916 sputtering, stalling, coughing... Being a pain - Ducati.ms

JEC · Jul 1st, 2012, 11:39 am

I've been hunting down an intermittent problem with my 916 that just seems to be getting worse despite my repairs. Now it's gone from intermittent to fairly consisent once the bike gets up to temperature.

Cold start it seems fine. Before it hit 160f it runs normally. Then throttle response goes wooly, then the motor starts to sputter and bog. At idle it runs poorly, not quite "on one cylinder" but lower and lumpier than usual. It will stall easily and it is coughing through the intake a lot. Enough that you can smell the fuel mix from under the tank. When you accelerate it is lacking power and surges badly. Steady throttle has it hunting all over the place.

So far I've replaced:
The fuel pump relays
The coolant temperature sensor
The fuel filter
The fuel lines
The quick disconnect o-rings
The spark plugs
The spark plug wires (Magnecor)
The battery
The battery cables (Motolectric kit)

I checked for intake leaks but none are apparent. It seems to be running extremely rich in any case.

My next line of thought:
Crank position sensor (I checked the gap about 3000 miles ago and it was right in spec)
ECU
EPROM

Any suggestions?

JEC · Jul 1st, 2012, 11:50 am

Oh, and I run a permanent voltmeter and the voltages are all within spec so it isn't a charging/RR issue.

Namor · Jul 1st, 2012, 2:20 pm

What is voltage at;

battery off
ignition on at battery
the number that drops when you start the bike (at battery)
running at battery
running at 2k and 6k rpm

Is one header not heating up at all or as quickly as the other?
Don't forget to check the atmospheric whatever sensor on the top of the coolant reservoir.

How did this happen? Over night, after modifications, or slowly bad until it got to where it is now?

black77s · Jul 1st, 2012, 2:26 pm

back when my 749 had similiar issues. it was resolved with valve work

JEC · Jul 1st, 2012, 2:56 pm

Battery was replaced at the start of the season:

Battery off - 12.7-12.8 (goes as low as 12.6 if I leave it a few days. I put it on a trickle charger which brings it up to 13, which drops to 12.8 in few hours after removing the charger. It will charge up to 12.8-12.9 after riding for a bit)

Idle - 12.4-12.5

Drop on start - 10.5 minimum

2k up - maxes at around 14-14.1

RR and alternator wires are in good shape, no overheating, no corrosion at the plug.

I checked the spark plugs after a ride around the block when it was acting up. The front cylinder is running lean, the rear is close to perfect mix. This is unusual because I run a rich mixture and usually have black-brown plugs, especially after a ride around town.

I pulled the timing sensor to check for debris. Aside from a little grime it looked ok. I plan on checking the resistance tomorrow once the bike cools down (spec is checked at room temperature).

ECU and EPROM look fine. EPROM is seated properly, and there is no evidence of moisture entry. All connectors are greased and free of corrosion.

I went over every intake bolt and union to make sure there were no leaks. Nothing was obviously loose and the rubber is in good condition and seated properly. I did a WD40 test with the engine running and couldn't find any evidence of a leak around the throttle bodies.

Valves were done 3000 miles ago, I replaced a couple of rockers and MBP collets were installed at the same time. The TBs and TPS were balanced during that service. It's run perfectly up until now.

The problem began on my first long ride this season. I went 150 miles with no issues. Then it started backfiring and losing power. I checked for leaks or obvious issues, couldn't find any, and after another 15 or 20 miles the problem disappeared. Thinking it was a fuel issue, I changed the filter and lines. I had a problem with the quick disconnect o-rings restricting flow as well so I changed those. It did nothing to help.

I took it for a test ride and it died after I bumped then coolant union on the left side. I played with it and it started again. I checked the voltage at the coolant temperature sensor and it was ok, but I replaced the sensor as a precaution as well as the fuel pump relays. The union mount was loose so I tightened it. Didn't help. Since then wiggling the coolant union /wiring doesn't seem to change anything.

Since then it's been getting more frequent. Now it does it any time I ride it. This morning it was at its worst, it started within a mile of home and was almost totally unrideable.

Quote:

Originally Posted by Namor

What is voltage at;

battery off
ignition on at battery
the number that drops when you start the bike (at battery)
running at battery
running at 2k and 6k rpm

Is one header not heating up at all or as quickly as the other?
Don't forget to check the atmospheric whatever sensor on the top of the coolant reservoir.

How did this happen? Over night, after modifications, or slowly bad until it got to where it is now?

cyclops · Jul 1st, 2012, 3:34 pm

Have you checked the TPS, some times they play up a bit with age.

JEC · Jul 1st, 2012, 4:09 pm

I adjusted the TPS 3K ago. I'll do a voltage check on it next to see if it is acting up.

So we have the following that have yet to be checked, in order of likelyhood -
Bad crank position sensor
Bad atmospheric sensor
Bad EPROM
Bad ECU
Bad TPS
Loss of compression due to valves

Any other ideas? This is really stumping me and it's driving me crazy. I've had issues similar to this before that were relatively easy to diagnose and fix (usually a burned out sensor or a bad connection somewhere).

Namor · Jul 1st, 2012, 5:01 pm

So your charging system is fine.

I've messed with the TPS enough to experience what you have, but the bike had a series of problems back then and I think the TPS was a contributor and not the main cause.

Do you have a spare eprom? I have a 916 BP you can have for $10 if you want to go that route as a test.

Just check the valves, but I don't think that's it.

Make sure the rubber on the intakes haven't been compromised by over tightening on the TBs.

Are your fuel lines routes in such a way that they could be causing vapor lock? Not likely.

Coils, this is where i would go next. Check for spark, cracking, and correct voltage.

Are the ports for the canister on the TBs possibly not plugged? Hence lean on horizontal.

How long do you think it will be before you go insane?

JEC · Jul 1st, 2012, 5:23 pm

I have a stock EPROM somewhere. Just need to locate it. I find it unlikely though... The ECU going bad I could understand, it happens on occasion.

I checked the intakes thoroughly. I had an intake leak a few years ago due to a re-used crush gasket (lesson learned). It had similar symptoms albeit without the loss of power, it would stumble, backfire, and afterfire.

All the plugs and bungs are good and tight, as are the intake runners, and the rubber. A quick test is to spray WD40 at the various joints while the engine is running and listen for a change in rpm.

Vapor lock was my first suspect. I replaced the internal and external hoses on the tank. I check them everytime I move the tank (I leave two seperate lines and have them coming out the side of the bike so I can blow through them).

Coils are another possibility.

I'm going to do voltage tests on the CPS, TPS, atmospheric sensor, and do a spark strength test. But not today. I've had enough dead ends for one day.

It's been doing this since mid May. I have no gotten a decent ride in since that first one when it acted up. I am going crazy just by virtue of not being able to use it!

Vorais · Jul 1st, 2012, 5:25 pm

I'm currently experiencing same issues with my 748. I'm in a little worse position as I recently purchased the bike and don't know the history of it. I have it in capable hands here with a local shop in Milpitas and hopefully the can find my issue. (They are also doing a full service, fuel filter, fuel pump, coolant tank, replacing any bad rockers etc.) If they figure out mine I'll report back what it was (maybe my root cause is similar to yours)

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