Ducati 748 with the most reliable missifre :( - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 27 (permalink) Old Aug 21st, 2016, 9:35 pm Thread Starter
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Ducati 748 with the most reliable missifre :(


I have a 2002 Ducati 748S with 40,000 miles, that I've owned for about 6 years now. In the last year or so the bike has developed a very bad surging/undulation that I assume is a misfire. I am the second owner of the bike and it has always been serviced on time, also by the the previous owner of the bike who gave me all of the old service records. Sadly the bike has been dropped twice (at low speed, ~15mph, by me) _after_ the issues developed, so I don't thinking the accidents left any serious damage. The misfire is present at all RPMs, yet does not cause long cranks, stalling, or back firing of any kind. The bike is almost ironically 100% reliable. The "misfire events" increase with RPM but do not cause the engine to break up. I ride the bike a few times a week to work, to keep it from sitting, so it always has fresh gas and oil changes.

What my mechanic and I have tried over the last year:

*Cold compression test: 149PSI rear, 145PSI front (did this today)
*Verified timing
*Verified the woodruff key on the layshaft did not shear
*Swapped ECU with a similar bike (using same EPROM)
*Swapped tank and pump with a similar bike
*Swapped throttle bodies and injectors with a similar bike
*Replaced the wiring harness with a low mileage used harness
*Replace the CPS with a new unit
*Verified CPS gap
*RPM drop test, vertical cylinder is potentially low contribution? When unplugging the coils, the rear cylinder makes less of a difference in RPM when unplugged.

I can get pictures of the spark plugs if anyone is interested. I can also get audio/video of the bike, I believe the "misfire" is very audible, the bike just doesn't sound right.

Everyone who has worked on the bike is at total loss at this point. Obviously a lot of parts were temporarily substituted yet did not yield a positive change, so I am starting to wonder if it is a compound issue, or if some of the tests should be attempted again. Unfortunately I don't have another Desmo but I might be able to get parts to swap. Any input/direction/ideas/comments/thoughts are more than welcome!

Thanks in advance
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post #2 of 27 (permalink) Old Aug 22nd, 2016, 9:47 am
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Did you try new coils?

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post #3 of 27 (permalink) Old Aug 22nd, 2016, 10:12 am
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So the second tested tank and pump came as unit? So fuel filter was new?
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post #4 of 27 (permalink) Old Aug 22nd, 2016, 10:19 am
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Have you tried switching brands or grades of fuel? Using ethanol vs. non-ethanol?

Air filters are clean? There isn't a mouse trying to live in the air ducts or exhaust?
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post #5 of 27 (permalink) Old Aug 22nd, 2016, 12:37 pm Thread Starter
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Hey Guys, thank you for the quick replies!!

@Warp Racer , Unfortunately I've been working on this thing for so long I don't remember if we tried new coils or plugs. I was thinking about just doing a spark test. Or should I just swap out the coils/wires considering they are relatively cheap?

@miolta , the shop I had the bike at had 748 or 916 without issues, so my mechanic tried swapping some parts from it, so none of the parts were new (sorry for the confusion) I assume the tank was removed as a unit and installed on my bike. Theoretically any of these parts from the donor bike obviously could have had their own issues. I am totally up for sourcing new/used parts. I just don't want to blindly throw parts at the bike.

@dwizum , I moved about 25 miles recently so I now go to a "different" gas station (Shell vs Arco) but I think the whole bay area is served with the same gas. I don't remember if I tried premium (91 here in Cali) I'll ride it this week and put 91 in it. I don't think the stock fuel system on the 748 can move enough fuel to run E85, but correct me if I'm wrong. I was going to try mixing some "racegas" (RACE GAS | Racing Fuel Concentrate) into the tank, since it helps my 749 in the summer. it's just weird how consistent the misfire is, I would think a fuel issue would cause much more erratic behavior? I haven't checked the exhaust or air filters in a while, I'll check them out tonight.

Also I will clarify with my mechanic regarding what was swapped. Although he is closed today, so I'll get that info tomorrow.
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post #6 of 27 (permalink) Old Aug 22nd, 2016, 1:03 pm
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I don't want to come across as an expert on these bikes as I've have mine for something like 4 months - but it has also had an odd "misfire" type issue, though more sporadic than yours from the sound of it. I did many of the things you're doing, mostly with no result. In the end, it seems like the thing that affects it the most is gasoline. If I fill with ethanol-free 91 from one of the stations that offers it, it runs totally fine. If I put a tank of ANYTHING else through it, it misfires for 200-300 miles. I'm wondering if it's not the gas itself, but rather it may be that the gas is affecting something else (i.e. swelling the o-rings in the QD fittings on the tank, etc). Around here, what you get for gas is typically either straight gasoline or 10% ethanol, so not nearly as watered down as E85. If you're using a blend with 10% ethanol, maybe try something pure if you can get it?
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post #7 of 27 (permalink) Old Aug 22nd, 2016, 1:43 pm
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Clogged fuel injector, perhaps.
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post #8 of 27 (permalink) Old Aug 22nd, 2016, 4:26 pm Thread Starter
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@dwizum definitely possible, I'm sure the bikes age and mileage doesn't help. All the gas around here is also at least 10% ethanol, but some stations still keep pure gasoline, I'll see if I can find one of those stations.

@Strega , I thought this might be the issue for a long time, but my mechanic swapped the throttle body assembly, with injectors, from a working bike, and the issue was still present on my bike. I'm going to call him up tomorrow to confirm/get more info. I wish I could do an injector test but considering how inexpensive the whole throttle body assemblies are on eBay I might just snag one of those (and a set of low mileage coils).
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post #9 of 27 (permalink) Old Aug 22nd, 2016, 10:46 pm Thread Starter
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Alright, so apparently the tank is almost empty, yay, I'll get some pure gas to try out. Looked down the intake runners and mufflers, everything looks clear, although the right can (front cylinder) has a lot more soot built up than the left can.

Some history I forgot to add. The bike used to have a nasty issue when rev'd up past 9k RPM and held there for 10-20 seconds, the engine would sometimes seemingly lose power and basically coast, no engine breaking or anything. Any throttle input usually had no effect but rarely the engine would attempt to rev up (with throttle input) sounding extremely bogged down. After a few minutes the engine would return to normal operation (keep in mind it would never actually stall). Eventually I realized this only happened with the high beams on.....and the previous owner had installed an HID kit. My mechanic and I traced the HID harness and realized it was arcing/grounding to the frame. We removed the high beam ballast/harness and the problem appeared to be fixed. This was all happening while the surging/misfire was getting worse and worse. I'm wondering if the arcing/grounding damaged some/one of the sensors or ECU? I know this screams TPS, but we tried another TPS. I'm thinking it's time to just replace most of electronic components (TPS, coils, ECU, EPROM).

Last edited by FORCED-INDUCTN; Aug 22nd, 2016 at 10:52 pm.
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post #10 of 27 (permalink) Old Aug 23rd, 2016, 7:06 am
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Have you tried the whole game of TPS reset, balance the throttle bodies, set idle, and adjust CO? Even if it doesn't fix this problem, it sounds like there's something unbalanced between the cylinders if one is more sooty than the other.

If the problem is still present with another ECU and TB then I dunno if I would bother trying to replace the ECU, EEPROM, or TPS. Coils are cheap so might as well (I got a good used pair on eBay for like $30). Have you tested the air temp sensor and coolant temp sensor? Procedure is in shop manual, takes 5 minutes with a multimeter and might rule those out.

If you do try different gas, I'd do 3 or 4 tanks before coming to any conclusions. After a tank with 10% ethanol, it takes that long for my bike to get back to normal. I really would love to find out exactly what's going on so I can get it to the point where it'll run on normal gas so I can stop hunting out ethanol-free gas. I have found that puregas.org is a huge help, they even have a mobile app that can route you to the nearest station with ethanol-free gas.
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