Hi guys! I've got a misfire on my 1997 748 that's suddenly appeared in the last couple of days. The bike starts fine and idles OK initially. Once moving the misfire generally appears between 1.5-6k-ish rpm, generally on part throttle. If I accelerate quickly it's smooth, but it does feel down on power all through the rev-range (slightly). I don't think the misfire is existent at high speeds/high rpm - I can be in 4th @ 70mph, on part throttle and try to accelerate and it doesn't have that get-up-and-go that it used to. Now, there are two things that could have been the cause: Washed it two days ago - most likely, I'm think water ingress into a connector somewhere - though I did spend an hour disconnecting all the connectors and spraying electrical spray and it hasn't made a difference. I was quite low on fuel and got a tank full two days ago - could be a bad batch? One other thing I guess I should mention is that ever since I got the bike several months ago, occasionally it will cut out for a tenth of a second. Just a very slightly 'murmur' like I've closed the throttle lightning quick and opened it again. But then this misfire has come on only in the last two days and relatively suddenly so I don't think the two symptoms are related. I've got a list of things to check: going to visually inspect the HT leads (which I did yesterday quickly and they looked OK) as well as the spark plugs. Measure the resistance of the coil packs and HT leads Inspect the TPS Anything else I should look at? Also
water in spark plug orifice is high up the list, unlikely to have got any in the vertical one. If you inspect the front lead carefully near spark plug cap you might see signs of it breaking down. I always have a good spare to try as it's easiest to swap it just to rule it out. Occasionally a plug will break down with similar symptoms but rare. Do you have the standard large 'void' sticker completely covering your rubber 'chip access' grommet on your ECU? - that or a strip of 'gaffer' tape. It's easy for the ECU to take on water even with the bung in place.
Hmm, possible blocked injector, but the washing thing can cause havoc!, As Chris mentioned, ingress around plugs or coil pack would be the starting point for me too. Let us know how you get on....
Have you checked in the petrol tank for water? I had a sudden loss of power on my 748 once, sort of felt like a "limp home" mode. It went away overnight and then returned the next time I braked hard on a bumpy bit of road. Anyway, I shone the trusty maglight into the tank and spotted some fairly sizeable "jellyfish" of water skulking around in there. Drained the tank (captured about half a pint of nasty rust coloured water), changed the filter and all was well. It turned out that the drain tube had kinked after the Y-section (careless tank fitting) meaning that the drain from the filler recess was returning into the tank via the breather pipe rather than flowing away to the underside of the bike.
have had similar on several bikes indie - good point. A rare breed of owners ride in the rain so not written up often Both times mine was a partially blocked drain tube at the top and visible with the fuel cap open (where the drain tube is attached inside the tank). If I had opened the fuel cap mid-torrential rain (but why would I?) I would have seen what was happening as the water level rises until it can enter the tank via the air vent within the cap. Because the water has disappeared usually when you next top-up you are often not aware of the problem. This applies to all bikes fitted with the 'air vent in filler cap' design. Mine happened on a 748 and a 750 Elefant. You can carefully 'rod' the obstruction through normally but whatever you use needs to be blunt as you could tear the flexible hose as you plunge through the obstruction usually at the top.
Don't forget to check the ignition relay, the yellow 40A one next to the lower left hand side of the battery.
No luck so far unfortunately. Had the forward spark plug out and it appeared fine, although the gap was on the large side so I've redone it to just over 5mm. Had apart and cleaned up all the connectors and relays around the battery and the ECU. The ECU clip isn't amazingly secure, but everything was nice and dry. Got two lengths of duct tape over the ECU too - haven't yet peeled them off to look through the little window. Opened the fuel tank and no sign of any water or anything other than petrol. It's odd really, there's no backfire, but if I rev the engine slightly, shut off the throttle and open it relatively quickly again I can just hear it kind of go "pfft" into the throttle body. But only infrequently. The other thing that might suggest something is up is that after starting it up for 2-3 minutes, the nearside exhaust was smoking, but not the offside. Going to get the vertical spark plug out now and look at the condition of that, as well as get the multimeter out on a few of these sensors!
I had a grub screw, presumably there for vacuum gauges, fall out of one of my inlet manifolds. I've got no pictures but there's one either side in the aluminium of the inlet manifold. Had what i thought was a misfire, bit down on power and got the 'pfft' noise you described. Don't think too much about exhaust sides, they link together by your right foot. It's not like one is for horizontal and the other for vertical pistons.
I have a look for those grub screws, thanks! Went down to my local dealer today to get some service parts. Talk to one of the guys about the problem, mentioned that it might be a blocked carb jet - as apparently there are three per throttle body, one for idle, one for low rpm and one for high? So got some Redex to blast through it - though normally I'm not keen on using stuff like that.
Well this is getting pretty boring, pretty quickly! Things I've checked: HT Leads - seem to be in good condition, but will be changed when I can get some replacements. Spark plugs - not changed yet either but there was no sign of water ingression. Coil packs - no sign of water and resistance from the plug to the HT Lead connector was 3150 and 3180 Ohm. TPS - no sign of water and voltage when ignition on is 4.91V and voltage seemed to be within spec across the throttle going to a max of 4.71V. ECU - no sign of water around the plug. Tank - Got a new fuel filter to fit, but no sign of water in the tank. On new/different petrol as of about 10-15 miles ago. Some Redex had no affect. All relays and connectors - all the ones I've found so far have all been cleaned up. Several around the battery were a bit dirty and grimy, but now cleaned up. No sign of any leak from the throttle bodies or manifolds, no obvious screws or bungs missing. Seems to be getting to be a bit of a fools task just going round the bike and cleaning and changing things in the hope that something will fix it. So I'll be ordering a cable on Monday and downloading the Ducatidiag software to see what the ECU is reading. I'm hoping that will give me some clue as to what is wrong...
Have you tried changing the chip in th ecu? I had a problem several years ago where the bike (a 2002 year 748) pulled away fine but as soon as it got to 8K revs it just cut as if the ignition turned off. Changing the chip cured the problem and it's been fine ever since. Quick and easy to try.
J. B. - you have to actually change the plugs and leads before you can 'cross them off the list' unless you have X-ray eyes :smile:. The only good thing about an unsolved running mystery on here is that it (hopefully) purges everyone's past memories - I had a 748 that I tuned as per the book but then started to suffer similar symptoms to you but more around idle speed - never as high as 6K. Long story short, turned out to be too lean at the bottom end allowing for a less than perfect engine - as a last resort there is a pot in the ECU that you can act on which will help to enrichen things - you can swot up on adjusting this as it needs extreme care (and good eyesight) to avoid damaging. The trick is to write down/draw a picture of the adjustment position before you touch it so you can always return it to this setting if worse/no improvement. Another unusual fault (which 1037 reminded me of) - there is a plugged tapping in each exhaust header to fine tune running and these can (quite rarely) rust through or be missing completely. Symptoms are rough running mainly around idle. Only takes a few seconds to check. Aftermarket etc may not have them.
I had a similar problem, but it did get progressivly worse as the bike ran for longer - turner out to be a dead battery, replaced it and the bike ran sweet as a nut after, however, i later dicovered the recifier has now also gone!
Haha, but it's OK, because I spoke to the leads and they told me they were in tiptop condition! :wink: Will be changing the plugs today, haven't been able to get the leads yet. Got my ECU lead today though so I'll be able to hook up the laptop to the ECU and see if any of the sensors are awry. I didn't really want to start trying to tune the engine because the bike was running fine before, it suddenly started misfiring and nothing had been changed with the setup - so to change that would just introduce another variable.
