S4RS took running like crap. - Ducati Monster Forums: Ducati Monster Motorcycle Forum
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post #1 of 17 (permalink) Old 02-27-2016, 06:56 PM Thread Starter
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S4RS took running like crap.

Went on a group ride 2 weeks back and had some issues. Took it out last night and the issues were still there and got worse.

1. After riding for about 90 miles pulled up at a stop sign, waited a few seconds, went to slip out the clutch and the bike lurched and died. Weird. Started right up, slipped clutch, hiccup in intakes and it died. Started bike, slipped into second and was able to just barely get going. Once under way it ran and shifted fine.

Stopped for lunch and everything was good again.

2. Stopped for gas. After that the bike didn't seem to make much power unless pushing it very hard in a lower gear. Chalked it up to bad gas. Nobody else complained. Ran it out of fuel and filled up with new gas at the end of the ride.

Parked it.

Yesterday fired right up.

3. Nailed the throttle in first entering a highway from a red light. Bike seemed to bang off the redline right away without much power. Thought the clutch might be slipping and some of the previous problems.

4. On highway noticed if I was cruising at 70 in 5th around 5,000 rpm and pulled WOT quickly the engine would bog down like it was going to die. I could hear the engine struggle through the intakes. Bike ran fine if not ran hard. No strange noises or other issues. No CEL.

5. Got to where I was going and pulled up at a light to find the idle around 3,000 rpm. It finally slowed. Then crept back up. If I blipped the throttle it would hang at 3,500 for about 1 minute before very slowly coming down. < That rules out clutch issues.

Today I spoke with some tech friends and they seem to think it's the stepper motor. If so, one recommends replacing the entire throttle bodies. One says he can source the stepper motor for about $800. Another says to just delete the stepper motor altogether by having it's code removed from the ECU. One hold out said he thinks the ECU is fried and giving me problems. Ugh, I hate all this electrics.

Anyone care to add their opinions?

09 Aprilia RS125 plated< NEW info> Now a 144 and back on the road!
06 Paul Smart Sport Classic NFS ever.
08 S4RS Tricolore #081 NFS ever.
The pink Monster has moved away.
97 900SS CR
72 Norton Commando 750
03 KX60 with S4R rear shock,Honda CB350F, Hodaka Ace90, 3x Yam-YGS1, Yam-CS3 200, Vespa small frame, Gilera 106, Puch Sabre, Puch 50 Boy Racer, Benelli 250, Benelli 360, Honda CB350T, and many more.
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post #2 of 17 (permalink) Old 03-09-2016, 05:47 PM
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Haven't been on the forum much due to life issues so I missed the thread.

1) I don't think it's the ecu but rather something telling the ecu to do (x).

2) could be a stepper motor but isn't that for idle purpose only? (Refresh me)

3) I would test the tps first. Rarely, from what I have read, do they go bad but they can send the wrong voltage to the ecu thus the various rpm changes. An ohm meter back probed into the tps could check the voltage at idle and thru the sweep.

It is safer to remove the tps to test. If back probing and the wires touch it's bye to the ecu. When I was trying to get the MV Agusta running I did this several times to the tps. Small paper clip works fine as a probe.

4) Check the ground wire to ecu. Odd that it ran fine then all of sudden the change. (Shot in the dark but question everything)

Probably didn't add much in the way of help or ideas and most of this you already know. Just my thoughts.

1982 Suzuki GSX400E

Last edited by toytuff; 03-09-2016 at 05:50 PM. Reason: Text
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post #3 of 17 (permalink) Old 03-10-2016, 09:05 AM
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The stepper will only have an effect at idle.
Does the check engine light come on ?? - if not then you can rule out any sensors.
The TPS will cause a miss in the engine at a certain throttle position and also the check engine will come on.
Will need more info before making a diagnostic.
I have a good idea what is up with it but more info please.
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post #4 of 17 (permalink) Old 03-10-2016, 08:06 PM Thread Starter
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Quote:
Originally Posted by Mister Ducati View Post
The stepper will only have an effect at idle. That's what I was wondering when my service manager friend told me what he thought it was, then one mechanic came out and backed him up saying they had a similar issue recently.
Does the check engine light come on ?? - if not then you can rule out any sensors. I had not seen any codes other than "Maint" as I'm due for valves and belts.
The TPS will cause a miss in the engine at a certain throttle position and also the check engine will come on. One of my first thoughts was TPS sensor.
Will need more info before making a diagnostic.
I have a good idea what is up with it but more info please.
Starts right up and sounds great. One thought I had was a valve not closing completely leaving me with a compression loss. It fires up too easily. I've been meaning to do a compression test but just haven't had the time or energy to pull the plugs. Both butterflies open completely. Brand new battery holding a great charge. Hoping it's not a loose flywheel nut and shavings on the induction pick up for the spark. I wouldn't rule out a bad coil giving an erratic spark.

Ordered cables and software to see if it can tell me anything.


I'm all ears.

09 Aprilia RS125 plated< NEW info> Now a 144 and back on the road!
06 Paul Smart Sport Classic NFS ever.
08 S4RS Tricolore #081 NFS ever.
The pink Monster has moved away.
97 900SS CR
72 Norton Commando 750
03 KX60 with S4R rear shock,Honda CB350F, Hodaka Ace90, 3x Yam-YGS1, Yam-CS3 200, Vespa small frame, Gilera 106, Puch Sabre, Puch 50 Boy Racer, Benelli 250, Benelli 360, Honda CB350T, and many more.
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post #5 of 17 (permalink) Old 03-11-2016, 03:56 PM
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I'd consider checking the coils. I had to replace them in my S4Rs when it ran erratically, similar to your descriptions. Seemed to start and idle OK, but given any kind of sudden throttle it would struggle. My first thought was TPS too, but took it to a shop and new coils and a new battery solved my issues. On the other hand, if you need a new TPS, I'll make you a good deal on the one I bought new and never used and has been sitting in my garage. Hope you get it worked out soon!

-MI
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post #6 of 17 (permalink) Old 03-12-2016, 09:10 AM Thread Starter
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Originally Posted by mirwin717 View Post
I'd consider checking the coils.

So you are saying that the bike would idle well and pull away ok but then get screwy in the higher revs? I've had coil failure before, on vintage British bikes, and it was either the coil worked or it didn't. The bike would only run on one cylinder. I've worked on old Vespa scooters that would run great for a few minutes and then start to shut down as the coil got hot but they were paper and wire wound coils, as the copper wire heated it would expand through cuts in the paper and begin shorting out.

I can't think of a good way to test a coil for bad high speed issue other than ordering a Gunson see through spark plug to see if the spark gets erratic while revving in neutral and I'm not sure if it would give me bad results while not under load. I haven't looked at the S4RS system yet, but I know on my 900SS there are exciter boxes that I have heard go bad. Two more things to look for then.

edit: Well should've checked them out first. I see the coils are mounted directly to the spark plugs on these bikes.

09 Aprilia RS125 plated< NEW info> Now a 144 and back on the road!
06 Paul Smart Sport Classic NFS ever.
08 S4RS Tricolore #081 NFS ever.
The pink Monster has moved away.
97 900SS CR
72 Norton Commando 750
03 KX60 with S4R rear shock,Honda CB350F, Hodaka Ace90, 3x Yam-YGS1, Yam-CS3 200, Vespa small frame, Gilera 106, Puch Sabre, Puch 50 Boy Racer, Benelli 250, Benelli 360, Honda CB350T, and many more.

Last edited by caferacermike; 03-12-2016 at 09:12 AM.
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post #7 of 17 (permalink) Old 03-12-2016, 01:44 PM
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As far as I can tell from your symptoms. I would say it is most likely due to water in the fuel tank/fuel filter.
You need to take a few steps back and think about it.
Did it start to have the problem just after you worked on the bike ??
Or has the bike been parked outside in the rain lately ?? etc. etc.

Coils or plugs would create a backfire in the exhaust.
Stepper would effect the idle only
TPS would show up as a engine miss/cut out at a fixed throttle position or would not start up..
You mentioned that it bogs under acceleration and that the idle is sporadic and the symptoms are intermittent.
These are symptoms of a lean fuel mixture which could be a possible faulty fuel pump that does not produce enough pressure or water in the fuel.
My reasoning is that you mentioned that there is no check engine light coming on so that will rule out most of the electronics.
But the only thing that will not cause a check engine code is the fuel pump not having enough pressure or water in the fuel.
If you disconnect the fuel pump electric circuit this would produce a code as the ecu sees that the pump is not connected. But the ecu can not see if there is pressure.
But in your case I say that it is down to water in the fuel.
These bikes are notorious for getting a blockage at the fuel cap drain pipe/fuel tank vent pipe.
This would result in water accumulating around the fuel cap flange and when you open the cap to fill the tank the water would enter the tank without you seeing it. And then over a few tank fills you end up with the symptoms as shown.

From my experience it is often something simple that most people tend to overlook and go in too deep for nothing.
I would go ahead and empty the tank in a clear or white plastic container and look for signs of water in the fuel.
It is easy to distinguish the water as it does not mix with fuel and is heavier than fuel so therefor it will sink to the bottom and look like a blob or bubble of something in the fuel.
I could be wrong but I am betting otherwise.
Let us know what you find.
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post #8 of 17 (permalink) Old 03-12-2016, 08:13 PM
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You can go to a camping store, buy a two dollar siphon, siphon the gas out into a glass container or can and check for water in the gas. I found mine at a Tractor Supply store. Also Farm Fleet, Fleet Farm stores. It's used for filling lanterns, stoves and such. Works very well. Camping section, not auto.

Might save removing the tank for now but a new fuel filter might be in order at some point.

1982 Suzuki GSX400E
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post #9 of 17 (permalink) Old 03-13-2016, 11:00 AM Thread Starter
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I'm doubting I have water in my tank. I guess I could have gotten it from filling up, but I ran that tank so low I honestly thought I might get stranded.

I don't wash my bikes. I have too many for any one of them to get dirty. I use a detailers spray and microfiber rags, no car wash for me. I have only been caught out in the rain once on this bike and it was 3 years ago.



The tank opens easily with no vacuum after a ride but I will check the vent line.


What gets me is that the replies all leave out the single fact that the last time I rode the bike, at every stop it would be screaming at 3,000 rpm for the idle unless I kept blipping the throttle until it would finally slow down.

A bad coil won't make the idle run higher. I'm pretty sure a dead fuel pump won't either. That's why deep down I worry it's the ECU. If it's gone screwy I could see it creating an erratic spark or fuel issue, and then tell the steeper motor bad information leading to a super high idle. Other than that I'm running out of ideas. So if any of you think a bad fuel pump will cause a high idle I'm all ears.

Hopefully this cable set shows up soon.

09 Aprilia RS125 plated< NEW info> Now a 144 and back on the road!
06 Paul Smart Sport Classic NFS ever.
08 S4RS Tricolore #081 NFS ever.
The pink Monster has moved away.
97 900SS CR
72 Norton Commando 750
03 KX60 with S4R rear shock,Honda CB350F, Hodaka Ace90, 3x Yam-YGS1, Yam-CS3 200, Vespa small frame, Gilera 106, Puch Sabre, Puch 50 Boy Racer, Benelli 250, Benelli 360, Honda CB350T, and many more.
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post #10 of 17 (permalink) Old 03-13-2016, 12:16 PM
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Have you checked for air leaks?
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