My bike died today, and this is what we found...

[flux]

Coming into work today, about to turn onto the side road our shop is on, and the bike died.  Restarted straight away and rolled into the gas station where it died again.  Ran fine with throttle on but would die with no throttle again.  I was only a minute from the shop so I limped it in.  

Once we tore into it and got a computer plugged in we found that the stepper motor had a black mark on the white plastic and when we started the bike a little smoke came out of it.  Not a good sign!  

So, we ordered the parts.  From what Andy, our Triumph tech, tells me, this could be what has been causing my backfiring on decel which has never been 100% fixed and some surging at 4K RPMs that I have been having lately.  

I'm told that if this stepper motor goes out you should NOT run the bike as it could cause catastrophic damage to the engine.  

Looks like I'm out of a bike for a few days but I'm hopeful this will fix the issues I've been having!  



And yes, I am cleaning the throttle bodies while we're at it!   8)

[GWL]

This sounds exactly like my problem.I've got black around my stepper motor too. Just thought it was normal.Did you order the complete stepper motor and housing or just the motor? Please keep us informed as to how you get on.

[flux]

We ordered the motor and the housing, yes.  Figure $150 or so for both parts, US dollars.  

My tech felt very strongly that the bike should not be run if this is the issue.  If you can get to the stepper motor and connect your tank off to the side of the bike, run the bike, open and close the throttle, and watch for a tiny bit of smoke escaping from the hole.  I can't imagine that being a good thing.  

I will keep you updated... may be a week before it's all buttoned back up.

[tett]

Very interesting.  A true stepper motor does not have any brushes or sparking parts.  I don't understand how it could fail in this manner.

I design mechanical assemblies which use stepper motors and we purchase thousands each year of many styles?  Curious how they could fail like this

What is the stepper motor's purpose?

Cheers!

tett

Coming into work today, about to turn onto the side road our shop is on, and the bike died.  Restarted straight away and rolled into the gas station where it died again.  Ran fine with throttle on but would die with no throttle again.  I was only a minute from the shop so I limped it in.  

Once we tore into it and got a computer plugged in we found that the stepper motor had a black mark on the white plastic and when we started the bike a little smoke came out of it.  Not a good sign!  

So, we ordered the parts.  From what Andy, our Triumph tech, tells me, this could be what has been causing my backfiring on decel which has never been 100% fixed and some surging at 4K RPMs that I have been having lately.  

I'm told that if this stepper motor goes out you should NOT run the bike as it could cause catastrophic damage to the engine.  

Looks like I'm out of a bike for a few days but I'm hopeful this will fix the issues I've been having!  



And yes, I am cleaning the throttle bodies while we're at it!   8)

[ChazzyB]

What is the stepper motor's purpose?

Controlling air for idling, I think. Three tubes come out from the housing, each running to one of the throttle bodies. The top of the housing mates with the airbox.

[flux]

The easiest way we found to explain it is that its a moving fuel screw.

I forgot to mention that my throttle bodies were out of alignment as well.

[Bixxer Bob]

What is the stepper motor's purpose?

Controlling air for idling, I think. Three tubes come out from the housing, each running to one of the throttle bodies. The top of the housing mates with the airbox.

More or less.  The stepper motor operates the Idle Air Control Valve (IACV).  With the throttle butterflies closed almost no air gets to the engine, so it would stall (it doesn't have idle jets like carbs) so the ICAV does the job of the idle jets by allowing air past the white bit in the valve into the slots just below it and then on through the three tubes mentioned and into the throttle bodies where it mixes with the fuel from the injectors.  The fuel map in the Engine Control Module (ECM) tells the ECM the target RPM for the current engine temperature. The ECM opens the IACV then checks the RPM via the crankshaft sensor.  If the RPM is too high, it closes the valve a little,  if the RPM is too low, the ECM opens it a little.  This happens many times a second thus maintaining  the tickover close to the target RPM.  The fuel map target RPM drops in stages from around 2000 at -10 deg C to 1200 at 90 deg C and above.  There's also a table to richen the fuel mix at low temp but that's not important here.

Incidentally, if you're a Tuneboy tinkerer like me, you have to be careful altering the fuel map at "0" throttle and 0-2000 rpm.  If you put too much or too little fuel in there the IACV can't maitain the tickover correctly because - as I've tried to explain above - the fuel at "0" throttle is constant and the revs are controlled by the IACV.  If you richen it too much the tickover is high when cold and feels a bit flat or gutless if you're trying to inch the bike around at low revs.  If you lean it out too much it'll be lumpy and cut out or stall easily at tickover.

[tett]

Excellent answer.  Thanks!  Great to know these things.  This is my first bike with EFI and it is fascinating.

May look into getting a tune boy.  Hard to justify now as my bike runs great but I do want to get a more throaty exhaust and then I may need to re-map.

Now, as for the question of why the stepper is failing.  I still don't understand how it can get a carbon deposit around it.  There should be no arching coming from a BLDC motor.

Cheers!

tett

What is the stepper motor's purpose?

Controlling air for idling, I think. Three tubes come out from the housing, each running to one of the throttle bodies. The top of the housing mates with the airbox.

More or less.  The stepper motor operates the Idle Air Control Valve (IACV).  With the throttle butterflies closed almost no air gets to the engine, so it would stall (it doesn't have idle jets like carbs) so the ICAV does the job of the idle jets by allowing air past the white bit in the valve into the slots just below it and then on through the three tubes mentioned and into the throttle bodies where it mixes with the fuel from the injectors.  The fuel map in the Engine Control Module (ECM) tells the ECM the target RPM for the current engine temperature. The ECM opens the IACV then checks the RPM via the crankshaft sensor.  If the RPM is too high, it closes the valve a little,  if the RPM is too low, the ECM opens it a little.  This happens many times a second thus maintaining  the tickover close to the target RPM.  The fuel map target RPM drops in stages from around 2000 at -10 deg C to 1200 at 90 deg C and above.  There's also a table to richen the fuel mix at low temp but that's not important here.

Incidentally, if you're a Tuneboy tinkerer like me, you have to be careful altering the fuel map at "0" throttle and 0-2000 rpm.  If you put too much or too little fuel in there the IACV can't maitain the tickover correctly because - as I've tried to explain above - the fuel at "0" throttle is constant and the revs are controlled by the IACV.  If you richen it too much the tickover is high when cold and feels a bit flat or gutless if you're trying to inch the bike around at low revs.  If you lean it out too much it'll be lumpy and cut out or stall easily at tickover.

[flux]

I don't know the answers to these questions.  It is just way over my head, I will admit.  All I know is what I see.  And what I see ain't good.

For interested parties, here are the part #s of what we ordered.

T1240888
T3600037
T1241064
T1241063

I am very hopeful that this might fix my backfiring, and the flame that has been shooting out of my exhaust on occasion.  Not to mention my little surging at about 4K RPM.  We shall see...

[Bixxer Bob]

The blackening is more likely to be carbon deposited as evidence of backfiring through the inlet valves than from the motor.  I'd be thinking initially pre-ignition but unless you have a custom map that's not likely unless something else is wrong.  I remember mine backfiring out of the throttle bodies once when I was tinkering with a map but I'll have to put my thinking cap on to remember what I was doing..... :roll:

Edit.

Right, had a think and a couple of things spring to mind.  If your valve shims need doing and an inlet valve has no clearance (remember these are shims not tappets - shims the gap closes where on the old tappets they usually got bigger) the valve may not be closing properly letting gas back into the inlet.  Since it's only occasional,  this is not very likely.

Next, if it's really lean then the gases don't burn completely and could still be burning as the inlet valve opens giving a pop through the intakes.  With the throttle closed that would be directed throught he IACV.  The same condition, ie lean, can also cause popping on overrun, again because the burn is too slow, so unburned fuel gets into the hot exhaust and bang! so this is a possible scenario.  Why it's lean is a whole other science though.  You tech could do a quick exhaust analysis to tell you if it is lean, but it really needs O2, CO and CO2 to fully understand what's going on.  

Possible causes of lean are, wrong fuel map (after market exhaust and standard map for instance), IACV stuck open, throttle body air leak, IACV hose air leak, faulty O2 sensor in the exhaust (tech can also check for this quickly) it should be 0.46volts ign on engine off.  this fault would also show the long term fuel trim very low or even negative (mine is around 4.2%,  lower than 3.5% and it starts popping through the intakes and dying on tickover).

Hope that's given you and your tech something to think about...  

[flux]

Bob, nice theories.... I passed this onto my tech, will let you know what he says...  this stuff is way over my head!   :oops:

[flux]

Well, after 3 long weeks, it appears my bike might be ready to roll again.  

The housing for that stepper motor had a hairline fracture in it.  After replacing, the bike is once again idling just fine, at least, so far.  Also, 4 valves were so tight a feeler gauge couldn't be slipped in.  I just had my valves checked 3000 miles ago, too, so either they weren't done right or something crazy happened.  Either way, they are good now.  Its pouring and freezing today so I have yet to really ride it but all signs are positive.  

Stay tuned...

[walker]

mine had some staining like yours - but was fine. I took it apart - there is a motor that spins a threaded rod, which controls the gap in that top part in the picture.... and the threaded insert for that cap is plastic....  I had checked mine a while ago, and it looked fine, so I just cleaned it off a bit and put a new dab of grease in there on the threads (it comes that way, so I just put it back as is...)

I also checked mine for cracs where those hoses connect to the intake - mine were fine, but that could be a problem area too.

let us know how it rides - affirmation of the fix!