I have an ST4s which has done very few miles in the last couple of years. Over the years, I've spent a fair bit of time replacing the in tank fuel hoses and dealing with the usual starter motor problems. Even after long lay offs I've always got it to start no bother. This year I noticed that the fuel tank was leaking from the back, so removed it just to have a look at everything and put it all back. Started the bike and took it for a run - after about 30 miles it started to run intermittently on 1 cylinder. I'm just looking at various options - I've taken the injectors out and measured the resistance on them which is identical. I was going to clean them using the flushing method aired on U tube (usually for cars), but I see that's not an easy option given the way the feed works. Anyway, everything in there looked very clean with no dirt or debris or crap from the fuel present in the filters around the injectors. The in tank hoses are all in good condition and when you turn the ignition on the fuel pump relay works as it should. I'd like to test the sparks by hand cranking it with the tank off but I see you can't do that with the fuel pump relay disconnected. Can you bridge the terminals in the fuel pump plug, so that the ignition system is live and I can have a look at the quality of the sparks.??? I guess it's probably the Brown and white wire plus one other...? Any suggestions?
Does the starter only operate whilst the starter button is pressed or does it run once pressed until the bike starts?
There's no problem with the starter, it runs until the bike starts. The bike starts easily but intermittently goes onto 1 cylinder. I was looking at fuel, but now I'm looking at sparks. I am hand cranking it with the special tool and the plugs out. No sparks. Thought I might go through all the relays associated with the ignition circuit.
Having gone through the fuel system to check for debris etc, I don't want to put the tank back on and connect it all up without checking the ignition circuit. So I'm wondering if the ECU prevents sparks when the fuel pressure is below a certain value. Seems unlikely to me, so I should be getting sparks when I hand crank the engine. I can hear the fuel pump relay clicking as I turn the engine over which suggests it's receiving info from the CPS sensor which shows 950 ohms. I've ordered another CPS sensor because they are cheap and maybe there's an intermittent fault there. I've swapped the relays over (fuel pump and ignition) and the clicking carries on so both relays are ok on that test. Haven't looked at the main 5 pin relay which is no 4 on the diagram you sent, so thanks for that. Just going to have a look at that one.
