My Ducati ST4s sometimes stalls. The symptoms are: the engine starts well when it is cold when the engine is slightly warmed up it stalls very regularly when increasing the choke it is noticeable that the engine cannot maintain an idle speed the stalling only occurs at low speeds or when standing still, usually when pulling in the clutch the engine runs fantastically at high speeds In the meantime I have also had twice that the engine did not want to start (no starter motor) after stalling Is the engine equipped with an idle control valve? Is it possible that it is defective?
What year is it? If 2001, it's possibly the ECU - there was a workshop advisory way back when for them and the fix was to install a 2002 ECU instead.
I have heard of some 2001 build bikes being registered in 2002. Does the bike need the starter button holding down till it starts, or does it carry on turning over until it starts after a quick press of the starter button?
They have the biggest impact on the smooth running of the motor when running at low engine speeds, at high revs they have proportionately less of an effect the faster the engine is turning over.
Apologies for a looong reply, but I hope it might help you. I had very similar symptoms with a Morini Granpasso I had. It worked perfectly when I put it in the garage for the winter. When I got it out the following spring time, it would start easily from cold, but stall as soon as it warmed up. Having ridden carburettored bikes and very few fuel injected bikes, I had to quickly learn about F.I. Systems. The reason it starts easily from cold is that it is using the stepper motor that provides an enriched fuel mix until the ECU receives a signal telling it that the engine is sufficiently warm and ready for the ECU to take over with its metered fuel injection determined by parameters being fed by a range of sensors around the bike. However, if I kept the revs above tickover (1400 rpm) the bike ran perfectly, but as soon as the revs dropped to 1400, when the stepper motor is supposed to take over again, dead engine. I changed • stepper motor. No difference • spark plugs. No difference • coil sticks. No difference • rebalanced throttle bodies. No difference It was suggested that perhaps an internal fuel hose had a small split, so the pressure regulator in the tank was playing up. • new ethanol-proof hoses fitted. No difference • new fuel regulator. No difference The bike had had a custom tune/chip to 128 bhp. I took it to the importers, they:-•removed custom tune and chip. No difference •swapped ECU for brand new one. No difference Deflated, I took it home and set about testing continuity on every wire to/from the ECU - all good. I then decided to take it to the previous, time served, importers. They changed many settings, but none made any difference. They swapped the dash from a new bike because the dash houses a heat sensor. No difference. They too had to give up. Because the tank internals and FI system was made up of off the shelf components, they were shared by Ducatis, so I took the bike to a friend who is a Ducati factory trained mechanic and has his own Ducati specialist independent servicing business, who was convalescing at home after a knee op. He also used his factory Texar(?) diagnostic kit that couldn’t find any faults, but we replaced the TPS. No difference. No amount of computer diagnostic hours at my friend’s, or either of the old-school importer, or the new importer made any difference whatsoever, revs dropping to 1400 (stepper motor range) resulted in a dead engine. Cold logic resulting from every failure point having been eliminated meant it had to be a sensor that was feeding a garbled signal into the ECU meaning that the handover from stepper to ECU just wasn’t happening as it should. Eventually, the new importer managed to speak with the head engineer at Morini who confirmed that all failure points had been covered and either been replaced, or eliminated. The fact that it had worked perfectly before being garaged, but not after suggested to him it was a case of GIGO (garbage in, garbage out). He said he thought that during the winter storage, there might be some barely visible corrosion on the end of the camshaft where the camshaft sensor would pick up. He advised it was not a question of cleaning, but polishing the cam. And so it proved to be! Tickover restored.
That sounds about wright what is happening with my ST. Thank you so much. My bike is more than 20 years old, 20 years of rain, dust and corrosion. So, where can I find this sensor on te ST4s? Is it the same place as a 996?
Most likely. When this happened to mine it was slightly better on Higher octane fuel. But the real fix was a visit to Nelly. Total transformation.
IIRC for the 4S if you look behind the water pipe coming out of the water pump, the crank sensor is behind that on the side of the bottom of the vee between the cylinders if that makes sense? Beware if you remove it as they are shimmed to set the gap!!
