90 K75S no fire on rear cylinder

[Insideoriginal]

Hey all,
 My bike has a chronic misfire/no fire on the rear cylinder. I though it was a clogged injector, so I pulled and cleaned it, put it back, and it started great and rode great for a half hour or so. I parked it for about two/three hours and then started it up and the cylinder was dead again. I’ve done this injector Cleaning four or five times over the course of a few months.

 I parked it and it continued to run with a low idle, just around 800. I thought I’d check for fire, so I pulled the plug wire off the coil and there was no difference in the idle. I put the plug wire back onto the coil and there was no difference in the idle.

 (When I put the wire back on the coil, I noticed it arching from coil to wire, so I’m pretty confident that it’s getting good spark. Also I have brand new plugs and the wires are pretty new (NGKs). Also, I have just complete torn down the entire fuel system, removed washed and dried the gas tank, replaced all lines, replaced in-line and mesh fuel pump filters.)

 Then I pulled the wire off of the injector for the rear cylinder, no change in the idle. I then put the wire back onto the injector and the idle straightened out to about 1050rpm. How would unplugging and plugging in the injector correct the issues?

 Question is, is it the injector or the computer? Or something else altogether. Thanks in advance!!

[The Mighty Gryphon]

What you describe sounds like there is something wrong with the connector for the rear cylinder's injector.  Either the contacts in the connector are corroded and/or making poor contact or there is a bad wire connection to the connector. 

You could start by cleaning the connector contacts on both the connector and the injector with Deoxit.  If that doesn't work, you will need to replace the connector.

The injectors are all wired in parallel, which means that they all share the same output signal from the ECU.  If one of them is not working properly, it has to be in it's connector.  The fact that the cylinder works when you mess with the connector is a major clue to that being the problem.

[Insideoriginal]

Awesome! Thanks for the tip about them being in parallel! I’ll scrub it good and let you know what I find. Thanks again!

[alexg]

Just curious: if the injectors are in parallel, does it mean you can reverse the connectors from say #2 and #3 cylinders with no effect on the engine?

[Insideoriginal]

Just curious: if the injectors are in parallel, does it mean you can reverse the connectors from say #2 and #3 cylinders with no effect on the engine?

I had been thinking/wonder the same thing, but hadn’t had a second to post! I’m guessing that it means that they all fire all the time, right?

[The Mighty Gryphon]

If the wires will reach, there is no reason not to swap connectors from #2 to #3.  And yes, they all fire in unison.

[alexg]

Do they fire every 120 degrees or every 240?

[Roland]

wouldn't the injectors firing at the same time cause the bike to drop in performance ie h;p and torque because its no using all the fuel supplied as well as potentially lower the efficiency with unburnt gas in the intake? This being said, could you get better performance of fuel efficiency by upgrading to a different injection system of carbeurating the bike? thanks

[rbm]

Yes, there is a loss in fuel efficiency by having all injectors fire at once.  You can adapt other ignition systems like Megasquirt and the BMW K Series Engine Management Package from BSK Speedworks.

[Poconoeagle]

Hey all,
 My bike has a chronic misfire/no fire on the rear cylinder. I though it was a clogged injector, so I pulled and cleaned it, put it back, and it started great and rode great for a half hour or so. I parked it for about two/three hours and then started it up and the cylinder was dead again. I’ve done this injector Cleaning four or five times over the course of a few months.

 I parked it and it continued to run with a low idle, just around 800. I thought I’d check for fire, so I pulled the plug wire off the coil and there was no difference in the idle. I put the plug wire back onto the coil and there was no difference in the idle.

 (When I put the wire back on the coil, I noticed it arching from coil to wire, so I’m pretty confident that it’s getting good spark. Also I have brand new plugs and the wires are pretty new (NGKs). Also, I have just complete torn down the entire fuel system, removed washed and dried the gas tank, replaced all lines, replaced in-line and mesh fuel pump filters.)

 Then I pulled the wire off of the injector for the rear cylinder, no change in the idle. I then put the wire back onto the injector and the idle straightened out to about 1050rpm. How would unplugging and plugging in the injector correct the issues?

 Question is, is it the injector or the computer? Or something else altogether. Thanks in advance!!
Wurth. Contact OL.    Best contact cleaner   Evah

[Insideoriginal]

Sorry so long between updates, haven’t had time to deal with it. I cleaned up the connections and tried again. Now I’m really now getting anything from the rear cylinder. I have a little injector tester that I made up with a scrap injector connector and a battery. When I unplug the injector there is no difference in how the engine sounds, but when I plug the tester on to the injector, the engine smooths out for a second, but then gets rough again.

Yo me it looks like the injector might be getting stuck closer, but a full 12 volts of juice is opening it up, but then maybe getting stuck again? Or the cylinder immediately floods and gets rough since it’s just being held open?

There is some low voltage at the injector connector so it’s gettig something, and I have a spare ECU that I swapped and it’s doing the same thing.

I’m thinking the injector itself is bad, anyone agree? These things cost about 10% of what the bike is worth so I’m trying to be conservative about throwing parts at the thing.

Thanks!

[rbm]

Your problem might be related to a plugged prefilter on the injector rather than a gummed up stuck injector.  Honestly, just send all the injectors to Mr. Injector to get serviced.  The cost to get them serviced is worth it and much less than a new set of injectors.

[The Mighty Gryphon]

Another possibility is to watch some YouTube videos on injector cleaning.  If you have to whack it with 12v to get it to open, it's likely that it's getting stuck in the open position or at least closing too slowly to limit the fuel being injected. 

You have the connector and a power source, all you need is a way to get injector cleaner into the injector to do pretty much what a commercial cleaner does.  It will also give you a good idea of what you're dealing with.

[Insideoriginal]

I pulled the injector and soaked it in cleaned overnight. Then, with  it hooked to 12v I hit it with compressed air on both sides as well as some pressurized injector cleaner from spray can. Not sure how much pressure was behind the spray since it came from a can.

Reinstalled and it ran ok for a while but then started with the same issue, rear cylinder not firing. I think I’m going to get a new injector from EME and install to see what happens. They are $50 so not too bad

[K1300S]

Your problem might be related to a plugged prefilter on the injector rather than a gummed up stuck injector.  Honestly, just send all the injectors to Mr. Injector to get serviced.  The cost to get them serviced is worth it and much less than a new set of injectors.

agree.  the services do more than just spray cleaner in the injector.  i use RCEngineering.  sending the injectors off for cleaning, refresh and testing is one of the first things i do when acquiring a old car or MC.

[Insideoriginal]

Pretty good video of Mr Injector himself cleaning injectors.

[bluebossa]

Just fitted a set of 3 injectors to mine - see post below yours..

Transformed what I felt was a misfire and stalling.... mine came with an improved 4 hole pattern... Bike running like a train now...

[Insideoriginal]

I pulled the injectors and found that the little plastic nipple was lodged in the engine. I guess it had been coming loose. Anyhow I replaced the injector and it seems to be running fine now. Thanks to everyone for the help.