JK CRD won't start but runs fine :)

[bocky]

Hi Everyone, thanks for the help.

I have replaced the battery (was 3 years old) and still won't start.

I can get pressure around 25000 psi when driving maybe a little higher, will check tomorrow. The maximum whilst cranking is around 1900 psi.

The suggestion of a faulty rail pressure sensor got me thinking so I disconnected the sensor and the car starts perfectly in about 1 second. Every time! My OBD2 logger then reads 24000psi with the sensor detatched (guessing that is open circuit for the sensor)

With the sensor disconnected the car drives pretty well today, maybe losing power at high revs....

So does this mean the sensor is faulty?

[Banshee]

I would say it is a good bet. Good find!

[RLT]

How many KM's have you got on the JK ?

[Hayesio]

My thought's are that your rail pressure defaults to the maximum, 24,000PSI, when disconnected (they probably program it like this so the vehicle is not disabled all together in the event of rail sensor failure). I'm surprised it doesn't go into limp mode after starting. Rail pressure needs to be 2,000PSI before the engine will start - so you've worked out how to solve that problem. You could have a faulty sensor, but the fact that it works at all, when connected, suggests that this is unlikely - sensors generally fail completely or intermittently, but rarely fail in a manner to give lower readings. But that's not to say its not possible. Maybe try starting the engine with it disconnected, then connect it when running and see what the OBD2 PID reads.
To me, unfortunately, it sounds like your pump can't produce the pressure required for starting, 2,000PSI. In that case, you will need a new pump. Very expensive.