Rear Cylinder not Firing

[gt900uk]

Coming home from work tonight the rear cylinder just suddenly stopped. Smells like there is plenty if fuel going in so I guess I need to check out plugs and coils etc. Can I just swap the front coil leads to the rear to see if the rear runs or would the spark not fire at the right time for this to work? Any tips for getting into the coil? Is it an air box off job? It all seems very tight down there and I have left the Haynes manual elsewhere.

[Sid Squid]

Bike, model?

[gt900uk]

Ohh it does tend to help!! Sorry it's an 08 SV650

[jambo]

How have you determined that it's the rear that's cutting out?

Directly swapping the ht leads over from front to rear wouldn't get that cylinder running in the correct timing, as the signals to front and rear coils are timed differently. I'd pull the most accessible plug from each cylinder, ground it on the frame and check if you get a spark when the motor's turning.

Jambo
Sent from my thingie

[gt900uk]

The rear pipe is cold and it runs the same with the rear HT lead off so it appears to be the rear that's out. I Shall check for a spark when I get a chance to have a look.

[jambo]

Is there an FI error message on the dash when it's running?

Jambo
Sent from my thingie

[gt900uk]

Nope nothing. I took the rear plug out and it was a bit black. Cleaned it up
But made no difference. Didnt have time to do anything else tonight. Bike has been running fine with no issues. Shall pick up some new plugs tomorrow and change them then go from there. Last time I had an engine drop a cylinder it was a defective valve seat in my civic. I hope it's nothing to serious.

[gt900uk]

Whats the best method to get access to the coil pack? Do i need to take the tank and airbox off?

[Sid Squid]

Clarification: K8, twin plug, yes? However thus far you've only referred to 'the plug', have you made certain both plugs are connected correctly? If either plug doesn't fire, it's partner won't either.

Make sure of the connections first, both LT and both plug caps. If all seems well, take both plugs from each cylinder and fit them to the other, does the problem move from one cylinder to the other?

[gt900uk]

There is definitely only one plug, just noticed my typo above its on an 07 reg. I am going to buy some new plugs on the way home from work tonight and change them over. I shall see what else i can change over between the two cylinders whilst i am at it. I think i have my multimeter kicking about somewhere so shall try and do some other checks.

[gt900uk]

New plug did nothing, and looks like there is no spark. I checked for voltage on the primary side of the coil and there was 10.5v which increased on cranking the engine. The front cylinder coil exhibited exactly the same behaviour. Just found the service manual online so haven't checked the resistance on the coil (it's dark now) so will have another look tomorrow. To me the coil is starting to look highly likely?

[Messie]

I'm a mechanical numpty, but even I'm pretty certain that on a twin cylinder engine there are two plugs.

You need to look for and find the second plug.

Unless it's a single thingy that you're not telling us about

[gt900uk]

No the front runs ok, just the rear that's gone, so it does have 2 plugs but not in the same cylinder.

I think my next plan could be to connect the front coil leads to the rear coil and see if I get a spark. If not in think I could be pretty sure it's the coil.

[gt900uk]

Ok so have checked the coil resistances and it seems to be in spec. But in comparison though the rear coil only reads 2.7ohm compared to 3.8 on the working front (primary winding). Do you think it could be breaking down further under load causing the issue?

Have also checked continuity of all wires and grounds. Everything seems to connect where it should and I have similar voltage on both coils. I am going to order a coil and fit it, hopefully that will sort the issue.

[jambo]

Can you not unbolt the front coil, move it to the rear and check it that way?

Jambo
Sent from my thingie

[gt900uk]

I removed the rear coil so i could try it attached to the fronts primary inputs. Just need to ground it to the frame somehow. Didnt fancy taking the front off as it looks even tighter to get to than the rear (and that was a pain).

[gt900uk]

Replacement coil and the rear cylinder is now working. Moral even if its within spec it can still be faulty!