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3,997 Posts
Discussion Starter · #1 ·
At work and don't have time to search the forum.

996. Runs great, starts fine, idles fine. Coming to a stop it dies. It can idle all day once started. If hold the revs at 5-6k then let the throttle go it won't die. Dies only after coming to a stop.

Recent top end rebuild.

TPS set before build.
Idle is at 14k
Throttle cable is correctly tight
TBs are secure and tight.
Intake manifolds are secure and tight with excellent condition gaskets
New style airbox.
New Battery.
Charging at 12.9v at idle
Good seals on air runners to airbox

Any suggestions?
 

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Blip the throttle as you're downshifting...blip 1 or 2 times as you're stopping...

14K idle? I think you're violating the rev limiter.

Also, if it's 1.4Krpm idle, battery voltage sounds low to me. What's it settle out to when you hold RPM at 2500?
 

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3,997 Posts
Discussion Starter · #3 · (Edited)
What's it settle out to when you hold RPM at 2500?
13.15 volts. I know that is low and am about to jump to a new stator. However, I want the stalling issue sorted first. And it didn't stall before the rebuild.

Yes 1.4k rpm at idle

(10 minutes later) A/C current on yellow stator wires is 10.4 at idle down to 9.4 per wire until it jumps back to 10.8 on throttle.

And, unless it's since I bumped up compression (new pistons and cylinders and squish) I don't know why it would start stalling. Again, I know I have a charging issue. I want the stalling cured first.

(edit + 30 minutes) TPS remains spot on. Perhaps the butterflies need adjusting after pinston/cylinder swap, but I doubt it.

(edit + 1 hour and ride home) Dies after a drop from 4k rpm and up. Blip will keep the engine alive but it's annoying to do around town.
 

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Old Wizard
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3,006 Posts
Check for the clutch dragging. Put it in gear running on a service stand, pull in the lever and see if the rear wheel stops turning. Does it have a lightweight flywheel?
 

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Discussion Starter · #5 ·
Light flywheel, and clutch does drag in 1st and second but the wheel is very easily stopped with my hand and idle remains the same with the wheel stopped and clutch engaged. Plates are still semi-hot from ride.
 

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Discussion Starter · #6 ·
It reminds me of a vacuum leak. Noticed also, after more time on the bike, that idle will start at 1.8krpm sometimes while others at 12-14krpm. If it does fluctuate at idle, and it doesn't all the time it eventually stabilizes at 14k rpm.

Sometimes after blips of the throttle it will bump down to 1.2k rpm for a bit until I bring it up . And, I may be being overly sensitive to it, but since I put the new pistons and cylinders on the engine heads up faster. Running water and water wetter.

I have 2 approaches to fixing this and possibly three. Does anyone have any suggestions?
 

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How did you make sure the timing belts went back on the way they should?
Do you know what the CO values are? i.e. is the bike running rich or lean?
 

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Discussion Starter · #9 ·
I'm not running rich, or "rich" for a Desmo. The plugs are exactly what you would like to see, but I don't have a CO reader to check it. It was fine before the rebuild.

Synching/balaning TBs, was done a few months ago and set correctly. I don't know why I would have to resync them after and R&R but that's what I am going to check this afternoon.

Timing belts. Use white-out on belts and and teeth on cams/crank pulley. They are exactly where they were before the removal.

I am down to vacuum and TB synching. I'll have the shop to myself in a few hours and will go from there.
 

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Discussion Starter · #10 ·
No vacuum leaks. Throttle bodies were slightly out of syn. Synchronizing them didn't make much of a difference and here is how things are.

The bike will die and just drop off if I let the throttle off. However, as I have said before, up and down between 3k throttle it won't die.

Idle remains erratic and wanders from 1.1k to 2k as it sits.

Now I have noticed that sometime when I drop the rpms off from 6k and up the idle will float from 2.6k-2k (like it's running very rich) and stay at 2.2k. Also, it will sometimes float down to the low 2k range, float, then either die, or nearly die and hang on at 1k rpm.

The bike rips without problem as long as I am riding.
 

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Were the valves checked for leakage ?
Guides checked ?

The higher comp piston could be making a leaky valve issue noticably worse than when you had the lower oem ones in.

Just a thought.

When I had my corse I had a motec ecu. With that I could see if I was running rich or lean. When it was rich it displayed many of the symptoms you descibe.
 

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Discussion Starter · #12 · (Edited)
I cleaned them, the valves, and with the heads upside down the the dome filled with brake clean they either have very minimal loss off break clean or the break clean evaporated over the 30 minute period. So valves and seats were "ok" by my standards. And the pistons weren't HC. Stock.

I just got in from a longer ride without having to stop. There is a noticeable improvement in throttle response over 6.5k rpm. I am happy with the engine for now, minus the rpm/stalling issue and the fact that it gets hot faster, as in at 210 within 1.5 miles at 40mph.

Didn't have my glasses on, for seldom do I need them, stator wires are putting out 112VAC a 2k rpm. Cleaned the connection to the RR which just happened to have oil from a very very slight leak at the oil cooler hose fitting. Stator OHLMs out at 1.2 across each arm. Bike idles at 13.3v and gets over 13.5v after 4k rpm. I hear by declare my issue to not be from the following; TPS, synced flies, charging, battery, fuel, tires, oil, grips, mirrors, carbon bits, and valve caps.

And KiwiEd, after 4 hours of your post, and finally reading the last sentence, I have a ray of hope. (I have lots but have been saving this special one)
 

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3,997 Posts
Discussion Starter · #13 ·
leaned the bike out. problem is worse. Now if I hold throttle at 4-5k rpm the rpm will wander +/- 800rpm. Nice thing is the engine runs rough now and feeling like it is missing.

I am inclined to think that a coil is expiring, I have a bad plug, and or plug wire.
 

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Discussion Starter · #14 ·
New wires. Plugs check out. Atmospheric pressure sensor is good. Runs very poorly when I lean it out. Runs best at full rich.

I'll post a video later just so you guys whom might have the answer will have something to look at.

2 questions? Can a bad temperature sender for the ECU cause these issues? How do they go when the timing sensor fails?
 

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Old Wizard
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2 questions? Can a bad temperature sender for the ECU cause these issues? How do they go when the timing sensor fails?
The atmospheric temperature sensor voltage level tells the computer how much to modify the fuel map injector durations for a given air temperature. When you take a ride on a hot day, the air is thinner and consequently will cause an engine (that has its air/fuel mixture set correctly for a nominal 68°F day) to run too rich.

To avoid this mixture variation, Ducati fuel injection systems have been designed with air temperature sensors that tells the ECU how much fuel to deliver for a given air temperature.
If the air is colder than a nominal 68°F, the ECU adds fuel. If it's hotter than 68°, it reduces fuel. The sensor's resistance increases with air temperature, 30 K-ohms at −4°F, rising to 370 K-ohms at 168°F

When this sensor fails, you’ll get an open circuit (infinite resistance). To avoid letting the computer think that the day is very hot and delivering an overly lean fuel mixture at normal operating temperatures that could damage an engine, the computer is programmed to default to the preset ambient setting if it sees an open circuit. A bad electrical connection between the sensor and the computer can also cause this to happen.

In other words, if the sensor fails, you’ll run too lean on cool days and too rich on hot days. In both cases throttle response and power will suffer.


If the timing sensor fails, the ECU doesn't receive a crank rotation signal so it thinks the engine has stopped running and shuts off the fuel pump for safety reasons. You don't want fuel being pumped after a crash.
 

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Discussion Starter · #16 ·
Thanks Shazaam. I am guessing I can rule out the rpm sensor. For temp sensor I meant engine temp sensor next to the thermostat. But, I don't recall if the temp sensor, not atmospheric, sends data to the ECU. Is or is it not on a separate circuit, a circuit only for the temp gauge?

I won't have a wiring diagram until I get home.

Can't be the atmospheric sensor for the reason I have stated and because it's 45 degrees out today and on the previous days when the bike ran exactly the same, the temperature was in the 90"s.
 

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Old Wizard
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I don't recall if the temp sensor, not atmospheric, sends data to the ECU. Is or is it not on a separate circuit, a circuit only for the temp gauge?
The coolant temperature sensor (thermocouple) monitors the engine coolant temperature so the computer can supply additional fuel while the engine is warming-up and retard ignition timing if the engine gets too hot.

Engines need more fuel when for a cold start as there is no heat in the ports and chambers to keep the fuel atomized as vapor, so it condenses. Fuel as a liquid burns very badly in the combustion chamber, so throwing more at it ensures enough stays as vapor for some sort of combustion. Injected engines get a very nice fuel spray from the injectors and this is why injected engines behave well when cold.
 

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Discussion Starter · #18 · (Edited)
See the video. Watch the idle. I do not manipulate the throttle once the rpms drop off from the higher revs. Upon start up notice I am around 1.8k but at the end of the video I am at 1.4k where I have set it.

Most importantly, notice the float around 2.4-2k rpms. This is especially obvious on the last deceleration where it floats at 2.4k for a while before it drops down. Lastly, and not seen in the video, the engine usually stalls out immediately after the float.

996 Idle issue - YouTube

(hours later) I hit 210 on the temp after fiddling with things at idle. Fan kicks on and it goes to 200. I have to guess, on top of my running issue, I have either a bad thermostat and or temp sensor. I am at the end of the line on this bike. Jaguars are less finicky. I am thinking 675.
 

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A wandering and unstable idle like that looks like a weak mixture/air leak to me. Given you have had the TBs off are you sure they are seated well and all sealing plugs etc are in place and tight?

Keith
 

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I read through and may have missed it but,
What is the CO level at?
What has the trim been set to?
How far out from closed are the air screws on the throttle bodies?

I have seen this before, just want to get some information to see which direction to go.
 
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