2017 Stelvio running issues

[Twin AH]

7 minutes ago, pete roper said:

It’s still showing all the signs of not firing erratically on one cylinder at least. The lack of power, the very high fuel consumption, the smells unburnt fuel, all point towards one or both cylinders only working sporadically.

The plug caps are a known problem area so it was a logical place to start. Now you need to go deeper.

Does the dash blank out or the lights flicker when it’s surging and misbehaving? Try hooking up a strobe to the plug leads and riding it to see if and when the spark is dropping out. 
 

Check and swap around the relays and clean all the fuses, including the ones under the small triangular panel under the seat on the RH side. Clean the battery posts and the cable connectors and ensure the earth strap is clean and securely attatched to the mount on the gearbox inboard of the starter motor cover.

With the bike on its centrestand and the ignition on turn the handlebars slowly from lock to lock and see if the lights or dash flicker.

Something is causing it to drop at least one cylinder. It’s simply a process of elimination to work out what it is.

Hey Pete         No the dash and lights all function as they should when its having its fits. Battery is new that was my first go to on this issue.

Will check earth strap tonight.

If its electrical voltage issues to the ignition portion wouldn't it fall even farther on its face under load and RPM increases, such as a bad coil or???

Vacuum leak some where?

[PJPR01]

7 minutes ago, Twin AH said:

Just caps at this point.......... new plugs should arrive tomorrow.

Original fuel filter. Yes did give it a good does of injector cleaner a couple weeks ago(that was my first thought on what it might be)

I'm thinking from time to time now the way it is acting that has anyone had a vacuum leak some where in the system that could be causing all this?

It still has all the original pollution control/evap can ect.

 

Just trying think of all the easier tests to do first is all.

Ciao

Got it...have you pulled the plugs to see what they look like, any difference between left and right...one sooty looking, one nice and brown/tan?

[Twin AH]

57 minutes ago, PJPR01 said:

Got it...have you pulled the plugs to see what they look like, any difference between left and right...one sooty looking, one nice and brown/tan?

Yes,,,,,,,,, both look identical nice brown color

[Twin AH]

Just replaced plugs with new ones ....... no change 

We got to be getting down to the bottom right?

What's left...............?   Engine out and replace

Thx to all in advance

[PJPR01]

Eliminate old gas and put a fresh tank in or add some fuel treatment.

 

Fuel filter would be next…but first I would also connect Guzzidiag and see if you have any obvious errors or faults popping up.  You might also have a faulty air temp sensor on the air box that regulates fuel air mixture, a bad coil…but without seeing if there are any errors registered we’re just guessing.

Edited October 21 by PJPR01

[Twin AH]

20 minutes ago, PJPR01 said:

Eliminate old gas and put a fresh tank in or add some fuel treatment.

 

Fuel filter would be next…but first I would also connect Guzzidiag and see if you have any obvious errors or faults popping up.  You might also have a faulty air temp sensor on the air box that regulates fuel air mixture, a bad coil…but without seeing if there are any errors registered we’re just guessing.

Only one error and Pete said its nothing.

Fresh fuel was put (premium) within hrs. of the event........... got it Coil or air box sensor.

Any way I can do a quick and dirty test to identify if the airbox sensor is on the fritz?

[Twin AH]

On 10/19/2025 at 1:50 PM, pete roper said:

I don’t think Mark posts here. What’s it doing?

Hey Pete not sure if everyone was made aware of the very beginning of this issue as I mentioned to you with the full engine shut down and coasting to a stop at the side of the highway with dash notification saying....ECU miscommunication with dash.... cycled the key and everything started up and I continued on back home and replaced the battery. Has not done that since if that helps in identifying what the present issue/s might be.

 

Ciao

[PJPR01]

14 minutes ago, Twin AH said:

Only one error and Pete said its nothing.

Fresh fuel was put (premium) within hrs. of the event........... got it Coil or air box sensor.

Any way I can do a quick and dirty test to identify if the airbox sensor is on the fritz?

Unfortunately I don't know of another way.  Now knowing that you had a full shutdown, I would definitely be hooking up Guzzidiag and reading ECU errors or Dashboard errors thru the Diagnostics Menu.  Do you have Guzzidiag?  I'm hoping you haven't dropped a valve here.  How many miles on the bike?

Edited October 21 by PJPR01

[pete roper]

Whoa, whoa, whoa! Hang on a minute. Let’s not start jumping to conclusions of disaster! If it ticks over and runs fine up until a certain point, (3,500?) it hasn’t dropped a valve. Believe me, if it drops a valve it wont run for long!

Now, the ECU disconnect message is a concern as it shows that power, (Or earth.) has been lost to the ECU. If though, it was a poor connection causing voltage flutter and it had somehow damaged the ecu it would usually cause a complete and immediate shutdown and even if it somehow, miraculously, only affected one of the ignition trigger circuits it wouldn’t only start doing it at higher rpm, it would be dead on that side completely. That’s why I’m still convinced it is spark related as both ignition and injector pulse are triggered from the same source and the fact that it stinks of fuel when only running on one tells us that the injector is working just fine.

Now as I suggested connecting up a strobe will allow you to see which side it is that is dropping spark. Then simply swapping the coils over will enable you to diagnose a duff coil. If the spark loss moves to the other cylinder? Then it’s coil. If it stays where it was, it isn’t!

Likewise I think phase sensor is unlikely. If it was going to be problematic I’d expect it to effect both spark and fuel delivery on both cylinders rather than one and from the description it certainly sounds as though it’s running full time on one and part time on the other, but only above that certain rev point.

I’m assuming that all the stuff like valve clearances have been checked and nothing untoward was found?

Obviously I’m half a world away so I’m stumbling around with one hand behind my back but this sounds electrical/spark related, not catastrophic or *mechanical* in origin. The devil is n the diagnosis. I think it will, once identified, be a simple and easy fix unless it’s a break somewhere in the bowels of the loom.

[Twin AH]

2 hours ago, pete roper said:

Whoa, whoa, whoa! Hang on a minute. Let’s not start jumping to conclusions of disaster! If it ticks over and runs fine up until a certain point, (3,500?) it hasn’t dropped a valve. Believe me, if it drops a valve it wont run for long!

Now, the ECU disconnect message is a concern as it shows that power, (Or earth.) has been lost to the ECU. If though, it was a poor connection causing voltage flutter and it had somehow damaged the ecu it would usually cause a complete and immediate shutdown and even if it somehow, miraculously, only affected one of the ignition trigger circuits it wouldn’t only start doing it at higher rpm, it would be dead on that side completely. That’s why I’m still convinced it is spark related as both ignition and injector pulse are triggered from the same source and the fact that it stinks of fuel when only running on one tells us that the injector is working just fine.

Now as I suggested connecting up a strobe will allow you to see which side it is that is dropping spark. Then simply swapping the coils over will enable you to diagnose a duff coil. If the spark loss moves to the other cylinder? Then it’s coil. If it stays where it was, it isn’t!

Likewise I think phase sensor is unlikely. If it was going to be problematic I’d expect it to effect both spark and fuel delivery on both cylinders rather than one and from the description it certainly sounds as though it’s running full time on one and part time on the other, but only above that certain rev point.

I’m assuming that all the stuff like valve clearances have been checked and nothing untoward was found?

Obviously I’m half a world away so I’m stumbling around with one hand behind my back but this sounds electrical/spark related, not catastrophic or *mechanical* in origin. The devil is n the diagnosis. I think it will, once identified, be a simple and easy fix unless it’s a break somewhere in the bowels of the loom.

Thx Pete................... ya this seems like a fueling/electrical issue from my limited experience with these monsters.

I have at this point checked valves and they all seem to be within specs but I guess I'm going to need a new coil to switch around and see if it shows one of them is at fault.

I really do appreciate you as well as all of you for chiming in here and trying to diagnose.

Ciao

[pete roper]

ASI said, no need to buy another coil at this point. Use a strobe to ascertain which side is dropping out. Swap the coils side for side. If the problem transfers to the other cylinder you’ll know it’s the coil. I really doubt it will be though.

The important thing now is to establish if it’s one or both sides dropping out. I reckon it’ll be one. Do the coil swap. If it continues to be dodgy on the same side you can plumb in an LED to the coil trigger wire to see if it’s getting signal. If it is but the spark is still dropping out then it has to be coil. If the signal to the coil is dropping out? Then the issue is further back and you’ll need to start back-probing the loom.

[Twin AH]

9 hours ago, pete roper said:

ASI said, no need to buy another coil at this point. Use a strobe to ascertain which side is dropping out. Swap the coils side for side. If the problem transfers to the other cylinder you’ll know it’s the coil. I really doubt it will be though.

The important thing now is to establish if it’s one or both sides dropping out. I reckon it’ll be one. Do the coil swap. If it continues to be dodgy on the same side you can plumb in an LED to the coil trigger wire to see if it’s getting signal. If it is but the spark is still dropping out then it has to be coil. If the signal to the coil is dropping out? Then the issue is further back and you’ll need to start back-probing the loom.

Understood............. Any value in posting up a short video clip to possibly make the situation a bit clearer? Never done that before on this forum either.   

[Twin AH]

2 minutes ago, Twin AH said:

Understood............. Any value in posting up a short video clip to possibly make the situation a bit clearer? Never done that before on this forum either.   

Also just for the record while I had it running in the shop the other day I did pull the plug on the air box air temp sensor and it didn't seem to change anything??

[gstallons]

Don't worry too much about that. You can measure the resistance of the sensor and record the value + the ambient temp. if you have another guzzi close, check it. If not post these #s and we will check and compare the values.

[PJPR01]

2 hours ago, Twin AH said:

Also just for the record while I had it running in the shop the other day I did pull the plug on the air box air temp sensor and it didn't seem to change anything??

With a faulty air temp sensor, my Norge ran like crap...noticeably bad, couldn't get above 30-40 mph.  New sensor, all is good.  It's a cheap part, and easy to install...worthwhile checking.  Visible inspection and cleaning with MAF spray didn't fix it, so a new sensor went in.