[Beerco]

New to the forum but not Ducatis! I bought my first Duc in 94 - Monster just the second year they imported it! Haven't owned any motorcycles since 1999 though and picked up a 1999 ST2 this summer with about 14k miles on the clock. Wifey and I are loving the bike with the exception of the throttle.

So, the issue I'm having is that between about 3500 and 4000rpm, the motor runs very poorly, stumbles, sometimes backfires if you close the throttle in that RPM range and basically makes it pretty tough to ride. The worst is it happens basically "right where you want to be" throttle wise when just tooling around. This kind of points to possibly a bad TPS.

Generally speaking, the bike runs better when cold than when warm and definitely runs better when ambient air is cold too.

I wanted to take it to the dealer so I wouldn't have to deal with it (Ducati Detroit) but I suspect they just don't like working on old bikes as they were pretty snobby and said it would take 6 hours @ $140 just to remove the bodywork and get to the throttle bodies....and there ain't nothin' that takes 6 hours for a pro to get to on any bike!

From advice I've gotten from other sources, it sounds like my bike could need a TPS reset. Dealer did say that they have seen TPSs go bad in the spot where common riding is done, perhaps wearing away some of the carbon or whatever it is they use in the pots in the TPS. I've also read that coolant temp sensors can go bad and may present in a similar fashion.

I've read the BikeBoy non-linear TPS adjustment article and that seems a bit complicated for me as I haven't wrenched on a bike in years and don't own a gas analyzer for the CO reading. I can wrench just fine - raced and rebuilt motors on FZR400, RS125 (man I miss that bike) for years - but, back then only a few Ducs were injected so we all knew carburetors.

So, I'm wondering if anyone else might have any advice on how to approach this and get it fixed for less money than I spent on the bike!

I already purchased a new non-linear TPS. My plan was to simply read and record the idle voltage on the current TPS, replace it with new and set it to the 460mV as spec'd by BikeBoy. If that runs poorly, I'd re-set the voltage to what I read earlier.

Would also be pretty simple to replace the coolant temp sensor at that time too. Went for a ride today (45º ambient) and when coolant temp was below about 160º, ran almost right. Once coolant gets above about 180º it starts stumbling pretty badly but not nearly as bad as when ambient is higher. Went for a ride Monday when ambient was about 70º and it was borderline unridable between 3500 and 4k - had to really goose it to get it past 4k to run right.

Any thoughts on if this is a good approach or advice on how to tackle this?

Thanks!

 

[ducvet]

I would check around your area to find a independent shop with ducati experience. Check around the racers in your area they will know who knows how to make them run right. Doug Lofgren is out there somewhere so try and find him if he will not do it he may know who can for you. You have a early TPS and it is adjustable you might start by measuring yours before removing it if it does not have a dead spot changing it will not help. Adjusting it very well may help but let me also ask this...

When were the valves adjusted last?
Timing belts changed last?
Fuel injection set up last?
Yes, when was it last tuned up?

chasing for defective parts when you need a tune does not help, if you like the bike start with the basics because at 14,000miles the bike is barely broken in and to get a good life you should start by doing maintenance. If afterwards you still have the issue then start with the trouble shooting.

All stock or slip on exhaust?
open or closed airbox?
stock or aftermarket chip in the ecu?

The area you mention could be tps lean spot for sure but make sure the other things that also may cause it are right first.

Oh and yes 6 hours for that bodywork means they do not know that bike. simply remove the mirrors,trim panels, upper fairing and both sides before bringing it in. That should save 1/2-1 hour labor and they can still run the bike to do what they need to do. If they think that bodywork will take 6 hours then I would be scared to know how long they think it takes to tune it.

 

[Beerco]

Thanks for the advice! Here's some more info:

Valve Adj - prior owner (but not original owner) said last year but unknown. I'll be checking them over the winter.
Belts - replaced this year by prior owner
Tuneup/injection - unknown....probably a while!
Stock ECU, Exhaust and Airbox. Seal is still on the ECU so I could play with the adjustment screw as well.

I took the 6-hour comment to mean that they didn't want to work on it and wanted to scare me away with price. I looked up Doug and sent him a note asking if he could recommend someone around here.

 

[ducvet]

If the bike has had mostly shade tree tune ups the injection has probably never been set up properly, get everything else done and take it in for just that. of course it is upon you to make sure the foundation is correct before they adjust the injection to what you bring them ie: do a good job.

All stock they ran fine but that was pre ethanol so now with some time it may simply be lean and the injection setup may fix that, if not a chip or some chip tuning may help Doug will get you in the right direction.

 

[Beerco]

Thanks, ducvet.

In case I can't find someone to help, please keep any other comments coming!

p.s. I absolutely love the SS's from the mid 90s in your profile pic. Want to pick one up for track days.

 

[kwick5]

Just curious as to how much time you are spending in that 3500-4000 range on the bike? Also, how does the bike behave from 4500 rpm's and up? Do you still get any of the same symptoms? My 2000 ST2 definitely likes being north of 4000 rpms and is even better when she's sitting above 4500 rpms when cruising around. For example, I'd much rather have her in 5th gear when I'm on the highway at 70-75 mph, only shifting to 6th when I'm going to be sitting at 80 mph or faster.

 

[Beerco]

I'm finding that around 3500 is "where I want to be" when I'm going for a casual ride with the wife. Mind you we just got the bike a few months ago and have put only about 1000 miles on her. I'd say that the trouble spot ends right around 4k and everything north of there seems fine. If a normal bike makes the sound "Baaaaaaaaaa" when running right, the bike makes a "Baapaapaapaapaa" sound. Sounds a little bit like a bike hitting a rev limiter - as if it fires right for a few revs, then lean/rich for a few revs - in the trouble range. Not exactly like hitting a rev limiter but sorta similar. My only other Ducati was a Monster and back then, it had no tach so I have no idea what kind of revs were normal when just tooling around.

I mentioned backfiring earlier - often when riding around that 3.5~4k range the bike will backfire mildly through the airbox when closing the throttle under certain conditions. As I'm writing this, I'm thinking I should check that the airbox is fully seated on the throttle bodies.

One more thing - also yesterday when we got home from our ride, I was jokingly revving the motor while my wife was entering the garage code and once I closed the throttle after revving maybe 5 to 10 times, the bike backfired through the exhaust - pretty loud one but not anything frightening.

It stands to reason that if I'm getting backfire conditions, the bike is on the rich side, not the lean side I'm thinking. It also runs better in the cold than hot. Perhaps I should crack the seal and make some small adjustments to the trim screw to lean it out a touch?

Also perhaps it's more a temp sensor sort of thing as opposed to a TPS thing? I also can't recall ever hearing the fan turn on....ever....but I haven't been specifically listening/looking for it.

 

[Teazer]

Can you just disconnect teh TPS and measure teh resistance as you open the throttle? If so, I'd expect that the readings would be erratic at that spot. I have had a couple of Fords with a similar problem of off-idle snatch because of wear at that point.

 

[Beerco]

Teazer - Yes, that was part of the plan and I totally forgot about it! Thanks for reminding me. I have a decent oscilloscope that can go pretty slow so it should be easy to tell. Back probing voltage and not resistance of course.

 

[kwick5]

In general, I think these ST2's like to run north of 4000 rpms, but definitely check out what others have said. From what I remember when I had a bad temp sensor, the bike felt like someone pulled a parachute off the back while riding. No rpm change, just loss of power for a short period, then it would be fine. No engine noise difference that I remember, but that was many, many years ago. It was also intermittent, not constant so mine wasn't completely gone.

I just replaced both temp sensors while getting my ST2 back on the road a few months ago- quick job with only minor coolant loss if you are quick. I used the replacement part noted in the forums someplace, which are here on amazon. Much cheaper than the $54 each from Ducati and somewhere someone tested the accuracy of them.

https://www.amazon.com/Bosch-Original-Equipment-0280130026-Temperature/dp/B001CO2VU0/ref=sr_1_1?dchild=1&keywords=Bosch+0280130026+water+temp+sensor&qid=1605231773&sr=8-1

I hope you can narrow it down and smooth it out without a 6 hour fairing removal (that's crazy!!!).

 

[belter]

get it on a diagnostic tool and make sure all the inputs are valid, no tps discontinuity, etc.

i would check the closing clearances in case any are large. closing clearance generated running weirdness is usually 3,500rpm ish.

make sure the belts aren't loose. tps set up, throttle balance, idle mixture, etc.

i had an st2 come in once with an issue in this rpm range. had d&d mufflers that were hideously loud. did all the usual tps and tune stuff to no effect. turned out it was rich in that range. i ended up putting a trench in the fuel map to fix it. no idea why.

 

[Stick]

If you want to eliminate the temp sender, just unplug it. It will stay in the "cold,rich" mode. After that, you can plug in a 220 Ohm resistor into the connector. That makes the ECU think it's at 207 deg. F. (But hard to start if the engine is cold!)

This is the sender on the vert. cylinder. The H sender = the dash readout. And yes, it they are OEM, they're garbage. Go with NAPA or Bosch replacements.

 

[ih574]

Ideally, you get someone or something to figure out what the problem is so you're not throwing parts at it randomly. However, I don't always do that cause sometimes I throw a part at something if it can help diagnose without spending service money or finding those who are actually experts at diagnostics. My 2000 ST2 developed a similar stumble and rough running condition under that same RPM range. I replaced the air sensor (552.4.002.1A Pressure sensor) found under the front left upper fairing.

The bike had always run a bit rough under 3K. I just chocked it up to a big twin wanting to run at a higher RPM. But the problem became noticably worse at high altitudes while on a trip from Virginia to Wyoming. In fact on a couple of Wyoming mountain passes, it almost became unrideable. Also, the symptoms extended up into the 4000 - 5000 range but would clear above 5K. Once back in the comfortable 1000 to 2000 ft elevations of the Blue Ridge Mountains, the bike returned to normal I replaced the air pressure sensor anyway, feeling that something was still broken on the bike.

After replacing the sensor, the original rough running below 3000 completely disappeared. The bike was a totally different machine at those speeds. In fact, for several rides I ran at 2000-3000 or so the whole time. I didn't lug it, having heard of potential crank shaft failures when loading the bike at low RPM. But I did short shift and cruise at those RPMs when possible (which was pretty often). The bike was silky smooth. Unbelievable. Added a whole new dimension to the bike's demeanor. Its an absolute joy to ride now, at all RPMs.

Might be worth a look. I paid about US $35 on eBay for a used one and got lucky.

Regards,

Tom C.

 

[Beerco]

Thanks, Tom. The sensors are all pretty old so I've already purchased a TPS (which was kind of expensive) and two coolant temp sensors.

Does anyone know what sort of diagnostic tools are available for these old machines? If there's one that reads out sensor values or even voltages, that would make this so much easier!! Anything available, perhaps PC+interface based that might do the trick?

 

[Stick]

Nothing for the 1.6 ECU. I don't believe a "TPS reset" is do-able on a 1.6. You have to go thru a manual calibration with the TPS.
A DP chip for the ECU made my 1998 ST2 run much better than the stock chip.

My suggestion above was so that you could eliminate the temp sender as the culprit. My ST2 did develop a stumble due to a faulty temp sender. It won't hurt the machine to run it with it unplugged (rich mode). It will give you a go / no-go result that will tell you it's the sender or not. You said you had a scope, so it seemed to me that you're open to troubleshoot.

5 inputs on the older machines (no lambda sensor):
TPS (0 -5V)
air pressure (0 -5V)
engine temp (curves on-line -- Bosch)
air temp (curve on-line -- Bosch)
CPS (on-off pulses)

 

[Beerco]

Nothing for the 1.6 ECU.

Like, nothing available over the OBD port at all?

Since the last post I made, I found some posts about the Guzzi Diag software. Looked under the seat of my bike and found the 3-pin Fiat connector there. Looked on Amazon and found usb/J1962 adapters and J1962 to Fiat 3-pin connectors.

I was heavily involved in Chrysler engine diagnostics on the OEM level way back in the day, 1995~2004, and at least on engine controllers for cars, every sensor value and a number of calculated values were available over the port. Back then, OBDII required us to have certain values available over standard diag protocols but everything was available over the "SCI" interface. We were also required to release everything except super proprietary stuff (like mileage programming) through ETI, the equipment and tool institute so that 3rd party vendors could make scan tools that work with "proprietary" interfaces (in quotes because SCI is a standard serial interface implemented on Motorola MCUs - the guys at Chrysler just basically ran a trace from the SCI pin on the HC11 or HC16 to a pin, possibly with a little protection on it).

Are these sensor values really not available over the diag port? Seems like it would be super easy to diagnose electrical issues with just those 5 sensor values on screen.

 

[ducvet]

The powersports industry has no standardized on board diagnostics, I wish. The available software changes from brand to brand and even in the brands there are different systems depending on generation of ecu used.

Socio
texa
guzzi daig
Tuneecu
centurion
VDST
scanM5x

Are the ones I know of and use most based on the bike I am working on at the time.
Most will let you read the sensor data of many but not all things Ie: the ecu does not flag itself if bad.

 

[belter]

guzzidiag will give you all the info that ecu is capable of delivering. get the cable from lonelec.

 

[Beerco]

So, I guess I must have been awe struck or just hypnotized by that immaculate seal on the ECU but last night, the spell was broken and I went out into the garage and used my thumbnail to break the seal.

The trim pot was at about 10:30 so I backed it out (figuratively) CCW by about 1/8 turn so it was at 9:00 and went for a spin today - HOLY &^%[email protected]%!!!!!! It's a brand new bike!!!! Everything runs sooooo much better now! Although it is kind of lugging from about 3000 to maybe 3700 but, it's making power for a change!

Closing the throttle doesn't have as much engine braking either - which is also a good thing as I raced a 2-stroke for a while and don't care so much for engine breaking. Cracking the throttle isn't nearly as 'surgey' and abrupt as before either.

The exhaust was quite "gasoliney" so I turned it to maybe 9:15 or so and went for another spin - still good but probably better at 9:00. This was alone, we'll see how it is with a passenger!

So, for anyone who may have this issue in the future, the trim pot is a good and easy starting point.

Since I have the coolant temp sensors I'll change those prophylactically over the winter but finally this thing is riding like a Duc!!!!

Thanks for all the advice guys!

 

[Beerco]

Quick update - with the trim pot at 9:15, I did get a bit of stumbling right at about 3800 to 4000 with my lovely and talented passenger. Luckily, I brought my jewelers screwdriver with me and set it back to 9:00, maybe 8:50 (didn't bring my glasses ) and now it's absolutely purrrrrrfect with her on it.