I borrowed a fuel pressure gauge from a friend and find his fittings do not work for the Jag XK8 rail system. My car is a 2001 XK8 with 50 K.

Know where I can get a adaptor to fit that rail?

What is the fuel pressure that it should read with a running engine or with just the key on?

I am trying to eliminate the fuel filter and fuel pump as the problem from my recent check engine light and P0174 code.

 

Hard to believe it won't fit, that's a standard fitting. Pressure should be 40.

 

I bought a relatively inexpensive fuel injection pressure tester from Harbor Freight that has the adapter to fit the fuel rail Schrader valve.

 

The code 0174 most likely indicates a vacuum leak after the MAF sensor. The most common is the corrugated section of the intake piping. Also, the part load breather will create the same code assuming you have an XK8. If you have an XKR a leak at the EGR valve would also cause the 0174.

It would be most helpful if you added the model and year to your signature so it would always be there and you want have to worry about forgetting to put it in your post.

If you know you have more than 30,000 miles on the fuel filter then it's time to replace it anyway.

 

Fuel pressure should be around 35-40 psi with ignition on. Idle should be around 45 or so, and when you rev it it should go up to about 50-55 psi.

 

Looks like a trip to Harbor Freight is in order. I love that place. Will get a Fuel Injection Pressure Tester that fits the Schrader Valve.

Thanks for all the assistance it sure is appreciated.

 

Regarding Fuel pressure, Mine reads 48# at idle and maintains 48#s with slight increase in engine speed. The Gauge is from Summitt racing and liquid filled. I have used it on other EFI cars and readings have been accurate. Not much to offer on this problem, but was unable to locate pressure guidelines with google searches. I've seen suggestions from 40# to 58#. Hopefully this will help others.

 

Mine is 40# with the Harbor Freight. My local expert reduced it to that while checking the CAN for me, said it was the correct value and would improve fuel economy, which it has not.

 

Got the Harbor Freight fuel injector tester today and my pressure seems to be within specs. 35+ with the key on and 40+ running.

Still might change the filter and run out the tank of gas with the seafoam mixed in before I beg our membership for more ideas re my P0174 codes on bank 1 & 2.

Car is a 2001 xk8 with 50 K on the clock.

 

Had to laugh when I put the pressure gauge on the windshield so I could see it clearly when seated in the car. Got nice pressure then gas sprayed all over the windshield. Fixed that connection with Teflon tape and fired her up for the running pressure test.

Got good numbers but then the other two connection of the hose to the hose and to the valve started spraying fuel all over the throttle body and other areas. Shut it down, cleaned it up and realized just the pressure from the fuel pump has caused the two thumb tightened fittings to lose their seal.

So if you get the Harbor Freight equipment make sure your connections are tight before running your engine. Big fire hazard of course.

I have driven a good 20+ miles on the highway at 60+ mph to test the recent fix and no codes so far. I did not do any spirited acceleration just drove normally. Goal was to run out that gas in the tank that has the seafoam cleaner mixed in.

Keeping my fingers crossed.

 

Had the same experience with the Harbor Freight pressure testing kit. Copious amounts of Teflon tape and over-tightening the fittings reduced the leak to a slight drip, but still enough to make me nervous. Guessing that the tolerances on those fittings are a bit broad.

 

My 2004 XKR Fuel Pressure as read electronically from OBD reader shows 55 PSI at start and idol and will stay in that area only increasing slightly on heavy acceleration. It will spike at 70 if the key starts the pump 2X prior to starting then go quickly back to mid 50s pretty much throughout. These numbers seem high from whst I read. Also the pressure holds very firm for about 5 minutes then it drops to about 10 - 12 lbs. Your thoughts?

 

Even if the price of these pumps seems to have dropped quite dramatically in the last couple of months (check eBay), the idea was always to baby them along the way. The pop valve at the pump seems to play a critical role in pressure regulation and seems to benefit from a regular application of a quality fuel injector cleaner. Most of us go with techron, in the concentration detailed on the bottle, say, once every oil change.

To my knowledge, the fuel rail temp sensor can tell the ECU when the car has been sitting hot, and temporarily increase the fuel pressure on the next restart to avoid vapor lock.

 

My fuel rail was holding 35 psi when running , but as soon as I shut it off it would dump to 0psi.
Installed a check valve in the fuel lin, incase the fuel pump was having issues. But that didn't help.
Decided to change the fuel pressure regulator cause that was the only thing left. Could not believe the fuel injectors would loose pressure that fast.
Pulled the regulator and this is what I found.





No wonder fuel rail would not hold pressure