My 2001 XK8 has been setting p0172 and p0175 codes from time to time, so I started doing some diagnostics this morning and find that I have around 40 psi with the key on, engine not running, but when I start it up the pressure goes way up, like 100psi!

My first thought is something blocking the return, but where is the extra pressure coming from? Needless to say, removing the vacuum line does nothing.

My next move is to try another gauge to make sure the high reading is valid.

Any suggestions?

Thanks in advance for any input and Merry Christmas!

 

OK, tried another gauge and still have crazy high pressure when running. I'm thinking I might pull the output hose from the relief valve and run another hose to a gas can to see if pressure drops.

Does anyone know if the is some sort of check valve in the return line? I find nothing in the factory parts breakdowns.

 

Update and a bump. Hoping some Jag nuts are looking on during the holiday. Pulled off the return line and put into a gas can and pressure dropped. So now I'm pretty sure I have blockage in the return line. Have air hooked up now and it seems to be flowing, hoping to let it run thru a while and free up the line. At first it took crazy high pressure to get any bubbling in the tank, now 25-30 PSI seems to be flowing.

 

I've replaced the fuel pressure relief valve on the right hand fuel rail, you can get a Lincoln LS part if u want to try that route as a fix. Mine was leaking, however, not stuck close. It is electrical in nature internally w- a diaphram.

 

. . . and I would not run the engine until you replace the regulator as you are pumping far too much fuel into the cylinder which is going to burn up your $1000 apiece cats . . . quickly.

 

I have the relief valve off right now and it looks nothing like the one shown in the Jag breakdown, it looks just like the one in the tank of my Jeep. It also has a Ford like part number, but it is the earlier type w/o electrics, just a vacuum line. I suspect the diaphram inside has died and a piece of it went into the line. I blew the line out and now I get high pressure, but it flickers around. My next move for the day will be to put teh regulator back in w/o the seal so it will at least bleed off pressure. Even starting it at 100+ psi scares me!

 

Yes, I hope the cats are OK. Hows things in Elijay today? I spent the majority of my life in Cobb County. Bet it's warmer than here!

 

. . . not much. Been rainy and cold but high 60's later in the week. Best place in the world to ride a motorcycle and a sports cat!