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Discussion Starter · #1 ·
Greetings one and all. Having owned a tornado and a TNT899 before, I decided that selling the TNT was a bad move. I found another which was a bit of a fixer upper and set about it.
Ive sorted the mechanics and cosmetics but its got a problem that is beating me.
Starting is and art. If you dont hit the starter immediately the ignition is turned on it will not start. It always does start if you are quick and warms up just as intended. Once it gets warm and idling, it will just stop just as if the ignition has been turned off. Switch the ignition off, back on and away it goes right until it stops again.
If its being ridden it runs as sweet as you like however junctions and red lights will always be met with a stall if you dont keep blipping the throttle.
I have carried out some rudimentary tests and have found that the switched feed to the injection relay is switching off. All power to the coils, injectors and fuel pump disappears. When you turn the ignition on there is a click from the relays and about 2 seconds later another click and this is the switched feed switching off. Get it running and riding all is good. Let it idle and within a short period of time it stops.
Its booked in at Bennetts however due to unfortunate circumstances they can look at it until January.
The bike suits me really well as having lost my lower right leg seat height is important however having to put my feet down quickly if it stalls is not great.
As a note, the stepper is new and working it idles at 120 to 1300 rpm, the mechanics are bang on.
If anyone has any idea what the fault is I would be grateful for a pointer in the right direction.
Thanks All
 

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That's an interesting problem. Never seen it before.
Thinking out loud ...
  1. I wonder if the ECU knows if there is oil pressure or not? It appears that the problem only occurs when the revs are at idle, or below, and if the oil pressure switch is dodgy ....
  2. by law, the fuel pump must not run beyond a few seconds if the engine is not running. Turn on the ignition and the pump runs, then shuts off. I wonder if the ECU is also controlling the injection relay, coils etc. ?
.. haven't thought these possibilities through though. I don't have a TNT899 or its wiring diagram to check.
 

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No good with spanners....
MV F3 RC, TNT 899
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I have a tnt 899 wiring diagram if it helps…….. what you describe is a new one on me🤔🤷‍♂️

fred
 

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Can you try just raising the tick over a bit like to 1300 /1400 or even 1500, just to see if it still cuts out. All you are doing blipping the throttle is raising the revs , giving the fuel more air. Is it running really rich on tick over.
 

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ECU doesn't know about the oil pressure, it only goes to the dash, so strike that thought.
The injection relay, controlled by the ECU, supplies power to injectors and coils. The fuel pump is separate. So if the pump, coils and injectors are being switched off, the ECU thinks that is the right thing to do. It can't be the tip over switch, because that wouldn't be rev dependent .... unless there are heaps of vibes at idle ??
Idle fueling is definitely worth looking at.
 

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Discussion Starter · #6 ·
Thanks for the input guys. It’s quite a frustrating problem not least of all because the bike runs and rides well. Not owning decent diagnostic equipment doesn’t help. It’s interesting to note that if you hold the engine speed to around 2000 rpm it doesn’t stall but below that it’s almost guaranteed to stall. The fact that you have to flip the kill switch off and on before it restarts doesn’t help. It will keep me entertained if nothing else and hopefully Bennett’s will sort it if I can’t 👍👍
 

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Get tuneecu it is inexpensive and worth having. It can give clues about the engine running. do you know anyone with an exhaust analyser to check Co at idle and just above? You could have a bad connection somewhere. Rick had issues with the side stand switch giving intermittent cutting out. Good luck
 

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The fact that you have to flip the kill switch off and on before it restarts doesn’t help.
I had that trouble with my TreK1130, plus frequent fast idle. I put it down to the stepper getting lost. Switching off and on again resets the stepper. The problem was minimised by setting the idle to 1300-1400rpm. I found a dodgy TPS contributed to low speed trouble. It had poor contact at 7-8% where it frequently sat in cruise, as I proved by recording the TPS% while rolling the throttle through the range with engine off. The fault caused erratic, high TPS% reading at that throttle position, so the injectors delivered more fuel than required, causing the O2 sensor to read rich. The ECU adapted to try and correct the O2 feedback, reducing the fuel across the range after cruising for a while. That made the bottom end too lean, so the engine would conk-out on return to idle. A new TPS and adaption reset gave an instant improvement. Work on the map based on TuneECU datalogs improved things further, avoiding the adaption frequently chasing it's tail. I subsequently found the idle air control valve spigot was not sealing in the air box, allowing dust in. Scoring on the stepper motor plunger indicated some big particles had been in there and jammed it. I fitted a used Triumph stepper with new housing and fitted thicker section o-rings, plus air filter grease to seal the spigot. The stepper seems to be working much better now. No more intermittent fast idle. Occasional slow hot idle but very rare stalling. I wish the stepper would just control cold idle and butt out when the engine is warm. Unfortunately it seems the IACV is supposed to help control the emissions at low throttle openings, so it is always moving with throttle changes and can lose it's place. However the bike is very civilised now and a pleasure to ride at low speed, as I often do in the bush.
 

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Discussion Starter · #14 ·
Thank you for that input. I am of the opinion that the tps or stepper are the culprits and your input would suggest this is the case. The bike has a new stepper fitted however I don’t have the time at the moment to delve further. It’s booked in at Bennett’s early in the new year and I’m sure they will sort it out. It’s a bit of a pain as it rides really well and suits me. I will keep everyone posted in due course 👍👍
 
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