Faulty TPS ? - MVAgusta.net
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post #1 of 20 (permalink) Old 01-13-2013, 03:28 AM Thread Starter
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Faulty TPS ?

For a few years now I've been chasing an annoying intermittent problem..... Symptoms have, until lately,been so intermittent that it might happen once in 6 months, often after a service so I'd blamed it on a dodgy connection somewhere on something that gets unplugged when the tank comes off and/or the spark plugs removed. More lately I can be pretty sure it will happen at least once an hour.

Any how I'll try to explain what happens.

Whilst riding along at a constant speed, on a small throttle, 120km/h so say 6000rpm the bike would stutter/shudder as it lost power briefly (engine power, all electical stuff still working as far as I can tell). Accelerate by opening the throttle a decent amount and it would clear immediately, accelerate perfectly. It may or may not stutter again once regaining the constant speed. Open the thottle a little bit and sometimes it didn't clear at all. Knock it down a gear or three, maintain constant road speed so now at say 8000rpm and it was worse. Open throttle and roar off down the road no problem at all.


The stuttering it appears is the fuel being cut. There is no back fire/bang from the exhaust at all.

Recently the stutter has got worse and more frequent.

I can confirm after testing the last week that opening the throttle fully clears the problem every time, at least for a while.

My guess is there is some crap in the tps that is getting in the way sometimes, breaking the signal to the ecu, so the injectors are cut completely as the ecu doesn't know what the throttle position is. This is certainly what it feels like...

Anyone else think it is the tps or want to offer another explaination ?

Anyone ever taken a tps apart ?
Is it just a variable resister/potentiometer ?
Is it servicable/cleanable or do I just get another one ?
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post #2 of 20 (permalink) Old 01-13-2013, 07:21 AM
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Sounds like an intermittent fuel starvation,

have the fuek injectors been removed and cleaned ?

Try changing for a new set of spark plugs and see if this helps ( I imagine this would have routine during the services) ?

Are fuel lines and fuel pump in good working order and condition ?

The above is where I would I would start before going to more complex and expensive procedures.

Good luck sorting out,

George
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post #3 of 20 (permalink) Old 01-13-2013, 03:56 PM
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Very hard to distinguish a fuel miss and something electrical. For my vote, I would be looking at the fuel system - hoses, pump connection, filter and injector clean, tank venting, breather hoses etc. Also check the tightness of the throttle body seal to the manifolds.
I am presuming the vacuum lines haven't gone hard?
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post #4 of 20 (permalink) Old 01-13-2013, 07:12 PM
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Plus 1 for fuel system.

My brutale was doing a very very similar thing.

Took a while to find it, but a full refresh of the fuel system fixed mine.

New filter, clean the screen, new hoses, new orings on the connections, injectors removed and professionally cleaned and serviced, and cleaned the rail with carby cleaner, a rag and compressed air.



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post #5 of 20 (permalink) Old 01-13-2013, 07:37 PM
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The fact that it's getting worse as your bike ages, indicates to me as well it is a fuel problem. When was the last time you had the pump assembly out of the tank?
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post #6 of 20 (permalink) Old 01-13-2013, 07:42 PM
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I'll jump on the fuel system wagon as well Richard. Replacing the TPS sensor is easy, but setting it up right might be a bit tricky.

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post #7 of 20 (permalink) Old 01-13-2013, 08:00 PM Thread Starter
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The hoses inside the tank were all replaced a while ago, pretty sure the problem was happening before then.

I can't remember for sure if the fuel filter has been replaced since the problem first occurred. It used to get replaced every 12k but I'm 95% sure hasn't been done for a while now.

I guess I'm about to find out how to remove the pump etc from inside the tank and replace that filter...
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post #8 of 20 (permalink) Old 01-13-2013, 09:04 PM
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As Carl said, it appears age related, so I would be looking first at anything that is rubber - orings, hoses, vacuum lines, vacuum line caps. That stuff is relatively simple and cheap.
I reckon you will be looking for an air leak rather than a fuel supply issue.
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post #9 of 20 (permalink) Old 01-13-2013, 09:14 PM Thread Starter
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Would an air leak cause ALL four cylinders to shutdown ?

I know one of the breather hoses from the airbox to the crank case is cracked, so a good chance there are others that need to be replaced too.
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post #10 of 20 (permalink) Old 01-13-2013, 10:28 PM
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I seem to think, that if it was an air leak John, it would be permanent, as in a hose on one of the balansing tubes wont go away after it formed. In my case it just caused the bike to miss on the cylinder involved.
When I had a blocked breather on my fuel cap though, it affected all cylinders, a bit like hitting the rev limiter Richard, does it feel like that ?
Tricky one this.

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