Author Topic: Starting problem-injector electrical  (Read 5412 times)

Offline KJustin

  • Motobrick Curious
  • Posts: 20
Starting problem-injector electrical
« on: April 15, 2015, 12:05:41 PM »
Hi all, I've posted this problem on the K100 Forum.  Got some good assistance there that helped me diagnose the problem (in part)  but haven't solved the problem, so am seeking additional help.

I'm doing a cafe conversion to my 85 K100RT.  Bike has 87k miles on it.  It was starting and running fine.  Then I took the tank off to paint it.  I put the tank back on and the bike wouldn't start. Befor this, I have never had any sort of problem--electrical or mechanical with the bike.   

I've ruled out fuel issues: starter is working, fuel filter is clear, have fuel at the rail, etc.

The problem is electrical. I have spark. But, I've found that the electrical leads that plug into the fuel injectors are not firing properly.  I hooked up a LED test light to them, bridging the 2 female sockets in the plug.  When I press the starter, I get a blip of light.  Then nothing when I hold the starter, then another blip of light when I release the starter.  It is my understanding that what I should be seeing is a very quickly pulsing light when I do this.  I've also pulled the injectors out of the bike and cranked the starter with the injectors out.  This confirmed what I was seeing with the LED tester--I got one small sput of fuel through the injectors when I released the starter button. 

As I understand it, the way the injector electrical works is that there is supposed to be constant 12v to one side and that the other side switches to ground to create the pulse needed to operate the injector (operating an electromagnet to open and close the needle valve in the injector to squirt the fuel).  I measured for voltage at the injector plug and it seems to say about 24 or 25 volts on one side and nothing on the other side.  I'm not that good with electroinics so maybe I have my multimeter set incorrectly, but it does seem odd that the voltage appears to be double what it should be. 

It was suggested on the K100 Forum that I had a bad or weak ground somewhere that was resulting in the ground at the injector plug not switching on as it is supposed to.  So, I have cleaned all the under tank electrial contacts, main ground, and the plug to the fuel injection unit/computer under the seat. I used deoxit to clean.  Mostly I just opened the various plugs and sprayed it in.  For the main ground, I took that apart, clkeaned all contacts with 220 sand paper, sprayed with deoxit and then put it back together.  Before doing this cleaning, I was getting no light on my LED tester and no spirt of fuel from the injectors when letting off the starter. I'm wondering if I need to do better at cleaning the connections?

I've also tested a few other things, all to no avail: air flow meter seems to be OK, I tried starting with the idle postiion switch unplugged.  I checked that my coils are good by testing resistance between pins 9 and 12 at the injection control unit.  I haven't tested the Hall sensors (but figured this isn't the problem because I have spark--though I'm open to being corrected if I am misunderstanding this).  I haven't checked the water temp sensor.  Should I? 

I'm at a loss about what to do now.  Would greatly appreciate all help and ideas.  Thanks!
 


1985 K100RT converted to cafe racer

Offline dougrs

  • Motobrick Curious
  • Posts: 45
Re: Starting problem-injector electrical
« Reply #1 on: April 15, 2015, 12:56:29 PM »
I can't speak to the electrical issue and measuring volts at the injector as I am just learning the K-bikes. However, there was a recent thread that seems to be similar to your issue: http://www.motobrick.com/index.php/topic,6693.50.html
The culprit there was dirty injectors.
  • MD
  • '89 Yamaha FJ1200, '94 BMW K75

Offline KJustin

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  • Posts: 20
Re: Starting problem-injector electrical
« Reply #2 on: April 15, 2015, 01:24:51 PM »
Always good to check, and I apprecaite all input.  In the other thread it looks like he was getting proper electrial pulse to the injectors, which I'm not getting. 

I'm pretty sure I've ruled out dirty injectors and other malfuncations in the injectors themselves.  Since I have them out of the bike, I took them off the rail.  Filled them with carb cleaner fluid (by attaching a short length of hose, with a bit of compressed air behind it; and, to be sure that I wasn't getting a proper result due to to much pressure, I also did it by blowing by mouth as well) and operated the injector with a 9v battery.  Fluid squirted right out, which indicates that they are clean and the injector mechanisms are operating as well.  Also, I did get one spirt with the injectors on the bike indicating that they are not totally plugged.  And that one spirt is consistent with what I saw on the LED tester  (I also tested that the coils in the injectors were good, and they all measured proper resistance, I don't recall the value right now, but it was correct when I checked it against the reference). 

All other ideas still welcome....
1985 K100RT converted to cafe racer

Offline KJustin

  • Motobrick Curious
  • Posts: 20
Re: Starting problem-injector electrical
« Reply #3 on: April 15, 2015, 03:08:08 PM »
Dougrs, I read that thread a bit more carefully and it gave me a couple of ideas to check on the electrical side.  My apologies for perhaps dismissing your suggestion too hastily. I'll check this evening (hopefully, if I don't get tied up with other things) and report back.

In the interim, still interested in any and all additonal ideas.... 
1985 K100RT converted to cafe racer

Offline dougrs

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  • Posts: 45
Re: Starting problem-injector electrical
« Reply #4 on: April 15, 2015, 03:20:39 PM »
  • MD
  • '89 Yamaha FJ1200, '94 BMW K75

Offline KJustin

  • Motobrick Curious
  • Posts: 20
Re: Starting problem-injector electrical
« Reply #5 on: April 15, 2015, 03:42:13 PM »
Oh yeah, that's a great resource.  I've been using it and it has gotten me pretty far, but not all the way yet (probably in part because I don't have sufficient electrical knowledge to undererstand how to do everyting on there).
1985 K100RT converted to cafe racer

Offline KJustin

  • Motobrick Curious
  • Posts: 20
Re: Starting problem-injector electrical
« Reply #6 on: April 16, 2015, 01:29:58 AM »
Problem solved!!! The ignition control unit plug (under tank, near headstock) had come unseated on one side. I must have knocked it when taking off or reinstalling the tank. Plugged it back in and I'm getting proper firing/pulsing signal using my LED tester at the injector caps now.

Unfortunately I can't put the injectors back in and fire up the bike until I get new injector o rings. They are on the way by mail order; hopefully I'll get them in a day or two.

Yes, I feel a bit foolish, having posted this on two forums, but I'm glad to have fixed the problem. And I learned quite a bit about K electronics, which is a good thing.
1985 K100RT converted to cafe racer

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