Sometimes, not always, I’ve a misfire around 9.5-10k revs. The symptoms are similar to what happens when you hit a rev limiter. So I pull the clutch in, rev the engine with no strain on it, no problem, it revs cleanly all the way through. Let the clutch back out, slow down, drop down a gear or two, accelerate again, this time no problem and no further problems for the rest of the ride. I’d like to think it’s just ‘cobwebs’ that need to be blown away but as this is a piece of electronic & mechanical equipment the concept of cobwebs can’t really exist - can it? Does anyone have any suggestions please as to what might be the cause and where I should start checking first? It’s a 1999MY 748, Done 3500 miles, is fitted with CF Termis and has the correct EPROM fitted. All done by a Ducati workshop at the time of original purchase of the bike. Truth be known it’s not very often I get it into the very uppermost reaches of the rev range as the roads around here are too shite! Usually I’m bimbling along sub 7k, standing on the pegs to use my legs as additional shock absorbers to soak up the many many many bumps in the road but sometimes if I’m lucky I get a nice piece of fresh tarmac with no bumps and no cars
That sounds painful. But, seriously is there an electronic signal from the flywheel to the ÉCU? Also, how could the flywheel work loose. I haven’t checked my workshop manual but is there even a flywheel? Surely it’s the crankcase, crankshaft, con rods, pistons & reciprocating masses therein? No flywheel as such, as in car engines.
There is and the retaining nut is notorious for coming loose. However, if very loose you would probably hear a knock and your mileage is low, so probably not the most likely culprit. I would look at simple things first, such as spark plugs or fuel starvation. Could rust be blocking the fuel filter? An old bike which hasn't done many miles would be prone to condensation in the tank. It might also be water in the fuel. Look at the easy, simple things first I'd say...
Does it have both? I thought only the P8 ecu bikes (early Strada, SP, SPS) had both sensors? Certainly pre '99 single-phase bikes have no flywheel sensor. Not sure if a '99 registered 748 might still be single-phase electrics (I think technically it shouldn't be but you never know how long it took to use up old parts) or 3-phase but I don't think 3-phase bikes had a flywheel sensor either?
You a You are correct, only bikes with the P8 (or P7) ECU have 2 sensors and as far as I know this was never used on any 3-phase engined bike. A failing crank sensor is a very possible cause for a high end misfire.
Thanks guys, I'm digging through the workshop manual now and stand corrected on the flywheel never having stripped one down that far before. Fortunately there was no rust inside the tank, even though it had stood for 7+ years - outside Surprisingly everything was shiny shiny inside the tank - can't say the same for all the nuts & bolts though Fuelling and ignition was cleaned and checked over when I started refurbing her to get her back on the road, although I have to admit as the spark plugs were working fine I didn't replace them. I'll get some new ones and put them in, the current ones are 19 years old after all.
Looking at Cookies answer I think he meant, yes there is a flywheel and yes there is a crank position sensor. Not two sensors. That's how I read it.
@Dukedesmo my post came across wrong mate, i mean it has a crank sensor and the actual fylwheel in the engine conected to the crank, not the two sensor type engine, once i re read my post it sound like i said it has the two crank pick ups.
According to the manual my bike should have a Marelli IAW 1.6M ECU, which it does, and yes there is (or should be) a timing sensor on the left hand crankcase so I'll check that out when I next get chance and make sure its within specifications. Thanks for the advice.
Hi, thanks, I cleaned it up as part of recommissioning her, not that there was any crud on it anyway surprisingly enough.
No I didn’t change it. My mistake on cleaning it. I’m old, I get confused. I was working on a 19 year old Peugeot Speedfight scooter at the same time that also had stood for 7+ years and it was the fuel filter on that I cleaned out. On the 748 I took the pump assembly out of the tank and checked everything over it all seemed ok, especially as the inside of the tank was fortunately like new. Perhaps I should fit a new fuel filter just in case?
If anyone's still following this thread an update is as below. I had an issue with the oil pressure light indicating low pressure, it wasn't low and that issue has now been fixed but took a while for the necessary oil pressure testing eqpt to arrive and then be put into use. Once fixed I went for another ride, now the misfire has moved down the rev range and is no longer limited to the upper rev limits. At times it's as though it's only running on one cylinder, there's some backfiring from the exhaust, which to me indicates unburnt fuel, and then she's fine again. I managed to limp home and thought it's deffo the spark plugs being as old as they are (19 years) even if they haven't done that many sparks (3500 miles). So I ordered two new ones - had to wait 2 weeks for them to arrive at the local motor factors , took out the old ones to see this. Horizontal cylinder. Vertical Cylinder. Which tells me the fuel reaching the vertical cylinder is not being fully burnt off. 'Great' I think, 'it's the spark plugs; this old one is breaking down and not sparking as it should'. New ones get put in, start her up. Same issue. So now I'm thinking I need to trace it back. Could a coil be breaking down? Should I look elsewhere? I think there are other things I should be checking before attacking the timing sensor on the crank. All suggestions gratefully received.
The black and oily plugs shows that it is the vertical cylinder that is misfiring. Since new plugs didn't fix the problem lies elsewhere and since only one cylinder is affected it is unlikely to be the crank sensor. It is easy to swap the coils round and if the misfire moves to the other cylinder then it is indeed a faulty coil.
