Interesting new problem

[Dirty Duc]

I'll get to troubleshooting it later, but for now we can start guessing on the internet to let me brainstorm with the smart folks who hang around here.

06 S2R 800, 44k on the chassis and wiring harness, maybe 20-ishk on the engine.

I'm bombing down the highway at about 65mph, and it starts surging and coughing a little. Get to where I'm going without too much drama, and it does on its own in the parking spot. Quick restart to confirm it runs and I don't need to call the cavalry, and I go inside to do my business.

Come back out and fire it up, and it sounds a little off. No matter, won't get back to work trying to figure that out... But it turns out it's running on one cylinder until about 1/4 turn on the throttle... Then the other one comes back. Ride back to work, ride home at the end of the day.

Right at the transition from one to two cylinders, it's a little choppy and stuttery, as if that isn't an on/off transition. It's definitely getting fuel, because I can smell it at the stoplight as it idles on one.

My current suspects are the tps or the ECU.

[ducpainter]

Could be a lot of things.

When was the last plug change?

[Dirty Duc]

It's been a while. I've got some fresh ones laying around somewhere in the workshop. I'll check them first.

[ducpainter]

Start with the easy stuff.

See what happens.

[Speeddog]

Regarding the TPS, it's the most odd thing, and I've no concrete explanation for it.

The major things that the ECU looks at are the rpm and throttle position.
It's what the ECU uses to look up in the maps what the fuel and spark should be.

So one would think that if you *unhooked* the TPS, it wouldn't run at all.
There's rows and columns in the map, and if you've only got the row number, there's no way of knowing which column to find and extract the cell value.
ECU should absolutely have no clue what to do.
But no, no, no....
The bike will actually run, and furthermore it will run pretty freakin well.
It'll be totally rideable, and really only feel very poorly tuned.
It is obvious it's not right, but it's not that far off.

So dead TPS does not mean dead bike.

I suspect that there's some sort of default code that gets run to generate a SWAG throttle position, so it's then got the column and can go look in that cell.



Like dp said, start with the easy stuff.
If it's acting up, try to determine if the problem is in one particular cylinder, or both.
Those two things can cut the number of possible perps by quite a lot.

[greenmonster]

Regarding the TPS, it's the most odd thing, and I've no concrete explanation for it.

Isn`t that the Limp Home mode that ECU`s have to get you home even if a sensor etc fails?
As you say running a bit off but works.

[Dirty Duc]

New plugs didn't fix it. There's a slight whistle at idle from the horizontal (my hearing is better when I haven't just gotten off an unmuffled Ducati), and it's definitely the horizontal not firing. Vertical header was HOT, horizontal was not.

I'm picking up the compression tester I should have picked up years ago tomorrow. It's not just for this problem, this problem is just the prompt (or excuse to buy tools).

Current theory is some slacker let the belts get too loose and touched a valve to the piston (probably while engine braking, to speak of other bad habits).

[koko64]

Hmmm, the whistle of escaping gas or sucking air..
Check the inlet manifolds for a tear/leak. A manifold leak may let it run at higher revs but cause it to faulter down low. I hope it isnt air passing a bent valve, unlikely as the belt would have to be very very slack indeed.

Otherwise its ignition so a plug lead or somesuch not arcing across a gap at low revs.

But the whistle is the key symptom.

[Howie]

Hmmm, the whistle of escaping gas or sucking air..
Check the inlet manifolds for a tear/leak. A manifold leak may let it run at higher revs but cause it to faulter down low. I hope it isnt air passing a bent valve, unlikely as the belt would have to be very very slack indeed.

Otherwise its ignition so a plug lead or somesuch not arcing across a gap at low revs.

But the whistle is the key symptom.

 

Head gasket leaks usually don't whistle.