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  #1  
Old 07-Jun-2003, 07:24 PM
Wadd Wadd is offline
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INTERMITTANT MISFIRE ON 998S

My 998s which is 4 months old with 2000 miles had developed an intermittant misfire at about 6 - 7000 revs.

It only does it very irregularly (about once every hour of riding), its like the engine cuts for a split second and then it returns to normal.

I originally thought it might be the petrol but I have since filled up with fresh petrol and it did it again this afternoon whilst i was in the procerss of overtaking !

Has anyone got an idea of what might be causing it and where to start looking. I know its under warranty but my nearest dealer is 40 miles away and im hoping it might be something simple

Wadd
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Old 07-Jun-2003, 07:41 PM
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rcgbob44 rcgbob44 is offline
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Miss Fire!

Greetings!
I have a 998s Mono which i am still running in, since fitting my 50mm Termi`s i to get the odd momentary missfire just after its been run hard, i have put this down to a hot enging and possible fuel vapour problems, but only occasionaly, I have recently fitted carbon ait tubes and a JHP filter system and since doing this it appears to happen less frequently!! i would suggest you get to your dealers ASAP if it still persists, I am quite happy to live with the occasional clitch, and it is very occasional, as a trade of for the increased performance resulting in fitting the pipes and filter, Give the guys at ProTwins in Godstone a ring for some advice.
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Old 08-Jun-2003, 04:52 PM
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DSC Member Shazaam! Shazaam! is offline
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The engine management system uses a throttle position sensor to monitor throttle input so the computer can supply additional fuel to the engine when you turn the throttle grip. This sensor's resistance changes as you vary throttle opening from full-closed to full-open much like the volume control knob works on a radio.

And just like a radio with an intermittent scratchy volume control, the throttle can occasionally send a full-closed (no gas) signal even though you have opened the throttle. This gives you a dead spot or drop-out in the throttle. Contact cleaner works fine for volume controls, but the throttle position sensor (TPS) is sealed to prevent water from getting-in, so a faulty unit should be replaced.

Keep in mind that an open TPS circuit gives a fail-safe closed throttle signal. So before replacing the TPS, first clean and tighten the connectors between the TPS and the computer. An intermittent open (non-conducting) electrical connector will also be the cause of an occasional dead throttle condition.
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Old 08-Jun-2003, 05:07 PM
DJ Tera DJ Tera is offline
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Shazaams avatar says it all!
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Old 09-Jun-2003, 01:32 PM
Damo Damo is offline
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Had the same problem on mine. If you can check out the rev counter while its happening, if it's the same problem it'll drop to 0rpm. I had the following changed..
Ignition switch/Lock
TPS
ECU
After 12 long months and virtual dispair, it was the crank position sensor, not faulty but just needing repositioning.
I'm pretty sure that's what it'll be!

Keep me informed..

Damo
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Old 09-Jun-2003, 07:08 PM
Wadd Wadd is offline
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Spoke to Ducati London South today who said that its nothing to worry about they have had this problem with a number of customer bikes recently and its due to the Termis. The race cans and ECU dont work properly at constant revs (6000-7000 revs in 1st gear doing 30mph) and its just something im going to have to live with. The race ECU and cans are designed for a constantly changing amount of trottle which would be used on a race track ie either accelerating or blipping or closed and not held in one position for any length of time.

Anyhow i,m going to monitor the problem to see if it improves or gets worse.


Wadd
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Old 09-Jun-2003, 07:14 PM
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Talk to another dealer, or (better still) a Ducati tuner who knows his craft.
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Old 09-Jun-2003, 08:06 PM
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chillo chillo is offline
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I've been suffering with a 'regular' misfire on my 998R at around 8.5-9.5k since new.
It wont rev past 9k in top (indicated 160mph).
It will rev through to just over 10k in lower gears.
Had the crankshaft position sensor adjusted and it felt a bit better, but its still not right. Spoke to John Hackett and said he had seen a few 998R's with this same misfire. Turn out to be a faulty CPU.
Got a replacement to be put in when my bike has its 6k service in a couple of weeks. Hope this will cure it!

Was chasing a new 2003 GSXR1000 on sunday and was sat on his exhaust pipes upto 160mph He kept looking in his mirrors as he was nailing it on the straights prbably thinking how the hell is that ducati staying with me!
Looking forward to getting it cured
Don't know if this is something you should check on yours?

[Edited on 9-6-2003 by chillo]
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Old 09-Jun-2003, 08:15 PM
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There is a small inherant glitch with the weber-marrelli ECU whereby,at a certain RPM under certain conditions, it doesn't know which way it's @rse is and this shows up as a slight surging or hunting.
It's usually around 4500-4800 under part throttle cruising.
The ECU can't decide whether or not the bike is accelerating, cruising or braking and it's switching in and out of it's various maps.
When you say it did whilst overtaking, this puts it firmly in the accelerating map, so it should be OK.
I'd get the bike plugged up to the test equipment the dealers have, or as Shazzam says.........get a second opinion.
The crank sensor is a possibility as is the TPS, especially if the bike plays up when it's warm, say in slow moving traffic??
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Old 11-Jun-2003, 06:16 PM
Wadd Wadd is offline
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When I said it did it whilst overtaking ,I was actually not accelarating, I was going at a constant speed as I was overtaking a long line of cars and had already reached the required speed.

I'll see what happens over the next week or so, if it gets much worse i'll get it checked out somewhere else


Thanks for the advise
Wadd
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