I let my 99 xk8 sit due to working from home since Covid and I�m now trying to get it run again for my 16 year old son. I have fixed bad fuel injectors and coil pacts but started getting a lean in both banks once those were handled. I have replaced the leaking fuel pressure regulator and the fuel filter. At this point I�m thinking I have a defective regulator or the cheep O�Riley fuel pump I did years ago is just not pumping enough fuel. One thing I have noticed is when I replaced the fuel pump years ago I would hear it buzz when I turned the key to the on position. I don�t hear anything now but I do hear it when I force the relay closed. So the question is does this sound like a fuel pump issue? If so would you think I should replace the aftermarket pump with a oem one or could this be a different issue? Any suggestions would be appreciated.

 

Has it got 5-year-old fuel in it still?

 

Have you swapped the fuel pump relay for a different one? I think that the fuel pump should run when you turn the ignition on after the car has been standing and the pressure in the line has dropped.

Richard

 

no I have been through a number of tanks. Was able to get a temporary registration while I work through the gremlins.

 

I have but this makes me wonder if the one i swapped it for is the correct type. Where it runs still I would think it is but I will double check.

 

so have you also checked for air leaks - vvt seals leaking, cracks in the air intake bellows, leaking part load breather tube, maybe try cleaning the MAF or smoke test the car

 

To rule out fuel pressure issues you need a pressure gauge. You can get a kit on Amazon for around $30. Attach the gauge to the Schrader valve on the fuel rail. I forget the exact pressure but it should be in the 50psi range at all times.

 

I apologize for the slow response my father passed expectedly but unexpectedly if that makes sense. Any ways I just did a vaccine leak test and did not find any issues including at the vvt seals I also went to the local parts store to see if we could get a test on the fuel pressure but I think there tester was bad because we could not get it to register at all even when it was squirting everywhere. I will call a local shop and see if they can get me a number on Monday. I did notice that it takes a second for the fuel pressure to build on after sitting for a while. That makes me suspicious of the regulator. Is there a chance I got a defective one?

 

if you have a Harbor freight - they carry them for $32

https://www.harborfreight.com/fuel-i...ter-58760.html

 

Yes, it makes perfect sense. I feel your pain. It's expected but still an unwelcome surprise when it happens.
First, you should be dragged behind the shed and flogged with a length of fuel hose for using an O'Reilly part. Just kidding, but you really, really shouldn't use parts store stuff on your Jag. My best guess is that you have a bum fuel pump, based on the above. The pressure will fall over time when the engine is off. But it should be measured in hours and days, not minutes. For whatever that's worth. It's possible you have a bad regulator. I don't think it would cause pressure bleed-down but I suppose it could not allow sufficient pressure to the injectors. That's a bit of a stretch, but regulators are easier to change than fuel pumps. What brand did you use? You can check the diaphragm by applying vacuum to the nipple. (One of MY favorite pastimes, but I digress). Maybe swap out the regulator first, just in case? Regardless, first step is to get a pressure reading and go from there.

 

Jaguar issued a TECH TIP a few decades ago for this fault.
If a vacuum leak cannot be found, A MAFS can fail and cause issues.The HARD REST is the key to clear all fuel trims.
Monitor fuel trims and compare old vs new MAFS.

 

I was finally able to get a fuel pressure result looks like it stabilizes at 40 psi here is a video

 

That doesn't look right. The pressure should be more or less instantaneous from key turn. It shouldn't take several seconds and revving the car to come up to 40.

 

that was with it not running and us manually turning on the fuel pump via a relay bypass. The fact it took so long to build up pressure may be a clue. Anyways I tried a different maf sensor and same issue so I think that is ruled out. I may be buying a parts car that is in better shape than my car this week if I do I will be swapping my engine and trans over to that car�. In the mean time am I still looking at a weak fuel pump?

 

From what you've posted so far, it sure looks like it. I've measured pressure on my other cars and the jump from roughly zero to full pressure was only a second or two. There are only two reasons - bad regulator or bad pump. What brand regulator did you use for replacement? The pump?

 

so while replacing the pump I may have found something but I need someone to confirm. Years ago I damaged the pipes coming out of the fuel tank and to fix it we got a straight piece of quick connect repair pipe and fuel line. It works but thankfully no one can see the fix� anyways I had a thought that what if the lines got switched like pressure is going to return side of the injector rail and so on. So while I have it apart I�m double checking that. Right now the pressure side is going to the quick connect on the top of the rail not the one on bottom below the throttle body. Looking at that it appears the regulator would have to open full before any fuel pressurizes the system. I think it should be opposite where the regulator releases excess fuel pressure. Can anyone confirm this? FYI I�m not sure what regulator brand but I bought this https://www.highflowfuel.com/genuine-walbro-ti-gss342-255lph-fuel-pump-for-jaguar-xk8-all-1996-2002/?sku=WAL-GSS342G3-766-0098&gad_source=1&gclid=CjwKCAjwgfm3BhBeEiwAFfxrG2 gXjfN1uj_uDcoV8DT4w_k9iar1TJCWvdVMfliEXqsJ5NULit4f 0xoC4UQQAvD_BwE.

 

Well I have confirmed the issue was the send and return lines were swapped during a previous repair. Once that was resolved the error went away.

 

So the fuel was coming in the back door and exiting out the front. No wonder the pressure gauge was wonky! Congrats on the fix!!