Hi Jaglovers
I hava a problem with my 4.0 XJ40.
When the engine is cold and I start it, there’s no problem.
While the engine is warm, also after one or two hours,
it mostly won’t start.
I have to hold the key and then until maybe 10 seconds
the car will start.
Does anyone know the problem? By the way, the fuelpump
is working well.
Best regards, Gregor
When I had that problem it turned out to be a faulty Fuel Pressure Regulator (FPR) but it can also be caused by a faulty check-valve (NRV) in the outlet from the fuel pump.
In either case it results in the pressure in the fuel rail dropping* instantly the last time the engine was shut down because the fuel returns to the fuel tank - in the case of the FPR through the return line and in the case of the NRV the feed line That sudden loss of pressure in the fuel rail of a hot engine results in the fuel vaporizing and effectively causes a ‘vapour lock’ in the fuel rail.
[*On engine shut-down, pressure in the fuel rail should be maintained at about 21 psi - called “the hold pressure” - for some considerable time. In fact it often increases for a period after engine shut down due to latent heat in the fuel rail - see this:
http://www.jag-lovers.org/snaps/snap_view.php3?id=1357201999]
When you next try to start the engine of course there is no liquid fuel in the fuel rail so it takes a few seconds of cranking for the pump to get up sufficient pressure to start the engine - around 40 psi.
You can determine whether the fault is the FPR or the NRV at the pump by using a fuel pressure gauge, clamping the flexible fuel feed/return lines in turn immediately on engine shut down to isolate the faulty item to stop fuel leaking back to the tank through that line.
Another thing you can try, instead of cranking it for ten seconds, is to take advantage of the ‘priming burst’ from the fuel pump each and every time you switch on the ignition by doing the ‘key cycling trick’. Turn the ignition ON,OFF,ON.OFF,ON … half a dozen or more times and only then engage the starter. If the engine fires up immediately, your problem is definitely lack of ‘hold’ fuel pressure.
Hi Bryan
I tried it with the key cykling trick and the engine starts immediately.
Thank you for your advice and best regards,
Gregor