Hello,
I would generally follow a series of tests to diagnose this. Realizing that it's an intermittent issue on a boat, I would still attempt to find a way to confirm the plugs are sparking and that the fuel rail is at the required pressure.
I attached a fuel pressure gauge to the engine. Pressure is good. The only thing I see not normal, is that the pressure in the line drops from 50 to 10 in 9 minutes when the engine is turned off. But that doesn't seem to affect subsequent starts. Look at the video below. For spark, I bought a spark tester and increased the gap and the spark seemed good to me
If you'd like to look at potential causes, there are a few hunches that may or may not be right. First, if one or more of your injectors is leaking slightly after the engine is shut off this can saturate the intake with fuel. Cranking the engine will cause a hard start as the injectors deliver more fuel. Opening the throttle can allow more air into the intake to draw away some of the excess fuel. Opening the throttle to 100% typically triggers "clear flood" programming which causes the computer to decrease the amount of fuel delivered. I am unable to see the injector on-time in your hard start video but I would suggest watching this value to see if it decreases substantially shortly before the engine starts.
I will check the injector time ON during cranking. When I had the injectors removed, I connected them one by one to a fixture I made with a steel pipe, filled the pipe with fuel, and applied 45 psi or air, and waited 1 minute each and none of them were leaking.
Another potential cause could be lack of fuel at the rail. A fuel pressure gauge is invaluable during hard-start diagnosis and can quickly tell you if your pump is working as expected.
see above
Forcing the engine not to start by disabling the coil would allow you to watch the scantool displayed rpm during cranking. This could help you determine if the low value seen during the hard start is a normal value. We've had crank sensors cause intermittent issues in the past. It's rare but it can happen.
ok I will do that (disable the coil). One thing I will try to do, is to borrow a tachmeter from my work and see if the engine is cranking 125 RPM like reported by the gateway. If yes, it is too slow to start, NO? I think a ECU goes from cranking mode to running mode around 400 RPM, is it right? Maybe my problem is there; bad CKP or engine not cranking fast enough. But from the sound of it, it seems to turn fast enough...
Finally, fuel is a mixture of chemicals and the mixture changes through a season. Additionally, the ingredients added can change through the years. In some cases programming that worked 20 years ago is not optimum today. This can be tougher to figure out. For some folks the answer to this problem is to find a routine that allows the engine to start as quickly as possible and just follow it when there's a problem.
Yes, harder to figure. But other people with the same engine on boat forums don't have that problem, so I suppose the programming is not too bad???
Here is a video of a cold hard start, followed by 2 cold easy starts. The fuel pressure gauge shows that there is enough pressure, even if it drops when the engine is stopped.
https://youtu.be/pIFu_HpI8is
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