engine starts and idles fine, when you start to accelerate it starts to jump and sputter and wont gain any speed. When you let up on the accelerator it goes back to idle just fine. this came on all at once, no warning signs, code p0087 says low fuel rail pressure.
some things I read says it could be fuel pump, but would it still start and stay running ? could it be the filter ?
HELP HELP HELP
Thanks

 

You should go ahead and change the filter but I would plan to get the fuel pump replaced.
.
.
.

 

i will do that.
what about the fuel pressure regulator, because I did get two codes p0087 low fuel rail pressure and p0088 high fuel rail pressure?

 

If it is the fuel pump,remember an electrical fuel pump is available to put into your housing to save you some cash.

 

What reading do you get for Fuel Rail Pressure?

 

You could have a bad fuel pressure sensor but that does NOT match your symptoms.
Your lucky because everything you posted points directly to the fuel pump being bad. The car idles then falls flat when you give it the gas. This is EXACTLY what a weak fuel pump would do. You also have a code pointing to low or at least varying fuel pressure.

Do what your troubleshooting is telling you and then see what happens.
If your really worried hook up a mechanical fuel pressure tester and see what your actually getting for fuel pressure.
.
.
.

 

Many readers will tell you the fuel rail pressure while running.

 

Right but you want an independent method of measuring fuel pressure. That's why a mechanical gauge is useful here.
.
.
.

 

In my opinion (for what it is worth) I agree with both of the above posts. The symptoms are better matched by a failing Fuel Pump. When my Fuel Rail Pressure Sensor failed my car was difficult to start?
However, when it did start, I also got a very different FPRS pressure reading on the cheap OBD11 reader I had at that time. I changed the FPRS for a Ford unit and my problem went away.
Checking whether or not the Fuel Rail Pressure Sensor reading has changed from 'normal' seems (to me) like a good (and cheap) way to simply dismiss that possibility and concentrate on something else?

 

So I went looking for the valve to test the fuel pressure and could not locate it. So I started tapping on things , what looks like a pressure regulator, and the pressure sensor....
Well now it is running just fine, its not throwing any codes ?????

 

Check the plastic vacuum pipe that goes from the TB/Inlet to the Fuel Rail Regulator....They can become brittle and leak?

 

Hmm. Tapping on things. Sounds like yo have the touch. Want to swing by here? I have few candidates for "tapping". LOL! I hope the issue WAS a regulator or just a fluke, and doesn't return.

I can see it now... The tapping getting progressively more intense until your tapping with a sledge. So, is it continuing to run well?

 

I think you have the 4.2L V-8?
On the V-8 the test port is on the passenger side towards the rear of the engine. I have also seen it on the drivers side at the front of the engine.
When I had a problem with fuel pressure on my 2005 S Type R it turned out to be the fuel pressure sensor.
It looks like this;




It does look like Jaguar dropped the test port at some point too. So if you can't find the test port all you can do is use the scanner read out.
.
.
.

 

That's usually what it comes to , but mechanical and computer things know that the bigger hammer is coming, so they will most times straighten out. haha

 

I can confirm that my 2005 XJ8L does not have a test port. My Fuel Rail Pressure Sensor failed and its failure was obvious by way of a basic OBD11 wireless code reader which showed that the ECU was setting the FRP sensor at the maximum reading (which was much higher than any previous readings)?
It may also be worth me mentioning that its failure made starting my car difficult and poor running once started, but (as stated by Clubairth1 earlier) your symptoms do sound more like Fuel Pump?
Anyhow, as I said earlier, checking the FRPS reading with a cheap OBD reader seems like a good way to eliminate your FRPS as a cause?

 

on 4.2 NA 2006 XJ8 what is normal fuel pressure at idle ? thank You Ed

 

I would guess about 55psi?