So, my 1990 851 has an issue where it will start and idle fine, but when it revs to 5500-6000 or so it will sort of bounce back and never get above it, like it momentarily cuts out. If you keep the throttle open it will bounce between 5-6k rev up, cut off, rev up, cut off, repeat ad nauseum. It's a pretty hard cut off. I've replaced the wiring to the pump and tried it bypassing the fuel filter so I'm pretty certain it's not that. It does it in gear, neutral, uphill, downhill, etc.
It's like it's trying to change something - ignition, fuel, ? - to another rate for higher revolutions or load and can't do it.
My basic mechanical skillz are okay but electrical diagnosis is voodoo. I can connect a voltmeter and read stuff but once it gets into things with acronyms I'm a little lost.
For those not familiar, the 851 is 4v, fuel injected.
Any ideas? Thanks!
The very best place to ask is here:
http://www.ducati851and888.com/index.php (http://www.ducati851and888.com/index.php)
Tremendous amount of knowledge there!
any recent service or work done?
Quote from: Raux on March 07, 2011, 10:49:08 AM
any recent service or work done?
No. Well, the last work I had done was to the fuel level sending unit at Desmotosport, and that part failed again, so I replaced it. I had thought the rev thing might be an issue with the sending unit - like starting to go before it crapped out entirely - but no joy.
It needs to go in for valve service, and if I can't figure this out I'll limp it in and pay someone to do it, but it's pissed me off some and I want to conquer it. Particularly because I let it sit some so I could do it.
I forgot to mention, I have the service manual so tracing stuff is not too much trouble, but as far as why to check any particular thing it's pretty worthless.
sounds like fueling issues
not enough fuel at higher revs?
That was my original thought too. Or my original hope. So that's why I started there. I suppose it could be in the injectors but it's such a hard cut-off... Fuel pump draws power from the relay and the coil, and I know the relay's powering it. My thought was if the coil-pump connection was kaput then it was more just starve itself and not rev well at all, but it does - until that hard cut. Also, it will backfire sometimes after that cut which leads me to believe - hopefully correctly - that it's getting enough fuel but spark is being cut. ???
well hopefully one of the smart guys will chime in here shortly
Brad will come f sure....
Right on. The more and smarter the merrier!
Tonight I'll pull the TPS connector and give that a cleaning, I suppose.
It sounds like an ecu issue to me.
if the voltage regulator is solid mounted, rubber mount it.
if it's rubber mounted, solid mount it.
OK. Why?
I checked the phase sensor and crank position and both were clean, no debris. I didn't get voltages since it was midnight and people frown on running the bike then. Not me, other people.
My bet is on a perforated fuel line inside the tank.
Quote from: brad black on March 07, 2011, 06:20:41 PM
if the voltage regulator is solid mounted, rubber mount it.
if it's rubber mounted, solid mount it.
I think that's a translation for "Not sure mate, but something's rooted."
Quote from: Speeddog on March 08, 2011, 02:10:50 PM
My bet is on a perforated fuel line inside the tank.
Just had all the lines out and they looked good.
Quote
I think that's a translation for "Not sure mate, but something's rooted."
[laugh]
Just for fun, open the cap and turn the key on, see if there's fuel flying around inside the tank when the pump's running.
Brad may have been serious for all I know....
Quote from: Speeddog on March 08, 2011, 02:21:04 PM
Just for fun, open the cap and turn the key on, see if there's fuel flying around inside the tank when the pump's running.
Brad may have been serious for all I know....
Sure, good call.
Also it seems to be rev related and not load - I'd expect a fuel system problem like that to be load related?
i was serious.
on at least 2 851 that i've seen with a complete shut down symptom the cause has been a voltage spike apparantly caused by the regulator. altho these, like all over vibration issues i've seen with 4v bikes, happen at 7,500 rpm. loose engine mounts may bring it lower, as i guess could cracks in the cases between the mains and timing shaft, but that's an extreme issue.
they shut down, the ecu turns itself off to protect itself from the spike, then turns itself back on, gets its shit together and starts doing its thing again. and because the revs have dropped due to no power it'll come back, hard if the throttle is still open. probably shuts down for a second or two, feels like an eternity. then it'll charge back to 7,500 and shut down again.
originally the regs were mounted with well nuts holding them to the frame. there was a service bulletin saying to solid mount them (reg earth wire issue maybe? i forget) and on a very small number of bikes this miss would suddenly appear at some time (long time) in the future.
so you'd replace the nuts and washer with well nuts again.
dunno if it's your problem. personally i'd certainly check it, but that's up to you.
Thanks, I appreciate that. This isn't that long, it's about 1/4 sec, only enough time for the revs to drop about 500-1000 rpms before it picks back up. Since I'll be home during the daytime I'll pull a couple other things apart, clean, and reassemble to try today.
Does anyone have any idea what the diagnostic tool is they refer to in the manual that reads the flashes? It doesn't look like the Mathesis. That's just a curiosity thing.
could be fuel stravation caused by old fuel filter it happens often on Ducatis with EFI
I tried bypassing the filter, no change.
Thanks a lot (again), Brad! [thumbsup] :)
Your tip cured a 916 SPS which cuttted hard at 3000 RPM.
So after I punted and took it in for service anyhow and had them give it a look, I've got it back.
The verdict: who knows, sort of. It went away after they did valves and belts and some other nonsense, which included replacing a wire that was in poor shape coming off the stator, which was all corroded and cracked. Since it wasn't intermittent before and has now disappeared entirely, I think it's quite likely it was related to a voltage drop due to that wire. At least, for lack of anything else relevant being done.
Quote from: B.Rock on June 13, 2011, 12:14:23 PM
So after I punted and took it in for service anyhow and had them give it a look, I've got it back.
The verdict: who knows, sort of. It went away after they did valves and belts and some other nonsense, which included replacing a wire that was in poor shape coming off the stator, which was all corroded and cracked. Since it wasn't intermittent before and has now disappeared entirely, I think it's quite likely it was related to a voltage drop due to that wire. At least, for lack of anything else relevant being done.
It came back and left me stranded. Fuel pump totally failed. [roll]