2011 XJ6N Cylinder 1 & 4 misfire

[danny_xj6nUK]

Hi all,

New to the forum, just joined as I'm having problems with my XJ6N. Hoping someone with more experience of these bikes may be able to help!
Anyway, problem is a misfire on Cylinders 1&4.
When the bike is cold it runs absolutely perfectly for 3-5 mins, after this the misfire starts. If I swap the coils over the misfire stays at cylinders 1&4. I have equal voltage going to both sets of coils when running. All cylinders have spark, but headers 1&4 are noticeably colder when misfiring.
When it first happened, the bike was really bad, difficult to keep running, however I changed the throttle bodies for another used set and the bike now runs OK, but it still has a slight misfire on 1&4. A mist of easy start into 1 or 4 throttle body seems to bring that cylinder back to life. Seems like it must be fuel related, but I don't think I can be unlucky enough to have 2 sets of TB's with 1&4 blocked. Does anybody know of any other tests I should carry out before I pile even more ££ into this bike? Pretty sure it's either going to be fuel related or ECU.

Thanks in advance for any help!

 

[PRODulcie]

i would recommend checking the injector flow. i’m not sure if that’ll stop it completely, but it would help prove if it’s fuel related or not. also check if the coils are genuine or not, because i’ve found some chinese coil “upgrades” when they get to temp they stutter or stop spark flow. these are just some small issues that could help solve the problem.

 

[danny_xj6nUK]

Thanks for the reply,
Have done a bit more digging on it this weekend, warmed it right up and went looking for the problem. If I run diagnostic program 36 when cold (injector 1&4 test) the injectors work fine and squirt fuel, however once the bike goes above a certain temp, if I run the test again there's no fuel. There's still voltage at the injectors so I'm thinking the ECU isn't sending the signal to open the injectors once it's off choke.

Just to confirm I temporarily bridged the green and black wire from injector 2&3 to the red and black (so all 4 would open from that wire) and the bike ran on all 4 cylinders.

If anyone knows anything else that may be stopping the ecu from opening these injectors let me know but I think I'm looking for a new ECU!

 

[Midori]

Nice troubleshooting!

 

[danny_xj6nUK]

Nice troubleshooting!

Thanks, don’t have a lot to do with fuel injected bikes so took a while to get my head around!
Bike has now been put to the back of the garage while I wait for a reasonable price ecu set to come up. Being in the UK it has an immobiliser so I’ll have to change the complete lockset. Not going to spend big money on it so will be patient for parts.
When the time comes and I get the problem fixed I will update the thread to help out anyone else with the same problem.

 

[danny_xj6nUK]

Just updating this thread as I have fixed the problem and it was indeed the ECU. A cheap unit came up with no ignition etc so I'm now running it with an immobiliser emulator and its back running on 4 cylinders full time. So if anyone has the problem of the bike dropping down to 2 cylinders after 4-5mins id recommend running the diagnostic numbers 36 and 37 once it has dropped to 2 cylinders (you should hear the injectors click 5 times as they open). The injectors are switched to ground via the ECU.

I did try and cut open the old ECU which didnt go that well as the PCB is covered in black silicone (dont know if this is standard as the ECU had previously been opened). When bored I may continue to scrape the pcb on the old ECU just because its junk anyway but I'm pretty out of my depth with that so will likely end up in the bin.

Next job trying to remove the rusty exhaust headers!