Hello ,

Since ive got problems with my jag. Does not start so good crancks but takes long to start up and in midrange holds back a bit and sounds different. Ive checked the fuel pressure as written in the handbook disconnect vacuum from fuel pressure valve and got around 45 psi and then reconnect and it has to be around 38 and it is . Now the big question can i drive a bit with the fuel pressure valve disconnected and have some more psi to see if the car will run good in midrange and starting ? My suspects are the fuelpumps.

Thanks ,

 

Since you have a fuel pressure gauge, what you can do instead is to tape the fuel pressure gauge to the OUTSIDE of the windshield and go for a drive.

 

And what should i read or not read on the gauge ? Does the pressure needs to stay 38 psi like idile ?
I hope to find something wrong on the car so i can fix it

 

Ok got some numbers while driving any speed under 100kmh it stays around 38 psi and when full throttle sprint it gets aroud 58 59 psi and half throttle around 50 are these numbers normal ? And when i shut off the engine the fuel pressure rises slow to 44 /45 psi

 

That all sounds fine to me. The gauge pressure of the fuel rail should be about 40 psi above manifold pressure, so your readings are about right- lower when the manifold is in vacuum and higher when the SC makes pressure.

The key to figuring out you problems is almost certainly to monitor the STFT and LTFT while havnig the sluggish response.

 

The specification is 3 bar.

From sciencemadesimple.com:

3 bar is equal to 43.51 psi

The pressure is measured relative to absolute manifold pressure.

The rise at shutoff should be quite rapid if you are only observing the change due to the change in pressure at the manifold.

If it is slow, I might suspect a kink in the hose between the manifold and FPR, or a lazy FPR internal mechanism.