K3 - Intermittent Firing on Rear Cylinder

[robertwo]

Ok I've been having a problem with the bike running really rough, so yesterday I finally got around to changing the plugs, oil, filters etc and things are running a bit smoother, but still the rear cylinder is intermittent.

I had the front tyre changed Friday and the guy in the shop was trying to tell me something that he had noticed moving the bike - he was saying it was only running on one cylinder when he started it, but revved it a bit and they both cut in - he thought it might be something to do with the Scottoiler and sucking air..... but I have checked the connection for the Scottoiler as it is connected to the vacum pipe on the rear cylinder and all looks fine. I was planning on removing it for now to see if it helped but it is so tight I could not manage to get it off.

Other things I have noticed/done:
The plugs that I changed were very black when I took them out.
Fuel consumption is about 30-35 mpg
Exhaust outlets both get hot
I have had the coil off and cleaned up the contacts etc
The cylinder seems to cut out when first starting, or when been running at speed then come to stop, say at traffic lights.
The Scottoiler is working fine, so the vacum seems to be intact.
I have tried taking the rear HT Lead off while running and can notice a difference but still seems to run fine on one cylinder
I have tried running the bike on Optimax fuel with Redex added to try and flush the Fuel system through just incase it was anything to do with that
I have had to increase the idle to about 1500 RPM to stop the stalling so often.
Can notice when the rear cylinder cuts out as the idle drops away to about 1000-1100 RPM, and at speed the bike feels lumpy - getting the odd spurt of power.


Does anybody know if there is a way of checking the coils to see if there is a problem? Should there be a certain resistance across them, voltage they produce etc?

Do these bikes have the same functionailty in the Engine Management System as cars do where they can be plugged in to a computer and they return the error codes for whats going on? I'm wondering as it may just be quicker and easier to take it in to a Suzuki Dealer and get them to diagnose the problem, as I know with the car it took them 10 minutes to find the problem while i waited.

Any help would be very welcomed.

[embee]

I'm not particularly familiar with the SV injection system, but from what you say about fuel consumption and black plugs, my guess is that it's running very rich which is often down to coolant and/or air temperature thermistors, more likely to be the coolant one (air temp doesn't have such a big effect on fuelling calibration).

First thing to check is any connectors, take them apart, check/clean, and refit.

Thermistors can fail though it's not that common.

Sometimes if the ECU loses a signal it'll default to some mid value which will keep the engine running in some way ("limp-home mode"), but it's often done so that while it's rich enough to cold start it'll be too rich for fully warm conditions which encourages you to fix it rather than carry on regardless. Could be your situation?? :?

[Apophes]

hi i had very similar thing on me k5 was back coil breaking down under load was fine when tested with multi meter but when under load it was just to say making a spark

i worked out it was the coil by taking back one off and connecting up to front connections and plug bike would not fire

if it is there only 29 squid from your local dealer i found that out after getting 3 off ebay lol

[robertwo]

Embee

You mention about the Coolant temperature sensor being something that could possibly cause an issue, is this something that would only effect one cylinder, or is it more likely that it is effecting both?

I was looking through the service manual and came across a description of this sensor:

ENGINE COOLANT TEMPERATURE SENSOR SIGNAL
When engine coolant temperature is low, injection time (volume) is increased.

I assume that as extra fuel (volume) is being added, this is termed as "Running Rich" and would also maybe explain why the back plug was wet when I changed it.

Anyway, this reminded me that the "Choke" when I start the bike, even on some of the very cold mornings we have had recently, switches off in about a minute. I was wondering how long other peoples stays on for and if this is normal, as the bike will quite often stall, after running very slow and lumpy, within a few seconds of the "Choke" going off. I would have expected this to stay on until at least the temperature displayed on the digital read-out changed from -- to a number.

By any chance you don't happen to know where this sensor is located on the bike?

Apohes, do you have any idea as to how to test the coils.... is there a min/max resistance reading across them, min/max voltage output. i know if I have the lead off when it's running and it gets anywhere close to the frame it arcs across on to the frame or my hand, or a couple of times through the bike and out through the foot-peg which my knee was touching. :?

[Apophes]

if its a nice clean big bugger of a spark your coil is probs ok mine was weak if u use an old spark-plug (working one ) and compare front and back there was a visible difference on mine

the back plug being wet could also be due to it not firing due to back spark

[netsurfer]

When engine coolant temperature is low, injection time (volume) is increased.

I assume that as extra fuel (volume) is being added, this is termed as "Running Rich" and would also maybe explain why the back plug was wet when I changed it.

Right.. the injection time refers to the amount of time the injector is in the open state while under constant pressure. Therefore allowing more fuel through

Pete