Hi All!

I have a 1998 XJR which runs great -- except on rare occasions it cranks for a very long time before starting. The problem seems random and does not seem to matter whether the car is hot/cold or wet/dry.

My first guess was a fuel issue, so I borrowed a fuel gauge and checked on the rail multiple times (both hot and cold). Of course I could not reproduce the long starting problem, but I did notice what seems to be to be strange behavior. I consistently saw this:

Attach gauge, it shows zero fuel pressure.
Turn ignition to on.
Gauge jumps to 42, then immediately back to zero.
Begin cranking, gauge jumps to 42 and car starts normally.
Gauge remains around 40-42, and car runs fine.
Turn ignition off.
Gauge immediately returns to zero.

I would expect the pressure to remain around 40 all the time, so I suspect a fuel pump check valve -- however I have had a couple folks inform me that maybe this car is designed to relieve fuel pressure from the rail when not running -- and I could not find an answer to this specific question in previous posts.

So I'm asking the experts here! Is the above behavior normal for an XJR or do I indeed have a bad fuel pump check valve -- and if so, do I replace both pumps? or just one? I see numerous how-to's on how to replace the fuel pumps but want to make sure that is the true problem...!

Thanks for any insight!

 

Sounds like you have a bad check valve, regulator, or injector if your fuel pressure is dropping instantly at shutoff. The pressure should bleed down slowly not dump instantly. I don't think the hose after the fuel pressure regulator is crimp friendly; you may have to make a adapter to see if your problem is the pumps or the pressure regulator.

 

Long cranking when starting is usually an indicator of a bad secondary fuel pump. The car stars on the 2nd fuel pump and then switches to the 1st. You can jump the fuel pump relays to individually listen for the pumps running. This is well covered in this forum.