Stator Causing Stalling?

[MadDuck]

The bike has been at the dealer for a couple months now with the problem of stalling at idle once the engine has warmed up. If the engine is cold it will start & run with no problem. Once warm it stalls at idle but will restart & run if the throttle is held open off idle. No warning lights are on and no fault codes have been set.

At this point the dealer has called a bad stator and is waiting for parts.

Here's my question. How can this be a bad stator?

If the stator is bad then there should be no charging to the battery and there should be a charging system warning light. No warning light is on when this occurs and the light does work as it is on when the ignition is switched on just before starting the bike.

The battery is strong enough to restart the engine when it stalls. Therefore, according to what I've read, it should also have enough power to keep the system voltage above the threshold where the ECU doesn't have enough power to run.

I can understand that a stator can short when hot and stop charging. This should be measurable by having a volt meter hooked up and watching the charging rate at idle. Again, from what I understand, if the charging drops below threshold the battery should take over and keep things going until it's available voltage drops below threshold. At that point there shouldn't be enough voltage/amperage in the battery to where the engine can be restarted yet it does start and run as long as you don't let it idle.

Is my thinking / understanding of all of this correct?

[Howie]

If one of the three phases is out or under performing you could have a voltage issue at idle, so it is possible.  What tests did the dealer do to determine the stator is at fault? 

[Speeddog]

I've not encountered many bad stators, but from memory, if they have a winding shorted to the armature (ground) , they can't keep the battery charged up.

They can have a short *in* the winding, which may cause an under-performing condition, but.....

We need a true sparky in here.... Paging suzyj to the white courtesy phone....

+1 on what tests, and what results.

[MadDuck]

So far as I know they are going after the stator because they can't find anything else wrong.  In one way I'm fine with that but I also think that this fault should be able to be proved with quantifiable test readings.  If that doesn't fix it then you can bet there will be some discussion as to who pays what for what.

[Howie]

Exactly.  Measure resistance on each winding, continuity between windings and ground.   Then test output on each phase.  Passes?  Now add some vibration to the situation.  Sometimes diagnosis by guess, particularly if the situation is intermittent can be a good route, but not when the guess is so expensive and unlikely.  Any chance the bike is under warranty?

[suzyj]

Hmmm...

Have they checked the powerband?

Seriously though, your logic is correct. Ain't nothing wrong with your stator, and even if there was, it would cause charging trouble (and hence no start) rather than idle problems. Even if the stator is completely shorted together, it can't cause the voltage to drop after the rectifier/regulator, because the diodes in the rectifier part ensure current only ever flows out of the stator.

It's a good idea to check connections between battery and ecu, battery and engine case, etc., as if these get a little loose you could have trouble idling when hot. Open connectors, give the contacts a brief spray with contact cleaner, then close again. Also check the ground under the ecu.

Fuel pump wiring on modern ducs is also a common source of grief.

[Speeddog]

Which bike is this....BTW.....

[brad black]

What he said.

Aprilias will do this, backfire and stall, restart ok.  Charging system faulty, their brown connector all melted usually.  Seems to be the late models with the Siemens ecu (2004 onwards magnesium motor) from memory.  No idea why, but it is a common cause/effect.

Never seen a ducati do it.

[scaramanga]

Exactly.  Measure resistance on each winding, continuity between windings and ground.   Then test output on each phase.  Passes?  Now add some vibration to the situation.  Sometimes diagnosis by guess, particularly if the situation is intermittent can be a good route, but not when the guess is so expensive and unlikely.  Any chance the bike is under warranty?

This is a good test for an open(broken wire)  "phase winding" but will not tell you if the winding insulation is breaking down causing a voltage leak to ground. When using a multimeter you're only applying less than 9volts to measure resistance , not enough to measure bad insulation. For this you need to perform a hi-pot test (high potential) between phase and ground. I doubt you have this instrument or even the dealer.  What this does is apply a higher voltage than normally seen by the winding to see if the insulation breaks down.
The measured value is resistance, high resistance= good, low resistance = bad , at test voltage.

[J5]

i doubt it is a stator problem

this can easily be tested when you start to have the issue

disconnect the stator and see if the problem goes away

also disconnect the reg/rect

I would be looking more at ignition side of things

coils , ignition trigger , spark plugs , tps

it will be heat related imho

of course it could be something as simple as valve clearances

[Howie]

What he said.

Aprilias will do this, backfire and stall, restart ok.  Charging system faulty, their brown connector all melted usually.  Seems to be the late models with the Siemens ecu (2004 onwards magnesium motor) from memory.  No idea why, but it is a common cause/effect.

Never seen a ducati do it.

Seen it on cars too.  A not too good battery (but good enough to start) can cause this too.  If voltage drops too low at low engine speed it can cause both computer and fuel delivery problems.  AC ripple, which can be caused by a bad stator, but more likely a bad diode can cause computers to misbehave too, though less likely on newer designs.  AC ripple is an easy test.  AC meter on the lowest scale.  Positive to battery positive.  Negative to ground.  Run vehicle.  You should see less than.1 volt AC.  Or you can use an oscilloscope and look at the sine waves.

This is a good test for an open(broken wire)  "phase winding" but will not tell you if the winding insulation is breaking down causing a voltage leak to ground. When using a multimeter you're only applying less than 9volts to measure resistance , not enough to measure bad insulation. For this you need to perform a hi-pot test (high potential) between phase and ground. I doubt you have this instrument or even the dealer.  What this does is apply a higher voltage than normally seen by the winding to see if the insulation breaks down.
The measured value is resistance, high resistance= good, low resistance = bad , at test voltage.

Yep an ohmmeter is not too good for bad insulation unless it is really bad.  your hi pot is important in pinpointing a bad stator, but not for determining a charging system is malfunctioning.  Back in the old days we used an AC test light, household voltage, with an incandescent bulb  Bulb lights, stator bad.

A diagnosis I am still proud of today.  19?? Chrysler Vision no start.  Cranked well.  Everything was tried, including a new main relay and computer.  Problem?  Bad segment in starter.  Every time a brush past the bad segment the computer would drop out.  Change starter, problem solved.

Back on track, though I do think it is possible MacDuck's bike could have a bad stator, I highly doubt it.  

[scaramanga]

Yep an ohmmeter is not too good for bad insulation unless it is really bad.  your hi pot is important in pinpointing a bad stator, but not for determining a charging system is malfunctioning.

correct, this was an offline test to determine if the stator insulation is problematic.
If the charging system is working properly you should be able to disconnect the battery ,after starting ,and the bike should run normally. If it stalls further investigate charging system. If it runs , battery disconnected, then wiggle connectors and wires with the hope of a stall.

[Speeddog]

Until we know what bike it is, I strongly recommend *not* disconnecting the battery while it's running.

[kokis]

All injected Ducati will stop at battery disconnect.

[Howie]

correct, this was an offline test to determine if the stator insulation is problematic.
If the charging system is working properly you should be able to disconnect the battery ,after starting ,and the bike should run normally. If it stalls further investigate charging system. If it runs , battery disconnected, then wiggle connectors and wires with the hope of a stall.

Disconnecting a battery on a running vehicle can blow a diode.  It can also damage other solid state parts, voltage spike.  GM found that out in 196something