Help please I have a situation:

cold engine runs well, but when get hot it begin to drang drang - and rpms goes up and down a bit:

I checked coils, changed water temp sensor, changed FI, changed spark plugs and nothing. ..

Finally started to test injector plugs (connectors) and found that hot engine runs the best way with cylinder 2 and 3 injectors unplugged. I cant believe that bike runs relatively smooth (on idle of course) only with injectors 1 and 4.

What is it? What to check?

Drang drang........hmm......this is a tricky one.




I would guess a faulty hall sensor, have you checked that you got a steady pulse
from the rearmost coil....when the engine is at operating temp.

The injection module is working the injectors twice per cycle (once per revolution) and all injectors open and close at the same time (IIRC). Further cyl 1 and 4 are 'linked' over the first injection coil and cyl 2 and 3 over the second. There is something wrong when you unplug two injectors and the bike runs better (but you already knew that). It sounds as if the bike is badly adjusted mechanically or through sensor issues.

Do you know the history of the bike. What did you do or have happen that is is suddenly running so bad?

I would go back to zero. Check signal wires and then start the bike adjustment fresh. Check valve clearance and fuel pressure, check working of injectors and if all spark plugs work, check the tb rack in moving freely, if right than check timing, check no air leaks in the rubber bits, which includes making sure the rubber elbow between plenum and air filter box is properly fitted (air leakes sometimes can sound like a bonking noise), then synchronize the bike.

Thanks Rene, everything was good for years, maybe 30 - 40 tkm. I adjusted valves few months ago. It started with strange noise from fuel pump which continued and bike started to run erraticaly on idle. I changed pump, changed water temp sensor, changed hall sensor, FI computer, I have a new pair of coils ready to change.
Could it be box under the tank, near the head of frame?

nino wrote:found that hot engine runs the best way with cylinder 2 and 3 injectors unplugged.

ReneZ wrote:cyl 1 and 4 are 'linked' over the first injection coil and cyl 2 and 3 over the second.
ReneZ, I believe your are talking about the ignition coils because the 4 injector coils are linked together.
             

Nino, Do you see a pattern there?
I would say a bad coil or yes the ignition module in front of the fame.
A quick test for the coils would be to reverse them. (You have to physically switch them as I believe the wires will not be long enough)
After the switching, If the engine runs better with cylinder 1 and 4 unplugged, you have a problem with a coil. Otherwise, I would look at the ignition module or at the Hall sensors.

Thanks Bert, I changed the hall sensor and nothing happened. On cold engine everything sound very well, even hot on higher revs sound normal except high consumption. Could it be dirty contact on water temp sensor? I found that contact full of oil and try to clean but think isnt clean still. Is it possible that sensor because of dirty contact sends wrong signal to engine management?

Two cylinders together, as in1/4 or 2/3 points to coil, condenser or anything on the circuit because each coil serves two cylinders.

Swap coils, its easy and if the problem moves to the other two cylinders 1/4 then your coil is problem. If the problem disappears you can figure it was a bad connection. If it remains and doesn't move to 1/4 suspect the wiring and/or connections to the 2/3 coil but also make sure the connections and grounds are good.

The ECU unit at the front of the frame may need to have the contacts cleaned off. But go for coils first because they do tend to fail with age and can damage the ECU at the front of the frame if left in poor condition.

Don't read too much into unplugging the injectors as these bikes will often idle with injectors disconnected because the manifold vacuum will drag enough fuel through the open pintle valve to let them idle. Not all the injectors but 1 or 2.
You say the temperature sensor was full of oil, which sensor did you remove, if you removed the sensor on the oil/water pump you may have removed the oil light switch.

if you removed the sensor on the oil/water pump you may have removed the oil light switch.


No, it was a water temp sensor, but somehow the plug under the radiator was oily

Gee that is a bit odd maybe the cam chain cover was leaking a bit. It's the only place I can think it could come from there.

Thanks Rick, this afternon I ll swap coils. I have one spare pair with me. I hope its not ECU because spare was from swiss bike with limiter on 6500 rpm