Fuel pressure.
#1
03-16-2018, 05:25 PM
Fuel pressure.
Hi,
I recently acquired a lovely 87,000 mile Aegean blue X type 3.0 manual with Dove grey interior and have been slowly working my way through the car carrying out service to engine, gearbox, transfer case, and differential, braking system, plus any other niggles that showed up along the way.
To date, the only horror I've encountered was when I drained the transfer case and only 50ml of black oil dropped out. This was from a hole I drilled into the bottom of the case. I promptly tapped this hole and injected 600ml of Syntrax before fitting a sealing plug. With no apparent leaks I was confused until I read on this fine forum that the oil can migrate along the splines and into the prop shaft rubber boot. My next job was to remove the prop and reseal the splines and threads with sealant. T/C is now leak free!
I do have one problem that is proving tricky to diagnose...The car starts and runs almost perfectly, except for a very minor misfire at low revs and fairly hard throttle. Once the revs pass 2k the misfire is gone and the engine will happily rev on all cylinders. To date I have replaced the spark plugs with new NGK'R', upper inlet manifold gaskets, checked for vacuum leaks with brake cleaner(found a very minor leak on one of the push fit pipes which is now fixed), replaced brake booster NRV pipe, FPR pipe, and PCV pipe. Spraying brake cleaner on the other pipe fittings had no effect on idle or STFT so have ruled out any further vacuum leaks. No fault codes are stored and no EML on.
STFT and LTFT are both around 0. Bank 2 LTFT may be slightly higher at 2.
One thing is puzzling though..fuel pressure measures 55 psi on ignition which is great. On starting the engine it remains at 55psi. Removing and plugging the (new) vacuum hose from manifold to FPR has no effect on the pressure. I would expect the fuel pressure to be less when the engine is started due to manifold vacuum at idle.
Vacuum appears to have no effect on the fuel pressure. Fuel pressure is measured with ELM and Torque pro app.
So, enough of my wittering. Firstly, is my fuel pressure behaving normally? Secondly, if it isn't, could this be the cause of my infrequent misfire problem?
Thanks for reading.
I recently acquired a lovely 87,000 mile Aegean blue X type 3.0 manual with Dove grey interior and have been slowly working my way through the car carrying out service to engine, gearbox, transfer case, and differential, braking system, plus any other niggles that showed up along the way.
To date, the only horror I've encountered was when I drained the transfer case and only 50ml of black oil dropped out. This was from a hole I drilled into the bottom of the case. I promptly tapped this hole and injected 600ml of Syntrax before fitting a sealing plug. With no apparent leaks I was confused until I read on this fine forum that the oil can migrate along the splines and into the prop shaft rubber boot. My next job was to remove the prop and reseal the splines and threads with sealant. T/C is now leak free!
I do have one problem that is proving tricky to diagnose...The car starts and runs almost perfectly, except for a very minor misfire at low revs and fairly hard throttle. Once the revs pass 2k the misfire is gone and the engine will happily rev on all cylinders. To date I have replaced the spark plugs with new NGK'R', upper inlet manifold gaskets, checked for vacuum leaks with brake cleaner(found a very minor leak on one of the push fit pipes which is now fixed), replaced brake booster NRV pipe, FPR pipe, and PCV pipe. Spraying brake cleaner on the other pipe fittings had no effect on idle or STFT so have ruled out any further vacuum leaks. No fault codes are stored and no EML on.
STFT and LTFT are both around 0. Bank 2 LTFT may be slightly higher at 2.
One thing is puzzling though..fuel pressure measures 55 psi on ignition which is great. On starting the engine it remains at 55psi. Removing and plugging the (new) vacuum hose from manifold to FPR has no effect on the pressure. I would expect the fuel pressure to be less when the engine is started due to manifold vacuum at idle.
Vacuum appears to have no effect on the fuel pressure. Fuel pressure is measured with ELM and Torque pro app.
So, enough of my wittering. Firstly, is my fuel pressure behaving normally? Secondly, if it isn't, could this be the cause of my infrequent misfire problem?
Thanks for reading.
#2
03-17-2018, 02:10 AM
Veteran member
Join Date: May 2008
Location: Great Mills, MD
Posts: 14,220
Likes: 0
Received 3,825 Likes
on
3,144 Posts
Bwant, you do have an issue. You have a good fuel pressure with the engine off, but it should drop about 10 psi when the engine is started (ie, to the 40-50 psi range). So, this is telling me that you either have a bad vacuum hose going to the fuel pressure regulator or your fuel pressure regulator is stuck and it just happens to be maintaining 55 psi.
Having the fuel pressure too high can cause too much fuel to be introduced, leading to a rich condition. This could be interpreted as a misfire condition.
Having the fuel pressure too high can cause too much fuel to be introduced, leading to a rich condition. This could be interpreted as a misfire condition.
#3
03-17-2018, 03:52 AM
Thanks Thermo.
You've confirmed my suspicions that the sensor is stuck. I had previously Googled in an attempt to find something from Jaguar regarding the operation of this part but found nothing. I wondered whether the pressure stayed high under certain circumstances, and dropped down when fully warmed up, say?
It looks like I'm going to need part number AJ87977 - fuel rail pressure sensor/transducer.
The hose from this part to the inlet manifold is brand new so I can rule that out.
You've confirmed my suspicions that the sensor is stuck. I had previously Googled in an attempt to find something from Jaguar regarding the operation of this part but found nothing. I wondered whether the pressure stayed high under certain circumstances, and dropped down when fully warmed up, say?
It looks like I'm going to need part number AJ87977 - fuel rail pressure sensor/transducer.
The hose from this part to the inlet manifold is brand new so I can rule that out.
#4
03-17-2018, 09:06 AM
While I wait for the new part, I'm looking around the forum gathering info.
I read a thread by Neo17 with a misfire problem on his X type. He had actually posted a screenshot of his Torque app with his fuel pressure at idle, and at medium revs.
Interestingly, his fuel pressure at idle is the same as mine, ie. not 45 psi.
Coincidence? Maybe this is a common problem.
I read a thread by Neo17 with a misfire problem on his X type. He had actually posted a screenshot of his Torque app with his fuel pressure at idle, and at medium revs.
Interestingly, his fuel pressure at idle is the same as mine, ie. not 45 psi.
Coincidence? Maybe this is a common problem.
#5
03-17-2018, 02:22 PM
Veteran member
Join Date: May 2008
Location: Great Mills, MD
Posts: 14,220
Likes: 0
Received 3,825 Likes
on
3,144 Posts
Bwant, here is the trick. The computer can figure out the rate of fuel to inject only if it knows the difference in pressure across the fuel injector. So, with the engine off, the intake is at atmospheric pressure. So, it knows to add 55 psi to that number. But, when you start the engine, the area where the fuel injector admits fuel too drops in pressure (down to around 20 inches of vacuum, or -10 psi). So, adding 55 psi to -10 psi, you end up with 45 psi (hence why they say you should see 40-50 psi with the engine running). Now, if you get on the gas, the throttle has to open up. This brings the intake vacuum closer to atmospheric, so, yes, the fuel rail will gain a few psi to maintain the differential pressure across the fuel injector constant.
In your case, because the fuel rail is maintaining itself at 55 psi and you start the engine, you end up with a 65 psi difference across the fuel injector. This results in more fuel being added to the engine for a given amount of time the injector is open. This causes the car to run rich, giving you engine codes which can be seen as either a rich condition or a misfire. It is all a matter of whether the computer is seeing all the cylinders with a rich condition or only a majority of them. Having the fuel rail pressure only slightly higher, I can see where the computer would interpret it more as a misfire than a "rich condition".
In your case, because the fuel rail is maintaining itself at 55 psi and you start the engine, you end up with a 65 psi difference across the fuel injector. This results in more fuel being added to the engine for a given amount of time the injector is open. This causes the car to run rich, giving you engine codes which can be seen as either a rich condition or a misfire. It is all a matter of whether the computer is seeing all the cylinders with a rich condition or only a majority of them. Having the fuel rail pressure only slightly higher, I can see where the computer would interpret it more as a misfire than a "rich condition".
#6
03-17-2018, 02:47 PM
Thanks for that info Thermo. Wondering now if my Torque app is showing adjusted fuel pressure relative to the inlet vacuum and so I should measure the pressure from the valve with a stand alone gauge? It just might show 45ish at this point.
If I'm talking rubbish just give it to me straight. I can take it!
If I'm talking rubbish just give it to me straight. I can take it!
#7
03-17-2018, 03:47 PM
Mmm. Interesting. 
I've just been out and measured my fuel pressure using AutoEnginuity. In all conditions from just ignition on to engine running at different speeds inc idling, the fuel pressure never varies from 54-55 psi and I don't have a problem!!
I would suggest that the ECU knows Atmospheric Pressure, Absolute Manifold Pressure and Fuel Pressure and they enable it to calculate the necessary injector opening at a design (nominal) constant fuel pressure for all engine speeds and loads. Your problem lies elsewhere, though you've been pretty comprehensive in your work so far!
Though you've sprayed with brake cleaner, I think it might be time to use a smoke test to perhaps get to the fine detail. That will ensure a 100% test of the whole intake system that's difficult with a spray, but there's almost certainly a little leak in the background laughing at you!
PS Whereabouts in UK are you? Anywhere near Portsmouth/Southampton?
I've just been out and measured my fuel pressure using AutoEnginuity. In all conditions from just ignition on to engine running at different speeds inc idling, the fuel pressure never varies from 54-55 psi and I don't have a problem!!I would suggest that the ECU knows Atmospheric Pressure, Absolute Manifold Pressure and Fuel Pressure and they enable it to calculate the necessary injector opening at a design (nominal) constant fuel pressure for all engine speeds and loads. Your problem lies elsewhere, though you've been pretty comprehensive in your work so far!
Though you've sprayed with brake cleaner, I think it might be time to use a smoke test to perhaps get to the fine detail. That will ensure a 100% test of the whole intake system that's difficult with a spray, but there's almost certainly a little leak in the background laughing at you!
PS Whereabouts in UK are you? Anywhere near Portsmouth/Southampton?
Last edited by astromorg; 03-17-2018 at 03:51 PM.
Trending Topics
#8
03-17-2018, 04:57 PM
Thanks for taking an interest Astromorg. My fuel pressure acts exactly like yours, even with the vacuum hose disconnected and plugged.
Heres the thing, I don't recall the car misfiring once with the old, original spark plugs in although I'd only driven it a few hundred miles since purchase. On removing the old plugs, I was happy to see them dirty and with enormous gaps somewhere near 2mm at a guess. The new plugs came in Jaguar boxes marked 'NGK'R' and were gapped correctly. The new, green upper inlet manifold gaskets were in perfect condition.
During the plug change, I inspected everything as I went along. Hoses, wiring, plugs etc. Nothing looked damaged or broken hence my suspicion of the fuel system. Maybe I have missed something whilst refitting the inlet manifold? Since the misfire, I have changed several hoses as mentioned earlier with no change.
Looks like I'll be removing the manifold again to recheck under there. In the meantime, I'll buy a fat cigar and blow smoke into it. Which is the best hose to blow smoke into? I'm struggling to blame an air leak at this stage as it runs beautifully on idle. Even loosening the oil filler cap affects the idle so if it is a leak,it must be minuscule.
Heres the thing, I don't recall the car misfiring once with the old, original spark plugs in although I'd only driven it a few hundred miles since purchase. On removing the old plugs, I was happy to see them dirty and with enormous gaps somewhere near 2mm at a guess. The new plugs came in Jaguar boxes marked 'NGK'R' and were gapped correctly. The new, green upper inlet manifold gaskets were in perfect condition.
During the plug change, I inspected everything as I went along. Hoses, wiring, plugs etc. Nothing looked damaged or broken hence my suspicion of the fuel system. Maybe I have missed something whilst refitting the inlet manifold? Since the misfire, I have changed several hoses as mentioned earlier with no change.
Looks like I'll be removing the manifold again to recheck under there. In the meantime, I'll buy a fat cigar and blow smoke into it. Which is the best hose to blow smoke into? I'm struggling to blame an air leak at this stage as it runs beautifully on idle. Even loosening the oil filler cap affects the idle so if it is a leak,it must be minuscule.
#9
03-17-2018, 05:35 PM
Now I'm taking a greater interest in your spark plugs! You say no more than NGK R that just means it's a resistor plug, which is correct, but which R plug?
The NGK site recommends TR6AP-13E for your engine. Is that what you've got?
When you were checking for leaks, did you check out the main air inlet trunking between the MAF and the throttle body for splits in the corregations?
The NGK site recommends TR6AP-13E for your engine. Is that what you've got?
When you were checking for leaks, did you check out the main air inlet trunking between the MAF and the throttle body for splits in the corregations?
Last edited by astromorg; 03-17-2018 at 05:41 PM.
#10
03-17-2018, 06:09 PM
Part number on the spark plug boxes - C2S46895. I'm 99% certain it had 'NGK'R' in blue on the plugs themselves.
I don't have the old ones now unfortunately. Do you think I have the wrong plug type in there?
Yes, I inspected the trunking and blasted it with brake cleaner whilst running. I had ruled this out also as when I removed the plastic pipe that goes into this part from the rear camshaft cover it immediately ran lumpy.
I don't have the old ones now unfortunately. Do you think I have the wrong plug type in there?
Yes, I inspected the trunking and blasted it with brake cleaner whilst running. I had ruled this out also as when I removed the plastic pipe that goes into this part from the rear camshaft cover it immediately ran lumpy.
#12
03-19-2018, 03:02 PM
#13
04-19-2018, 09:09 AM
Just a little update on this in case anyone ever wonders how it all turned out.
Well, she's running perfectly ever since I filled with 98 RON and Redex. I'm inclined to think I had some contaminated fuel in the tank as I've always been sceptical of Redex and its claims.
I'm back on 95 RON now and she still runs beautifully.
Thanks to all those who offered help with this.
Well, she's running perfectly ever since I filled with 98 RON and Redex. I'm inclined to think I had some contaminated fuel in the tank as I've always been sceptical of Redex and its claims.
I'm back on 95 RON now and she still runs beautifully.
Thanks to all those who offered help with this.
#14
11-21-2019, 07:01 PM
Bwant, you do have an issue. You have a good fuel pressure with the engine off, but it should drop about 10 psi when the engine is started (ie, to the 40-50 psi range). So, this is telling me that you either have a bad vacuum hose going to the fuel pressure regulator or your fuel pressure regulator is stuck and it just happens to be maintaining 55 psi.
Having the fuel pressure too high can cause too much fuel to be introduced, leading to a rich condition. This could be interpreted as a misfire condition.
Having the fuel pressure too high can cause too much fuel to be introduced, leading to a rich condition. This could be interpreted as a misfire condition.
Is it easy to replace that vacuum line to the fuel pressure regulator on a 05 xtype 3.0
#15
11-22-2019, 05:51 AM
Veteran member
Join Date: May 2008
Location: Great Mills, MD
Posts: 14,220
Likes: 0
Received 3,825 Likes
on
3,144 Posts
Falcon, I have not personally done this, but should not be too difficult. The big thing will be finding both ends of the line, disconnecting them and if you find that you have to run the line under a bunch of stuff, to tape a string to one end and pull the old line out and then use that string to run the new vacuum line back. Otherwise, you are most likely going to end up pulling the intake. Not difficult, but if you don't have to..........
Thread
Thread Starter
Forum
Replies
Last Post
iconic
XJ XJ6 / XJR6 ( X300 )
9
06-01-2016 11:44 AM
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)