No Injection/Funky Voltage

[Carter]

Howdy. First time bike owner here. Young gun trying to learn motorcycles. I bought a non running 1984 k100rt and have been running through the electrical system to get it to start. I have cleaned the injectors and used jumpers to test for functionality, it checks out. I put them back on the rail and leave it unconnected from the engine so I can make sure they spray. I have tested for 12V on the injector connecters and that’s where it’s shaky. With the airflow sensor and idle plugged in and the EFI disconnected, I get 12V at the connecters with starter active. With the EFI plugged in I get around 2V.  Could this be a grounding issue with the EFI? Been reading everything I can get my hands on and still cannot seem to solve it. Thanks in advance!

[The Mighty Gryphon]

Welcome!  Do you have a wiring diagram for your bike?  Troubleshooting will require following wire colors and pins on the engine control unit (ECU) and the ignition control unit (ICU). 

The basic operation of the injectors is that they get 12v applied all the time the ignition is on, and are opened by a ground signal from the ECU that is coordinated with the ignition signal that comes from the Hall Sensors on the front of the engine by way of the ICU. 

Where are you reading this 2 volts?  When the engine is cranking the ground is being pulsed on and off by the ECU, so it may be that you are reading a pulse on a meter set for DC voltage.  That can give you a faulty reading. 

[Carter]

Thanks for the quick response! So here’s on back. I was reading the 2V at the injector connections. I’ll have to check to see if my meter is reading DC voltage. With the EFI disconnected, the injectors would still get 12V just not grounded correct?

[The Mighty Gryphon]

Someone else should be around here in a bit to help you out.  I am tied up with a bunch of Spring jobs right now, and won't be back here until this evening.  I'll take a look at my wiring diagrams at that time.

[rbm]

The injectors are operated through transistors in the ECU that periodically connect the Yellow/Grey wires on each injector to ground.  The ON time is quite short so DCV readings with the engine cranking will be low (i.e. average voltage of a pulsed square wave is very low).

Where are you taking the voltage reading when the ECU is plugged in? 

Is the engine stationary or turning over at the time? 

Have you listened to each injector using a screwdriver like a stethoscope to listen for clicking sounds while the engine is turning over?

Have you verified the operation of the Hall effect Sensor assembly (the ECU will not fire the injectors unless the ICU tells it what the engine speed is and the ICU won't know the engine speed if the HES is faulty)?

[Carter]

Hey Robert. I was taking the voltage at the injector connectors at the rail. These readings were taken while the engine was cranking. I have tried the screwdriver trick and didn’t hear anything. If I am getting spark, wouldn’t the HES be intact? Appreciate the responses!

[Laitch]

Have you downloaded read the LE Jetronic testing and explanatory manuals on this site, Carter, or Vogel's troubleshooting guide here?

[frankenduck]

Have you downloaded read the LE Jetronic testing and explanatory manuals on this site, Carter, or Vogel's troubleshooting guide here?

Here's a PDF of it:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/k100tshoot/K100.Troubleshoot.Start.2018.pdf

[Carter]

Yes! I have been familiarizing myself with that document. That’s what I used for my initial testing. I will run back through it once I get off work to double check my work. I will let you all know what I find! Thanks for the quick responses. Quick question for anyone who may know, what is the minimum components that are needed for the engine to fire? Can I unplug the airflow sensor? Throttle idle? Or anything like that and it still start?

[Carter]

Ok after a little more testing, I have double checked the flow chart for LE systems. I have gotten to “12V at pin #1,9,12” to which I have no voltage except for .10 on pin #1. This points to “renew as necessary”. Having done that test on the female side of the plug, how does that point to the ECU needing a renewal since the ECU is disconnected to do the test? Or would something else cause that? The ECU is the silver box under the seat correct? Appreciate the help.

[Laitch]

Here's a PDF of it:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/k100tshoot/K100.Troubleshoot.Start.2018.pdf

Although that's the most widespread reference, I was referring to these two. Carter wasn't referring to FICU and ICU pin numbers in his testing so it was difficult for me to know exactly what he was testing and what values he was using for reference to draw his conclusions. The situation is starting to be clarified.

[Laitch]

The ECU is the silver box under the seat correct?

That is the Fuel Injection Control Unit (FICU). The Ignition Control Unit (ICU) is nested within the frame under the tank. Using those specific abbreviations helps to clarify what you are testing.

[Carter]

Yes! Ok now we are on the same page. For some reason that document I was looking at referred to the ECU, which I assumed was the FICU, same thing. Photo below is what I was referencing.

[Laitch]

Yes! Ok now we are on the same page. For some reason that document I was looking at referred to the ECU, which I assumed was the FICU, same thing. Photo below is what I was referencing.

Familiarity can lead to the assumption that everyone knows terms being used. The best communication arises from specific reference. Circle all the yes and no flow chart directions you've completed, and indicate where you are now. Be sure to review the testing manual at the link I previously posted, too.

[Carter]

Here is the picture of where I am at now. Tested at female end of connecter. Wondering if it’s the FICU that they are suggesting to be replaced, since the testing was done before the signal to the FICU. Sorry for all this confusion. I am confused and learning it all from the ground up.

[Laitch]

Whatever your background in electronics testing is, Carter, it seems that you should review how the whole system works before you interpret your test results. Have you already done that? If not, I recommend your reading the Level 2 LE Jetronic Manual at the first link I provided. After that, I recommend abandoning that particular flow chart and returng to the troubleshooting guide you’re using now to review ignition control unit testing at p.13 and the fuel injection control unit testing at p.23.

Testing is usually done with wiring harness in place on a Brick that developed problems while being ridden. Where is your Brick in comparison to that situation?

[Carter]

I have zero electrical testing experience. I have about 72 hours into this bike learning how to do it all. this bike was bought together, but without the fairing. A mouse had eaten the wiring and nested in the air box. I will review the information that you have presented. Thanks

[Laitch]

You need a wiring diagram for your year and model of Brick. You should learn how to determine continuity with your multimeter. There are color-coded wiring diagrams of both electronic control units in the Testing for K Models manual. Wiring diagrams to download can be found here on this site and at this resource found in its Third Party section for the K100.

I use three references for repair Chilton, Haynes, the K100/K75 2V BMW service manual downloadable at this forum. One of those references is likely to have an explanation for mechanical procedures that can be understood when the others aren't, but none of them delve deeply into the electronics like the two links I provided to you. Luckily, there are several members here capable of helping you along with that side of things. Which type of multimeter are you using, analog or digital?

This is a large undertaking for somebody at your stage of experience. Be patient. Review information in your references frequently. Verify what you encounter around the Internet. Questions are welcome here.

[frankenduck]

What's the extent of mouse eaten wiring and in what area of the bike?  Got of pics?

[rbm]

Mouse?  That is an important detail to leave out.  Your non-starter would certainly behave strangely if the wiring loom was compromised.You would benefit by extracting the entire wiring harness and doing an inspection.  Or buy a new (used) one.

[daveson]

I might be a bit late to this thread but here she goes.

The multimeter is one of the best tools for diagnosing, but if you're new to bike's and cars, it's easy to use wrong and get wrong results.

The injectors are simple, they just need power and a pulsing earth to run properly. Since the injectors are working, they're probably not getting at least one of those.

A much more simple tool to use is a test light, in this case it needs to be a computer safe 12 Volt LED test light.

Remove a plug from an injector. With the test light clipped to battery negative, the light should glow with the probe touching one of the plugs terminals when the starter button is pressed, that will be the positive terminal. The light will remain off at the other terminal because that would be negative to negative.

Now clip the test light to battery positive. With the probe on the negative terminal and the start button pressed, the light should pulse on and off.

This is a simple test to see if the injectors are getting earth and power. It would be good to unplug the tank connection so that fuel doesn't get pumped into the other cylinders while you do these tests.

[daveson]

In this photo the positive is on the right.


IMG_20230521_134535.jpg (19.63 kB . 432x576 - viewed 561 times)

[daveson]

I'm trying to attach a video of the pulsing earth while cranking, but not having much luck.


IMG_20230521_164328.jpg (33.75 kB . 432x576 - viewed 531 times)

[Laitch]

Here's an example using an automobile system but the same principles apply. A test light is used in one of the trials.

[daveson]

Here's the video that previously I was only able to post as a photo.


https://youtube.com/shorts/Hqttqo-y0xg?si=URsEiBFEtqCY8r1Y