Figure that since it's a no-code, with symptoms that look like other things (injector, spark etc) I'd lay it out for those who might care.

'07 4.2 NA. The FPS is on the end of your fuel rail on NA 4.2 vehicles. Not sure where it is relative to 5.0 fuel rails -- the 5.0 code list mentioned it, but couldn't find a pic in the 5.0 manual.

When a FPS fails, it usually pulls a code. Mine didn't, and failed slowly for awhile. Symptoms were pretty consistent, and can be seen on a JLR compatible code reader or SDD. Can make you feel you have a leaking injector or bad coil.

• A few soft misfires* on random cylinders at regular RPM, increasing over time.
• Lots of soft misfires at 4K+ rpm, all cylinders, some more than others. Couple of actual backfires at 4K, as well. A 4-5K rpm for 30 seconds caught a lot of misfires.
• On mine, LTFT's drifted towards the positive, meaning the ECU was reducing fuel in the mixture. After replacement, they drifted back to normal range.
• Fuel use on highway trips dropped from 28-30 to 24-26, consistent with the LTFT situation. Also seemed low around town, but my lead foot was a poor measuring tool.
• Slow start when heat soaked -- starts, but struggles for a moment. Clearly different that the quick normal start.
• Idles rough, with a +- 20-30 rpm range of variation. Feels like a failing motor mount.
• One more oddity. Two separate readers, one SDD, read 38 psi (OK), but 80 volts (!) on both the old and new FPS. No idea why.

I replaced mine for $55 from FCP Euro (lifetime warranty), using a Eurospare unit. There's lots out there that's cheaper, but FCP guarantees its product is what it claims to be.

Very easy fix: two bolts and about 20 min, with easy access. BUT! be very careful of the vacuum hose connection on the side. The thin grey vacuum hose connected to the FPS is really fragile. It can be fixed/replaced with the proper size vacuum hose slipped over the broken grey vacuum pipe.

Idle was instantly smoother, acceleration also smoother, and LTFT's readjusted back towards zero over a 10 mile drive.

Panthera


* A soft misfire is one that's detected and recorded on the "non-continuous monitors" section of your reader. Lots of them will eventually trigger an actual misfire code, but it takes awhile.

 

I changed mine a few weeks ago. As you say, a 10 minute job. It's not actually at the end of the rail. That's the Fuel Temperature Sensor.
The car kept showing the check engine code and, after a while, going into Restricted Performance mode. Clearing the codes sorted it for few days but then the cycle started again. The new FPS has sorted it.

Richard

 

Thanks. Should have been more specific. Top of the end of the forward right hand (facing forward) fuel rail.

Question for those who might know: I noticed that the fuel rail pressure sensor shows a consistent 38 PSI, whereas the fuel pump pressure sensor says the system is at 55-60 psi. Doesn't pascal's law say that all points in a fluid system should be at the same pressure? I don't know of any pressure reducing hardware in the fuel system from fuel pump to injector.

 

According to the manwell:

Each fuel rail maintains a fuel pressure of typically 4.5bar (65 psi), however, this pressure will vary
depending on engine requirements; lower at idle, higher at full load. Four fuel injectors are installed
in each cylinder head and are connected to the fuel rail. 'O' ring seals are used to seal the injectors to
the fuel rails.

Maybe the fuel rail sensor is whooped? I don't see a fuel pump pressure sensor in the manwell - unless it named differently.

 

Below is a data capture from my4.2 NA XK. System fuel pump pressure vs. fuel used. ***the flat spot is a bluetooth glitch -- ignore it.**

As you can see fuel pressure varies in 55-65 psi range.

At the same time (lower pic, captured from SDD), the fuel pressure sensor is steady at 38 psi.

Both the old and new FPS recorded 38 psi, at a constant level over time.

Shouldn't the entire fuel rail be at the fuel pump pressure?

 

It looks like the blue graph is doing exactly what the manual says (I'm guessing that's the fuel rail pressure) - varying with driving conditions. I can't say why the SDD is not showing correctly, maybe there is a scaling error in the software. Maybe someone else could check their SDD pressure?

Shouldn't the entire fuel rail be at the fuel pump pressure?

Should be.

Both the old and new FPS recorded 38 psi, at a constant level over time.

Something isn't right there for sure, but what? I would think the SDD. If the ECM saw a flat line from the fuel rail pressure I doubt the car would perform right.

 

Since it's mentioned in the OP's first post, the fuel pressure sensor for the 5.0 Litre AJ133 and AJ133S is on the back of the Bank 1 high pressure fuel line. There is no fuel pressure sensor for Bank 2, so if there is a leaking HP injector on Bank 2 of the AJ133/AJ133S, possible misfire(s) can be detected (P0302, P0304, P0306, P0309, and P0300/P1316), but may be caused by only one sticking injector.

 

That's interesting. My Fuel Pressure Sensor also measured a constant 38psi both before and after the change of sensor. I was expecting this to be at around 55psi from research I had done before changing the sensor so I decided that the 38psi is a gauge pressure reading as the sensor is open to atmosphere through the intake vacuum connector. If you add 15 to this you get an absolute reading of 53psi which is perhaps correct for a line which is not open to the atmosphere.

I don't know whether this is correct but, either way, the engine now runs properly.

Richard

 

Thanks -- I wondered where it was. If it comes to mind in your experience, is the FPS on the NA 4.2 supposed to stay at 38 psi, or should it move with fuel rail pressure variations from the fuel pump?

 

Just an additional comment on the 80V thing: I metered the FPS lead and got 4.99 VDC on it (SDD had a note that it should be 0-5VDC). So, somewhere in the ECU software is a mistaken display value, since I read 80 V on two readers (SDD and Autel), but the actual meters correctly.

 

I also get the same 80V reading from my iCarSoft Pro. Obviously, it's nonsense so I ignored it.

Richard

 

The fuel pressure is controlled by the ECM/PCM based on engine load, so it does change based on engine speed and load.

 

Conclusion. Fixed. A few weeks later. The odd symptoms mentioned in the first post have vanished, so I'm concluding the new FPS made a difference. LTFT's are now minus 1-3%, well within spec. Idle is stable within 10 rpm of spec. Soft misfires across multiple cylinders have largely vanished, now concentrated on Cyl 5 in the <10 per drive cycle -- so will look closely there for further issues. Heat-soaked starts are no longer an issue.

 

EDIT: One final note. After installing the new unit, I began to smell gasoline vapor coming through the vents. Went right to the new part, figuring either defective or a poor seal to atmosphere at the pressurized rail interface. I measured the gaskets on the FPS nozzle and since it was a easy test, installed replacement 7.65 x 1.78 vitron orings. The new gaskets had a .5mm or so tighter seal. Fixed the problem. I guess I'd suggest that parts for old cars can sit in inventory for a long time and orings can degrade. Anyway, I think you should expect some resistance when you insert the new part into the fuel rail. If you don't have to twist it a bit to get it into the rail, be aware of a possible fuel smell and replace the orings with tighter ones if you do. Cheers.

 

im so happy I found your post about the problems you were having with your car. I’ve had the exact same problem and I’ve been dealing with it for a couple months everyone thinks my scanner is reading wrong but I got a 80v reading from the FRP sensor same as yours as well as no active codes on the dash. I ended up pulling a FRP from the junkyard that had the same part numbers on my car plugged it in and still had the same readings. I also just recently bought one from o reilys which didn’t work ethier gave me the same readings I also unplugged the connector from the sensor and the readings stayed the same I also want to mention that the fuel pressure stays at 265KPA even while driving like it’s stuck do you think I should buy the same one you got and attempt that or do you have anything helpful that might help me I would be very appreciative.