[R.T.]

While you wait.

Say you have a slightly leaky injector. Overnight the system drains down into the tank. When you crank you get ‘fuel’ pressure, but it’s pressurised air in the rail and because there is no excess fuel return system it has to bleed out through the injectors, which takes a long time because all the pipework and filters are full of air.

You could try cracking the nearest joint to the injectors which is accessible and repeatedly priming the system until you get fuel only coming out. Then tighten the joint (while the pump is running if necessary to prevent the fuel running back), and try starting.

 

[R.T.]

[QUOTE="156and33,
Does this hypthesis fit with the fact that I can crank the engine for as long as I like on the first go and it does not start - wouldn’t any air have plenty of time to be purged from the system?
[/QUOTE]

Only if there was an anti-flooding function in the ecu that turned the injectors off after a certain time cranking; but that is speculation. I’m afraid I know little about the JTS, mine is a diesel. Fuel draining back seemed like the most likely cause of your symptoms and when I saw in elearn that there is no fuel return system I thought that could explain why it took so long to start the engine, despite fuel pressure showing in your graphs (the slow pressure rise in graph two might be the air being compressed?)

The outlet port of the HP pump might be a good place to open the system? It would still leave some air to purge but hopefully the difference would be noticeable. Elearn indicates that the lift pump pressurises the whole system up to the injectors so you should get air/fuel coming through the pump.

I suggested an injector leak because if it was further back I assume the engine would fire a few times as the fuel in the rail was used (there is a thread where this symptom happened but that was not resolved either). I’m not sure if a stethoscope would find a leak, if you can eliminate background noise: perhaps?

If you get fuel wet plugs after the first attempt then the problem isn’t fuel or at least not lack of fuel, but spark/compression, so that would be a good test to do.

Time to sleep here.

 

[R.T.]

not sure why the fuel pressure does not rise to 50 bar during cranking

The last petrol car I worked on delivered a measured 2.5 times stoichiometric air/fuel ratio* during crank, which may be more than the HP pump can deliver since when running only about 1.1 times would ever be required. Apparently the engine is designed to start from lift pump pressure, which presumably is why it is comparatively high.

Started second go but that was not very convincing as if the engine was flooded (3-4s).

only 375kg/hr looks rather restrictive when you should see 460kg/hr at 6400rpm for the JTS.

You have fuel going in (wet pistons) so spark or compression. I can’t explain why it would only affect the first start attempt but maybe try a throttle body self-learning procedure in case it is starving the engine of air?

* That was port injected, direct engines might need a bit less?

 

[R.T.]

Why does MES only show “MAF (throttle closed)” and not actual live airflow data like my other interfaces?

In mes you can select ‘Air quantity’ and/or ‘Mass air flow (throttle closed’ ie: flow when throttle is closed, only.

I’m not sure if it is relevant but have you seen the ELM 327 interface warning here: Multiecuscan - Diagnostics software for Italian cars

but the JTS can suffer from poor injector spray pattern and then inlet tract carbon could play a part.

There doesn’t seem to be much else left but it’s still strange that it will only start on the second attempt in the morning. Would it be worth monitoring the inlet mode (short/long) the injection time, spark advance and throttle position during each attempt to see if they change? If choking/fouled injectors prevent starting on the first attempt the ecu might be changing strategy for the second? (I’m assuming that for the rest of the day the air and engine are warm enough to start first time, hence it started first time at 3pm after the maf change. When did you start it after doing the plugs?)