I wanted to hook up an external fuel pressure gauge and according to JTIS there is supposed to be what they call a Fuel Pressure Relief Valve, known to the rest of the universe as a schrader valve.

From the description, it should be on the left side, near the front of the fuel rail, between the pump line and the cross over to the other side.

Thing is, I don't seem to have one.


I've seen it in pictures of other 4.2L cars, such as Maxwdg's:
https://www.jaguarforums.com/forum/a...noo-before-jpg



So, where is this thing? Surely they would not make a fuel rail without some kind of access to measure and relieve pressure.

 

Wow! What a pain in the a**!

That schrader valve was in the same place on my 2001 XJR as you see in that pic of my 2003 XKR.

Ummm, I don't know what to say. The replacement fuel rail and injectors that I bought off Ebay (just in case I needed it) has the valve in that place also.

I suppose you have looked up and down the rail on both sides of the engine, right?

This is no help, but I can't think of a way to easily check the fuel pressure at the injectors without one of those valves.

Side note: I'm glad I didn't need that salvaged rail, because as it turns out, the rail I bought was misrepresented as being for a 2006 XKR. The one I received was for XK (Non S/C) car of unknown year - I was pissed 'cause the injectors were for a lo-po car too! Nothing I could readily use. Oh well - it was only 53 bucks.

 

This would be a pain in the butt to do, but if you absolutely DO NOT have a schrader valve on those rails, you COULD remove the sensor on the rear of bank one rail and make up a short male-female section with a schrader valve on it that screws into the back of that rail and the sensor could be put back onto the new short section.

Another (much easier and probs cheaper) Idea: Go to the parts store and using "Doorman" fuel system (Ford style quick connectors) and hi-pressure fuel line and clamps - make up a short segment of line that has a "tee" fitting in it for a guage and temporarily put it line where the OEM fuel connector attaches to the fuel rail (your thumb is pointing at it in your picture.)

Hey, it may not be elegant, but you will be able to check the fuel pressure!

 

I looked as much as I could without taking the charge coolers off. And if the valve is under the intercooler somewhere then it might as well not be there because who could ever use it!

I'm really at a loss to explain this, unless the rail was replaced at some point with a knock off that didn't have all the components.

 

Hope you filed a "not as advertised" complaint ... preferably at paypal rather than ebay. Even if you only get back part of the money, the seller gets a black mark and might even eventually learn the intended lesson. For charge cards, there is always the magic chargeback.

 

@ccfulton

What's that hose crossing the valvecover attaching to the fuel rail?

It attaches to the fuel rail at the exact place where the schrader should be. Maybe someone plumbed something else into the system using the schrader port.

 

The hose that runs off to the lower right corner of the pic is the main fuel line from the pump.

The only other connection is partially visible, directly above the forward most valve cover bolt, and is the hose connecting to the right side.

 

There's an app for Android phones called "Torque". It interfaces with the car through an OBDII device that connects to the phone via bluetooth. You can read your fuel pressure with that app. In fact, you can read all sorts of interesting data such as manifold pressure, coolant temperature, etc... The OBDII device is about $50 and the app is only $5. Plus there's a free version.

 

yah, you should have fuel pressure readings using an OBD like the ghost of Rev mentioned (gone, but not forgotten) on the 03 MY cars since we got a fancy sensor that the earlier cars didn't.

 

True, I can read it with Autoenginuity, but what I'd like to see is if it is bleeding down when the car is not on.

I've had the pump replaced twice now for the typical slow start problem and it has come back yet again... sort of. The long crank does happen but isn't consistent like it was before so I was wanting to see the pressure after a long sit time and also how it behaves when toggling the key.

 

I think the pressure drops pretty quickly even if the check valve is working properly. The valve doesn't hold the pressure, it just keeps the fuel up at the fuel rail. That way when you turn the key, the fuel pump doesn't have to pump air out of the fuel line before the engine starts.

On old cars with carburetors it wasn't an issue because there was always some fuel in the bowl unless the car had been sitting for several weeks. The engine would suck in that fuel first, and by the time the bowl was getting low, fuel from the tank was already being pumped up to the bowl to refill it. With an injected car, however, the fuel in the fuel rail absorbs the heat from the engine after the engine shuts down. That causes it to expand, pushing fuel back into the tank. Then when it cools, it leaves an air gap up at the rail. Plus, since the rail is higher than the tank, it would just gradually drain back into the tank over time without a check-valve. The check valve appears to make a tight enough seal to prevent the fuel from draining back, but it's not so tight that it prevents the pressure from bleeding off.

My OBDII tool would work with the key in the accessory position, and it would show the fuel pressure to be 0 psi. As soon as I would turn on the key, the pressure would climb because the pump starts running to build the pressure needed.

 

So, what I need to do to fix the problem is replace all that fuel injection business with a carburetor?

My first pump failure (https://www.jaguarforums.com/forum/x...nalysis-80018/) was actually the little pressure bypass rather than the check valve.

That time it was stuck pretty well open, so let the fuel drain back quickly, but this round it takes some sit time and is less consistent, which has me wondering if that pressure relief is sticky or something.

I'll try position I vs II. I was thinking it had to be in position II to read the pressure.

 

I am not doubting Sam at all, but I will say that for me, on my 2004, I could never get the readings from my OBD unless the engine is running. Maybe it's just me, but i am not convinced that an accurate fuel pressure reading at rest can be made without a mechanical gauge on the shraeder valve.

My Jaguar mechanic has consistently been saying he sees the pressure drop with the mechanical gauge with the bad pumps (check valves) and after pump replacement the pressure maintains...I don't know how true this is, just conveying what he tells me.

Also ccfulton, my most recently replaced fuel pump that was bad exhibited similar behavior, which for me, was the first time any of my pumps did this. Basically, all replacement pumps worked fine until one day out of the blue I had long crank times, and once I had long crank times once, I had them every time, not intermittent. The most recent pump that was replaced however was like yours now where it was fine when installed, then some time later, out of the blue one day I had 1 long crank time, then ok the next several starts, then another long crank time several stars later, then a few more starts were ok, and gradually it became more frequent until all the time again with long crank times. I thought is was strange that this was the only pump out of the five replacements that exhibited this behavior. But alas, as you know, it was confirmed and the pump assy was replaced again. BTW, since then, I have been running ethanol free fuel, and so far all is ok (I hope I didn't jinx myself). Honestly, running ethanol free fuel doesn't seem like a long term or permanent solution, but I am giving it a try until I am convinced all is ok (if I can ever gain back that confidence - not sure about that).

 

The thread has taken a bit of a detour from my original intent, which was simply to ask if anyone out there knew of an alternate location for the shader valve or had ever seen a rail without one.

It is sounding like the answer is no to both of those.

Guess I'm just that lucky.

 

I tried your suggestion but can't connect to the car in position 1, only in position 2. What's interesting though, is that once connected and monitoring the fuel pressure, I can toggle back and forth between position 1 and 2 without losing the connection. When I switch to position 1 the reading immediately goes to zero, I assume because the voltage to the sensor is cut off.

Last night, when I tried this the first time, (car had been sitting a couple of days) the pump ran a few seconds and the pressure didn't come up to more than about 4psi. Long crank. Fuel pressure increased progressively as it was cranking away and then stumbled to life.

I shut it off and the pressure stayed high and only decayed very slowly. I guess the check valve closed and sealed a little better than it usually does in this case?

The pump wouldn't come on and run when switching to position 2 while the pressure was above about 55psi, which I thought interesting.

Once the pressure did decay to less than the threshold, the pump would run when switching to position 2 and it must have popped the valve loose or something, because after that, the pressure would decay in about 10 seconds or so.

This sounds like the behavior the Rev describes as "normal". After that, there were no long crank problems.

This morning I repeated the experiment and saw the same behavior with the 10s pressure drop off. Car started like normal.

So at this point I'm not sure what conclusion to draw. The behavior of the valve doesn't seem to correlate with the long cranking. I guess I will just have to wait and see if the failure gets to be more consistent like SteveJacks did.

 

Usually the pressure drop-off lets the fuel boil with a hot engine, which will cause a longer start. So that could explain that you don't experience a tough start with a cold engine and pressure drop-off.

 

Is it your observation that the pressure should hold once it is up to that 70psi or is the fall off the normal behavior?

 

It can drop, even to zero, that in itself is no issue, as long as some pressure remains for at least 1 to 2 hours until the engine is cooled enough to avoid the boiling.

 

Just to try and tidy up the situation regarding the lack of a schraeder valve on the fuel line; the following is an extract from the MY2004 Update for the X Type, but is almost certainly applicable to all models;

The vehicle has a new fuel system designed to meet USA
Federal LEV 2 emissions requirements. Parts affected are:
• Under floor fuel lines.
• Fuel tank assembly.
• Fuel filler pipe.
• Carbon canister.
• Fuel filler cap.

Service Port

In order to further reduce emissions, the fuel rail ’schraeder’
valve is deleted. Should a service port be needed, a new
service special tool will be available to fit between the fuel

rail and the fuel feed line connection.

Neither my X Type nor XK8 have schraeder valves that confirms the story for me! I depend on AutoEnginuity.

 

Very good to know, thank you for the information!