Tuned S4Rs stutters below 3K, rough in steady cruising: not the coil, after all

[oldndumb]

They can all be checked with a multimeter.......

Some voltmeters are better than others for checking TPS. I've had better luck using an analog rather than a digital one.

Moronic, I didn't see mention of a PowerCommander or such, but by chance do you have one installed? Reason I ask is because I know of one with a PCIII which had an internal fault with the TPS connection. Symptoms were much as you described. It was allowing voltage from the PC to go to the TPS. A diode in the PC to TPS wire proved the diagnosis.

[Howie]

Yes, an analogue meter, even better, a scope is better than a digital meter on this type of TPS since the digital will not be smooth.  They are getting rare though.

[oldndumb]

Yes, an analogue meter, even better, a scope is better than a digital meter on this type of TPS since the digital will not be smooth.  They are getting rare though.

Low tech is not rare for old timers. 

[Moronic]

Thanks guys for the replies. No, no powercommander. Tune was done directly with Tuneboy, although at pres i am running the alternative ECU I installed as a check, which has the standard DP Termi map and seems quite good when all is well.

But the fact the PC/TPS connection fault gave similar symptoms to mine gives me hope. 

Howie thanks for the VM details. Luckily there seems to be an aftermarket TPS available so I have gone for that. Even if mine had tested okay with a VM, I would still have been suspicious.

New TPS should go in Friday but I will give it some test miles before reporting here.

[Moronic]

Well the new TPS did the trick ... sort of. 

It has cured the poor throttle response and vibration issues. All is much better and I no longer feel like the bike has some mystery gremlin.

I have a pretty good theory about how this got overlooked also. But I will save that.

However she still is not completely happy.    My target at present is the horizontal injector.  Since the bike has now done 74,000km - adding up to nearly 20,000 since the tune when it all went wrong - it could easily have gone downhill since the problems began and I wouldn't have noticed.

I will wait until I am fully satisfied and then do a full write up of what has been a maddening but educational experience.

I certainly know a lot more about how the bike works than i did when this started. And I understand better that, umm, joke about Ducati turning riders into mechanics. 

While I am on mechanics, I want to give a big thank-you to Anthony Warnock at Corse Motorcycles in Perth, Western Australia. His patience, availability to make changes one at a time and - most of all - clear communication has allowed me to get - almost - to the bottom of this.

A big number of other people have been helpful also, including the many commenters on this thread. I will offer more acknowledgment after the final piece has fallen into place. Which unfortunately could take another couple of months.

[itsamonster]

Has there been any progress on this?