most of the wires relating to the ignition all have a 12v ground running through them when the bike is off, as if they are acting as an earth wire (- multimeter lead on wire, + on battery). I traced it back to pin 1 on the electronic ignition module (one at front of the bike) however it’s an earth wire.

So, questions. Assuming only one of the sensors is broken wouldn’t the bike still fire on 2 cylinders? Is the negative 12v wires in the bike off position normal? Annnd does anyone have any experiences with similar problems or something to keep an eye on?

EDIT: One last note is if I run the starter then stop, as soon as I stop it will spray the injectors once.

Thanks all

Harry.Dip wrote:I found that most of the wires relating to the ignition all have a 12v ground running through them when the bike is off, as if they are acting as an earth wire (- multimeter lead on wire, + on battery).

Your multimeter test is producing a negative 12V reading likely because you seem to have been creating 12V connections through the multimeter with the leads in reversed polarity. The (–)multimeter lead should be on the battery negative terminal, the (+)lead on the wire being tested. Some wires could read 0V, or close to that, when the ignition is Off; some could read 12V. You should be specific about the colors of the wires being tested and where they are connected.  Photos with clear resolution can be helpful.

You could have component damage or a wiring fire in your future unless you sort out technique and improve understanding—tasks that are often a struggle.

First thing to do is to say what kind of bike/year/2v/16v.

Hall effect sensirs

92KK 84WW Olaf wrote:First thing to do is to say what kind of bike/year/2v/16v.

One of the quirks of this site is that the Information section of member's Profile has a space dedicated to entry of the year and model of a new member's Brick that is being ridden, repaired and/or ruined. The information once entered just languishes there instead of being carried forward to each post the member makes unless the member chooses to put the same information in the Signature section of the Profile, too; otherwise, the reader needs to be curious enough to hunt it down back in the poster's profile.

In this case, Harry's profile indicates his Brick is a 1990 K100RT; however, MaxBMW's fiche indicates the last K100RT models were manufactured in April 1988. Maybe in Australia the model year is calculated at date of first registration. Regardless, that info is close enough for me.

I admit I dont go hunting. Ideally maybe the thing to do is post it in the title since many of us have more than 1 K.

RT does say enough, its 2v or reasonably safe to assume and often year of manufacture and registration are not the same. My K100LT is 92 but as we know it was made no later than late 1991. My 97 K1100LT was made in 1994!! When manufacturers talk of the year they mean the model year, which actually includes from the previous September to the end of the following August!

But for starting if I am right a 2v K initially powers the fuel pump from the start button so in theory the injectors should have fuel [even if they dont open] so I would be wanting to know if my fuel pump is not getting power from pressing the start button. In this case we are told it has power...do we know if it actually pumping fuel...this can happen!

Now one little thing I am aware of, but am not an electronic wizard, is that some features are powered by only one of the two Hall sensors, such as the rev counter....which I think comes from coil 2/3. So when you press the start button...the needle should have some life. If not..Hall sensor?

A thing I found, the connector into the loom as you sit on the bike is on the right of the main spine tube, just aft of the radiator cap. It's vulnerable and has given me issue on one or two Ks and symptom is same as having a dud sensor.

The other thing well worth checking are the two big plugs, to the ICU under the headstock, and the FICU under the seat. Again a bad connection replicates a dud sensor.

Thanks all for the responses. First up it’s a 1990 K100 RT (8v) I put it into the signature for future questions. I’m not sure about manufacturing and what not but it just says 1990 on the vin plate and online registration check.

Next I check for connections mentioned next to the radiator cap and under the seat both are good.

Regarding polarity I understand but that doesn’t fit my situation. I took your advice and did a photoshoot to help convey my situation. So the first photo shows pin 1 on the ignition control unit connector. This pin is the earth wire. As we can see there is 12v running through it because the wire is grounded on the bike already. Now in the second photo I placed the multimeter lead into pin 2, this pin leads to the hall sensor and provides power. Leaving the + lead from the multimeter on the positive from the battery, we can see it says 0, but this is to be expected. But then, if I plug in the connector to the module and measure the same wire but at the hall sensor plugin, it now measured at 11.63. And this isn’t the only pin that does it, every ignition coil pin does it (14, 9, and 10). Now I’m not sure if this is suppose to be happening or not. Moreover, if it isn’t, well if I disconnect pin 1 from the ground, everything returns to normal

92KK 84WW Olaf wrote:Now one little thing I am aware of, but am not an electronic wizard, is that some features are powered by only one of the two Hall sensors, such as the rev counter....which I think comes from coil 2/3. So when you press the start button...the needle should have some life. If not..Hall sensor?

It's 1/4 Olaf (black/blue), but in truth the rev counter couldn't care less which coil it gets its signal from.

Harry.Dip wrote: First up it’s a 1990 K100 RT (8v) I put it into the signature for future questions. I’m not sure about manufacturing and what not but it just says 1990 on the vin plate and online registration check.

Let's start with clarity here. The most important information you have provided so far was in your Introduction post. It was
I’m a naive yet motivated individual who knows nothing about mechanics . . .

Let's build from that statement. You don't seem to be acting naive; you seem to be acting like somebody who knows what's going on. In that category, you're way ahead of me. 

There is no K100RT(8V); there is a 1990 K100RS(8V). Your Brick isn't one of them. The photo of the Brick nested in a tangle of wire in your Introduction post is that of a 2 valve Brick with a monolever rear drive system. Put the last seven digits of its serial number in the serial number search box of this VIN checker and see if that helps us.


You need to educate yourself not only about which Brick you've got but also about how it works and how its components and systems are tested. With wiring in a mess like that, you're definitely in a pickle. Your native genius alone might not be enough to overcome the challenge. I guess that's why you're here but additional resources are available.
 
There are three resources you possibly could be willing to study for guidance—The LE Jetronic Training Manual; Diagnosing and Testing Instructions for K Models; LE Jetronic Diagnosis and Test Equipment Manual. Their download links are available at this page. The D and T test manuals are based on BMW's proprietary tester so adaption of instructions to a multimeter like yours is limited, especially with your seeming lack of experience.

Good luck with your project.

SOLUTION: Ignition hall effect sensor needed replacing.

Regarding the -12v happens when the circuit is not complete. I found that other components such as the temp sensor relay will have wires that turn into a -12v when the ground isn't connected however the amps aren't high enough to damage anything