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I ride a 2002 ST4s that was bought new in 2008 and has now travelled 8800km. I have fitted a power commander and carbon mufflers and done some minor alterations to the air box. Spent some time setting up suspension and am generally happy with the results.

There has been an intermittent problem almost from new and that is the bike sometimes starts on one cylinder and if left idling will usually pick up the second cylinder. Recently on a trip it dropped a cylinder and I managed to make it home on one cyl. Since then have started checking to try and locate cause. I noticed that when cranking the vertical injector will give one charge then nothing. Have had the ECU, an IAW 59m checked by Avanti and they said it tested ok but suggested that the immobilizer may have failed. We agreed to reflash the ECU and remove the immo function. Refitted to bike and took out the immo, tried to start started briefly on one cylinder and not a kick since. Had an additional battery connected to make sure there was sufficient voltage.

I am starting to run out of ideas, can anyone offer any suggestions?

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I am no expert on bikes, but wondering if you ensured the grounds (earth connections) are good to the injectors and to the computer? –  Paulster2 Dec 27 '13 at 22:53

2 Answers 2

up vote 1 down vote accepted

I doubt it would be the ECU. Those are typically all-or-nothing. Sounds more like a bad wire or electrical connection.

Test the wiring harness to the injector with an analog volt meter. Put one meter lead to ground and the other on an injector lead while the motor is idling: If the needle doesn't swing then try the other injector lead (if there are two, one would be power and the other ground). Move the injector wire around because your looking for a break in it. If the needle suddenly stops swinging -- or starts swinging if it wasn't at first -- they you have a broken wire in your harness and it will need replacing.

If you are getting voltage to the injector (no broken wire harness) then you're injector needs replacing. I don't know what the resistance values are but if your ohm meter reads infinity then it's bad. The reason why it would work and then quit is that the wire coil in it that operates the solinoid is touching at the break point but when it warms up the object expands and the break in the wire becomes bigger and creates a gap that electricity cannot travel across and thus it stops working.

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