Hello all. I'm new to this forum. I need help with solving a P0172 and P0175 too rich condition on the XK8. I don't drive it much. It has sat for a couple years with me starting it at least once a month. It has passed the CA emissions test for the past couple of years since I purchased it back in 2016. But back in 2021 it developed these rich codes so I never was able to get it to pass the emissions test. The intake tube, manifold and vent tube from the intake tube to valve cover doesn't have any leaks. I replaced the fuel pressure regulator since fuel was leaking past the vacuum nipple into the hose going into the throttle body. It still triggered the rich codes. I noticed when I first bought it i could hear a somewhat loud hiss in the fuel tank cycling on and of from what I assumed was the fuel pump. But since I started getting these rich codes, I no longer hear this audible hiss. I did a fuel pressure test today. It's ready well over 100 psi. When I disconnected the return line after the FPR and attached a hose to a water bottle, the fuel pressure read normal around 44-45 psi. And when I attached the return line back to the FPR outlet and started the car, it shot back up to over 100 psi. The needle on the fuel pressure gauge maxes out at 100 psi, and it was pegged past that. I tested the fuel pressure gauge on 2 of my other cars which was a 1999 BMW 540i V8 M62TU and 2002 BMW X5 V8 M62TU, they both read around 45 psi.

What could cause this, "clog/restriction?" I'm thinking this is why I'm getting the rich codes. Please help. Thank you.

 

Could be the VVT solenoid O-ring seals. They bake in the engine bay, get hard and brittle after just a few years, then begin to seep oil and air. We have owned my wife's 2006 XK8 since early February 2012 and it is currently on its third or fourth pair of these seals....

 

Hmm. So you caught (good catch!) the leaking FPR and replaced it? How long ago and did the problem come with the change out?

I don't know if there is a valve in the return line but I would think on a quiet day, if you blew into the line or pressurized it you would hear bubbling in the tank or the sound fluids moving... I also don't know an easy way to open the line under the hood to access a way to force air into it.

What brand FPR and are you sure you got that connected properly? I have had the experience more than once of something new out of box being, defective. If it's not tooooo late I would suggest returning the regulator FPR and seeing if fitting a second one makes a difference...

I wouldn't drive it anymore with that kind of fuel pressure.... Lots of excess fuel reaks havoc on CATs,,, and I ain't talking Jaguar's

 

You seem to have diagnosed the root cause right there. That return line should just drain in the tank. Try and follow it. See where it connects and check the flow section by section. Or try and run something through it (electrical wire?) to see how far down the blockage is. There are other options, like trying to drain as much of the fuel from the return line as possible and replace it with gas plus injector cleaner in the right concentration. See if there are metal sections that have been crushed somehow. Try a vacuum pump instead of pressure.

Best of luck, keep us posted.

 

I would remove the fuel filler cap and 'gently' try to blow air into the fuel return line from the engine compartment to the tank like JayJagJay suggests.
Did someone replace the fuel pump and try to drag the fuel tank 'partway' into the boot area? (those fuel lines get BENT and damaged when people try that 'trick')

NEVER pull the tank rearward with the fuel lines connected!!!!!!!!!!!!!!!!!!

FPR replacement part could be faulty?