ST4s wouldn't rev above 4k
|Extract of an issue that was posted on Ducati.ms by a ST4s owner:
Join Date: Jun 2008
Location: Wilmington, NC, USA
Posts: 1 ST4s wouldn't rev above 4k
... I just bought a 2002 ST4s, in Key Largo, Florida, and drove it back
up here to North Carolina over last weekend. An absolutely great trip,
1040 miles, and the bike was joy to ride - even on Saturday, going from
Key West to Savannah. The ONLY hiccup I hit was that driving back into
town on Sunday night, I hit a tremendous thunder storm complete with
30mph gusts, unreal rain, and lightning all around. I pulled into town
and stopped at my office rather than continue on through the storm the
additional 20 minutes to my house, and when I got back on the bike - it
would not rev over 4000rpm. Instead, it would rev towards it, then pop
and backfire, and do this over and over. Even stranger, once I got it
idling, and the bike warmed up, it would backfire at lower and lower
Long story short, after about 3 days of messing with it in my garage, I
was getting ready to pull the fuel injectors to see if they were fouled,
and in the process of tracing wires I found one little connection that
was zip-tied to the frame where whoever did the work had stretched the
heck out of rubber connection, cracking it, and turning that one little
inconspicuous connection into a water-filled pouch rather than a
What was it? I'm not totally sure. It was zip tied right above the
battery. It was a three prong male-female connection between a wire
coming off what looked to be the bottom left side of the bottom cylinder
and a wire coming off what looked to be an exhaust feed out from the
that same cylinder. This was the cylinder that was backfiring, I'm sure,
because not only did I take off the air filter to watch it popping cute
little flames back up the intake towards the fuel tank, but it had
toasted a nice little brown spot on the air filter above it. (yeah...
hmm...). So I opened up the connection, stripped off the bad covering,
dried it out, and poof, the bike is back running perfectly. I assume it
was a wire connecting a fuel sensor to an air sensor, and once wet,
could not transmit the changing needs of higher revs.
The reason I post this is that there are ALOT of posts around the web
about these 996 engines and ST engines backfiring, and Ducati's in
general, and most of them seem to focus on the fuel / air and computer
portion of the problem. After discovering that my problem was stupid
simple, but REALLY easy to overlook, I felt compelled to let you know of
all the other relatively expensive things that people were diagnosing
these same symptoms as.
Here's a short list:
The Duc Service Person in Raliegh suggested:
1) Water in the spark plug connections, unplug them let them dry...
(didn't work for me, and were completely dry, skipped replacing them)
The Dobeck Performance 1-800 service guy said:
2) it was pretty unlikely that their TFI 1047 fuel injector controller
would be causing this issue. (because it only adds gas / and because the
settings were right for 1000 miles before that / and the controller
didn't get wet because I checked it and it was way up under the seat.)
But if it had been messing it up, then I could troubleshoot it by
unplugging the power cord to the TFI from the battery, and the bike
would run stock settings to the fuel injectors. (I didn't try this
because his discussion of the fuel injectors is what led me to check the
wires between the injection components and the computer stuff - which is
when I discovered the wet one).
3) he also suggested that it sounded like it could be a "limp home" mode
to the CPU, that some sensor had gone and the bike was protecting itself
- but I have yet to find anything on the various forums about a Ducati
limp home mode, plus there was no check engine light.
Other things that came from the forums and the web:
4) it could have been fouled / bad injectors - unlikely, I thought,
since it had been working okay before, but worth checking...
5) an intake leak messing up the fuel air mix, which from reading about
it should have caused backfires - but not the same way I was having them
(continuous, crazy, at 4000rpm)
5) the fuel / air mix could have too rich and needed to be adjusted down
- although this would have caused backfiring with sudden stopping of
acceleration, not like mine, plus I had this other TFI thing that had
been adjusting this mix for 1000miles.
6) I could have crazy carbon buildup or had bent valves and that was why
it was backfiring back through the air intake too. (Honestly, I think
some people are out there on the forums trying to give the scariest
advice possible to freak people out. And I didn't think that rain could
cause bent valves.)
7) It could have been a broken timing belt - which I rolled my eyes and
thought I remembered that the dealer in Florida had just adjusted the
timing belt - which if broken might lead to bent valves??? OH NO!
8) The same goes for the possibility of a cracked portion of the exhaust
system, equally scary since there are carbon fiber arrows mounted on it,
but equally implausible since why would the rain had changed it?
As you can tell, this thing totally blew my mind. Once I saw that soaked
connection, I was so relieved that it was something simple. It made me
think of the old days of computers and Windows 95, where you turn it
off, unplug EVERYTHING, check every connection, plug it back in, press
the power button and it magically works again.
--Original post on Ducati.ms link from here: