Ducati.ms - The Ultimate Ducati Forum banner
  • Hey Everyone! Enter your bike HERE to be a part of this months Bike of the Month Challenge!

1 - 20 of 48 Posts

·
Registered
Joined
·
337 Posts
Discussion Starter · #1 ·
Glad to see by recent posts that I'm not the only one, but I'm having trouble getting a 998 to start after some servicing. Full disclosure below:

Bought the bike in terrible cosmetic shape, but it did start and idle/run. I plan on racing the bike so I began by servicing it to get a baseline. I originally purchased a vertical cam gear holder to assist replacing belts, but I could not get the damn thing to fit at all with the horiz set to TDCC. So I gave up and borrowed the factory tools from a Ducati dealer which I'm more familiar with. Adjusted valve clearances and replaced the belts using the factory cam lock and crank lock tools(I've used these before on 999s, 1098s, MTS1200s etc). Also replaced the plugs with iridiums - set plug gap to .6-.7mm as in service manual.

Turning on key, fuel pump primes (fresh fuel and fuel filter), starter button - engine cranks and cranks but backfires through the intake and doesn't start. Sounds like classic timing issue from my experience. So I reinstall all the factory cam lock tools, lock the crankshaft, verify the mark on the generator is in the correct position within the window. Verify the lay shaft dot is lined up for correct TDCC position of Horiz cyl. All lining up perfectly and seems 100% visually correct. Horizontal camshaft 'T's pointing at slightly 'past' 3 o'lock. Vertical Ts meanwhile, pointing at 4:30 - again, factory tools fit in perfectly.

Check for fuel - I can see fuel visibly spraying from the injectors. So I try some starter fluid into the airbox - nothing. Same issue of cranking and backfiring through intake but nothing more. Remove the plugs to make sure all is well there. I have good spark and even ohm'd out the coils to be sure those were as designed. Read on here that iridiums may be problematic - so I put the plugs that came out of it BACK in. Still strong spark, still backfiring through intake and not starting. So I removed the cam covers to eyeball the camshaft lobes to make sure they looked in the correct position - which they do.

I've rebuilt many engines before, including Ducatis but I've no experience with the 998 in particular. But I'll be damned if this thing doesnt sound like the timing is off. I have a compression tester adapter coming this weekend to verify that I'm actually making good compression. I dont believe any hard parts have ever been changed (camshafts, layshaft etc). I'm quickly running out of ideas. Any guidance is appreciated.
 

·
Registered
Joined
·
337 Posts
Discussion Starter · #4 ·
I did consider the TPS, but man it would be quiet odd/coincidental if it were to just go wacky during servicing while never being touched. I'll make a little pigtail lead and try to verify output this weekend and report back. Thanks gents.
 

·
Registered
Joined
·
337 Posts
Discussion Starter · #6 ·
Reset the TPS by factory procedure. Removed throttles, disconnected linkages and cables, backed off throttle stop screws and set TPS to 150mV while resting closed. Then dialed in the horizontal throttle stop screw until 403mV (figure found in the service manual). Reconnected linkages and cable.

Same issue persists. Backfires and coughs through the intake, but will not start and run. Next step will be compression test to verify camshafts are in the correct position even though i've verified with the locking tools already. My only thought is perhaps someone has replaced the camshafts or gears in the past and the marks no longer line up where they once did.
 

·
Registered
Joined
·
3,978 Posts
Since you had the battery box removed, did you replace the ground for the ECU? It's easy to miss replacing this wire on the ecu bolt...
 

·
Registered
Joined
·
3,980 Posts
Flood the cylinders until she starts, then flog the sh*t out of it for 20 miles. She won't talk back the next time you need her. The older bikes love that sort of stuff.
 

·
Registered
Joined
·
337 Posts
Discussion Starter · #9 ·
The ECU is grounded properly. Turns out the compression tester fitting isn't deep enough to fit down into the cylinder, so I'll to make an adapter of some sort.

In the mean time I removed and cleaned the fuel injectors with brake cleaner and compressed air. I reinstalled everything but the fuel tank and poured a cap full of fuel down into the throttles and tried again to fire it up (because again, I have good spark). Same issue persists. Bike puffs and coughs. Sometimes through the intake, small fireball out of the exhaust but not even close to starting and running.

This damn thing has to have been modified before my getting it making the timing tools unusable.

Just to recap: Got good spark (ruling out plugs, coils, wires, relays, grounds etc). I can see fuel squirting from the injectors (ruling out injector relays, fuel pump, filter, hoses or the injectors).

One last thought - I came across a couple of threads of people reporting their 998 not starting and their tachometer not working properly. I do know that the tachometer does not 'bounce' or move when I try to start the bike. Should this be moving before the engine starts? I'm wondering if this issue could be tied in here somewhere.
 

·
Senior Narcissista
Joined
·
5,737 Posts
If its about to start but doesnt catch on it may be worth checking the starter sprag is letting go as it should, if it is binding both ways itll render that symptom.
To check turn engine over in the running direction and see it doesnt have that grinding noise from the starter gears it has turned backwards.
Just one idea that is free to check :)
 

·
Registered
Joined
·
337 Posts
Discussion Starter · #11 ·
If its about to start but doesnt catch on it may be worth checking the starter sprag is letting go as it should, if it is binding both ways itll render that symptom.
To check turn engine over in the running direction and see it doesnt have that grinding noise from the starter gears it has turned backwards.
Just one idea that is free to check :)
It doesnt sound to me like it's about to fire off and run. I've had cars out of time (installing flywheels in the wrong position) and it sounds exactly like that. You can hear some compression, a puff or two, coughs from the intake, the occasional puff from the exhaust, but that's it.

Turning the engine over by hand it feels and sounds fine rotating in the correct direction. Nice and smooth. I don't suspect the sprag is causing any trouble at all.

Any other insight lol?
 

·
Registered
Joined
·
337 Posts
Discussion Starter · #12 ·
I've noticed another thread or two during searching that had similar issues to mine that resulted in the ECU being replaced before the bike would run. If the injectors are pulsing, and the coils are firing and I have compression, is there any way the ECU could keep the engine from running?
 

·
Registered
Joined
·
337 Posts
Discussion Starter · #14 ·
Front cylinder is in fact at TDC when the layshaft dot is aligned with the case 'line' as well as the flywheel mark seen through the generator cover window.

Yes the start/stop switch is at 'run'. I've flicked that thing back and forth several times to see if there's any difference - none. I was honestly SHOCKED to see if not even run for a second or two with fuel poured down into the throttle bodies knowing I have good spark. I'm at a loss here.
 

·
Registered
Joined
·
8 Posts
sounds like something I've tried........................... :)
Have you accidentally swapped the connectors on the ignition coils and/or on the injection nozzles ?
 

·
Registered
Joined
·
337 Posts
Discussion Starter · #18 ·
sounds like something I've tried........................... :)
Have you accidentally swapped the connectors on the ignition coils and/or on the injection nozzles ?
I haven't swapped the connectors on the ignition coils, but would this even matter? It appears the coils fire whenever either piston is at TDC whether it is under compression or exhaust stroke. Also, the injector nozzles are labeled O and V, so I've kept them in that orientation.

I'll try to get a clip tonight of what is happening as proof I'm not losing my mind. Damn thing sounds EXACTLY like it's timed 180* out.
 
1 - 20 of 48 Posts
Top