ST4s wouldn't rev above 4k

[ridelaleonessarossa]

Hello all, I haven't posted here before, but I had found some great information spread throughout these forums when I was troubleshooting my bike - so I thought I would share what I had learned when I actually fixed mine.

... 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 rpms.

I didn't want to trailer a "new" bike for repair in Raliegh, and I was pretty good "feeling" that it had something to do with something electronic, given the fact that it went for 1000 miles perfect, then started farting around after the deluge. But it didn't stop after I garage and dried the bike so... huh.

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 water-proofed housing.

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.

Except, THIS computer sounds like a freakin lion.

Well, I hope someone finds this useful for their backfire experiments!

[Essing]

I had the same exact symptom with my 2004, would not rev over 4k. It could be many things, also check:

Cracked fuel lines inside the fuel tank.
Bad gas
Clogged fuel filter
or ..... what was wrong with mine......
cable not completely clicked into the ECU.

Clicked it in and locked it, back to a "bat out of hell".

-Bill

[scott]

Mine hasn't done that but WELCOME to Ducati.ms

[Fariborz]

Michael,

That was very informative. Thanks for sharing.

-Fariborz

[Desmo_Demon]

My 748 did the same thing back in October of last year. I cleaned all the connectors in the wiring harness, replaced the fuel filter, checked the outputs of the TPS and air temp and pressure sensors. I have no idea what it was, but it's run great ever since. I suspect water/corrosion in a connector, but I really don't have any idea.

[grimah1w]

Great post; thanks for sharing the info.

[ridelaleonessarossa]

Nice to know other people ran up on this problem too. It's interesting that the everyone's responses so far indicate problems being traced to connectors and wiring! I guess my next project will be figure out some way to better weatherproof these "automotive grade" connections.

[dyno]

Get yourself some Dielectric Waterproof Grease.
Unplug each connector, apply the grease and connect again.
It's time consuming but worth it. I just completed the same exercise on my 916.

[ridelaleonessarossa]

Originally Posted by dyno

Get yourself some Dielectric Waterproof Grease.
Unplug each connector, apply the grease and connect again.
It's time consuming but worth it. I just completed the same exercise on my 916.

Great advice.

Do you have any idea on what to use to replace the rubber gasket/coverings on the exterior of the connectors - or would you just liberally apply the grease on the exterior too? I was thinking heat shrink tape, or some marine type caulk.

[guido]

Hello
I had the same thing occur right after washing my bike. I opened and DiElectric greased all of the connections I could reach, replaced the coils and plug wires (and the plugs, since I was there..) and presto! I don't know which of the above did the trick, but it was almost certainly water in a connection....
Any idea what your bad-actor connection went to?