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916 Starts Then Dies...

Discussion in '748 / 916 / 996 / 998' started by TNR, Apr 19, 2021.

  1. Minimum compression for a non-SP 916 is 113psi (Haynes spec).

    Motor may be a bit tired, but compression is not the issue.

    Cam marks are all lined up as they should be when crank pulley dot aligns with case mark, so I'm ruling that out too.

    Temp or other sensor issue sounds most feasible. Hopefully get time to sort this week- we're in another lockdown and kids are off school so tinkering in the shed is at a bare minimum.
  2. You have triggered a memory, could well be the air temp sensor playing up or equally as likely, the connector itself as it loves to retain moisture and corrosion particularly if rubber boot perished and they often are. upload_2021-5-4_4-20-54.jpeg
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  3. looks like a pressure sensor straight out out of a cinquecento. which has also sparked a memory. it's the same symptoms as a Mrk2 punto, or was it the Grandi? cant mind, but they use the air temp sensor for fuelling rather than the coolant sensor for start up. and they failed regularly but if you gave it a bit of throttle and held it at a fast idle for a mo, it would be fine.
    i believe the two manufacturers used a few of the same sensors around that time, so maybe.
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  4. That's the air pressure sensor.

    Will check it along with temp sensor under headlight.

    I feel like plugging in a mathesis to the diagnostic port next to the ecu would give me a quick answer. Anyone used an OBD adaptor on a P8 bike before?
  5. IAWDiag is the software that you need, though other pieces of software will do the trick, see my post here
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  6. yep, posted at 4.21 am so excuse the predictive text, as per @finm checked and tested many. In the Ducati's case the unit itself hardly ever gave trouble (ime) but if water ingress* around connector happened then would play havoc.

    * quite likely due to connector orientation and position.
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  7. yip, i've changed a few, they dont necessarily register as a fault. usually only if they go open or short curcuit.
    if you can get live data you can compair the coolant and air temp. obviously you would expect the two to be roughly the same if the bike aint been run in several hours.
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  8. I replaced my air temp sensor yonks ago as it fell apart in my hand as I was removing front end when I put my FG43's on. The wires had corroded and snapped if I recall. (was over 15yrrs ago)
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  9. Had a few minutes to tinker so did a sanity check on spark, air, fuel.

    Good spark on both plugs, air filters clear, fuel squirting from both injectors (although fuel pump still not sounding like it's building pressure). Fuel relay clicks after 5s or so.

    Checked air pressure sensor connection as recommended. Looks clean:


    Plug & boot was also spotless. Considering the age of the bike, really not a lot of decay on rubber or anywhere else.

    Checked ecu because why not.

    No corrosion, eprom clean and secure:


    Double (triple) checked timing marks... everything lines up.

    Tried starting.... so close, but no dice once again.

    So on to sensors. I'm happy to pull the temp sensor and test, but would it be less hassle to simply buy a new one?

    Noticed a bit of oil around RPM sensor... is this a reason for concern?

    #49 TNR, May 6, 2021
    Last edited: May 6, 2021
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  10. It’s good to cross all those checks off the list, if you had a spare crank position sensor, that would be another one to try. Can’t really comment on the oil being a problem or a factor here.
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  11. "although fuel pump still not sounding like it's building pressure"

    There is a big clue there
  12. I agree... but 1) fuel is getting to the injectors, and 2) there is pressure in the lines when I disconnect the QDs under the tank.

    Like you mentioned, pressure regulator highly unlikely to fail... what else could it be?

    Here's another vid I took after the checks this morning, including pump prime.

    #52 TNR, May 6, 2021
    Last edited: May 6, 2021
  13. Worth investigating at some point, but most likely not the cause. You're getting sparks, which wouldn't happen if your timing sensor wasn't firing. It *could* be intermittent, but probably unlikely.
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  14. You have a good spark so forget sensors. You are satisfied the timing is correct.
    You get some fuel and it almost starts.
    The only "fault" you found is the fuel pump not sounding right.
    Either the pump is knackered, fuel hose is split or pressure regulator is knackered.
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  15. I've been there. Mine did exactly the same. Fuel hose had a small split in it.
  16. I haven’t read all of the thread as lots of replies but I think I would (carefully) try using easy start or similar just to try and confirm it’s a fuel problem. You don’t have to fully remove tank to do this.
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  17. TNR, it is spinning over fine and the engine sounds fine and normal. The issue I have is the fuel pump sounds very odd and seems to be on for longer than usual, it should make a consistent buzz (no warbling) and start and stop more positively than yours is doing. My gut feeling is the fuel pump is not running properly or there is an issue with the in tank pipes suggested before. Have you replaced the fuel pump and ecu relays under the seat and checked the security of the related fuse connections and the tank power supply plug connections? If not that should have been the first thing you did.
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  18. Hi Denzil,

    We're certainly narrowing it down here.

    Fuel pump is the 26 year old original. In-tank hoses are brand new, along with the filter.

    Fuses have been checked, fuel relays checked but not replaced.

    I will buy a new pump today and update once installed.
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  19. Seems to be down to pump, filter, or lines. Pump would change sound, filter reversed likewise, lines unlikely as they are new unless restricted in some way.Must be close to fire up now! Good luck
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  20. Qd's not reversed? Done that as well.:)
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