Naturally aspirated 2004 XJ8 4.2 litre.
Check engine light and restricted performance message.
Codes P0171 and P0174.

Tried a home smoke test, no visible leaks anywhere - once feeding in to the breather for the left hand bank as it joins the air intake after the MAF and before the throttle body and once more with the air intake removed and lifting the throttle plate up a bit. I could see smoke if I disconnected the hose at the PCV valve sugegsting smoke was penetrating fairly well into the engine.
I have broken the nipple off the fuel rail pressure sensor, so I have temporarily folded that hose to block it off, and confirmed no change in fuel trims if I stick my finger over the open end of the hose. The open broken end on the fuel pressure sensor does not seem to impact anything. I assume this is just a fail safe means of controlling leaking fuel if the sensor fails by feeding it into the inlet? But does the fuel pressure at 54 psi seem too high?

The mass air flow seems really low (0.011 lb/s), does that suggest a MAF failure?

I have a new sensor coming tomorrow and a new PCV valve available later today.

Interesting to note the LTFTs are +20 and the STFTs are -20. What does that suggest?
The values do drop when the engine revs increase, so is that an air/vacuum leak, or a MAF failure?

I replaced 6 o-rings, two on PCV valve stem, 1 at each end of the two breather hoses, from the PCV valve and from the left hand cam cover. Oil filler is tight, dipstick seems fine and no smoke there. We did the coolant hoses and water pump etc. 5000 miles ago and that included new inlet gaskets, so not expecting a problem there.

Any help or suggestions would be appreciated.
This is my daughter's car, home for Spring Break and hoping to head back on Saturday, so time is short.

 

I’ve just been through this. In my case it was s leak which I found by making a stethoscope probe from a toy and a metal straw and went about listening for the leak. It was clearly audible in my case at an injector that I had not installed correctly and pinched the bottom o ring. My bad but the fact that I’ve been chasing this leak down for a few weeks and not found it, this method might help you if you do have a leak as a vacuum leak causing that error should make an audible hiss. Also check your VVT seals. If they are leaking oil they can also cause this type of error.

 

How much hissing is normal under the hood?
I can hear hissing around the PCV valve and the hose that then goes to the intake, but there is also the EGR valve close by and the fuel pressure sensor.
I can hear hissing all the way down the length of that hose, so it seems like I am hearing the air moving inside the hose, rather than a leak.

Spraying MAF cleaner and QD Electronics cleaner (both marked flammable) did not seem to bring about any change in fuel trims or engine revs.

I will go try listening again and maybe another smoke test.

 

When i was chasing these codes down on my 04.
Turned out to be those eight gaskets inside of the intake manifold.
Replaced the valley hose while i was there, easy job at that point.
Hoping that your problem is something else.
Good Luck to you

 

Zenderman prompted me to dig out the stethoscope.

Only conclusive is #1 injector was hissing, so I am off to parts store to see what they might have in the way of new injector seals/o-rings.

Fiddling with hoses etc has got the LTFTs down to 10 and 7, so something is still upsetting the left bank (all injectors sound hiss free on the other bank, so not that issue for them).

No hint of leaks in the eight gaskets, nor the recently replaced metal one piece below that.

 

How much hissing is too much I guess. The way I see it is that with the stethoscope it should be extremely loud and annoying. You should be able to hear air passing that’s for sure.

As far as the spray method is concerned, I think the electronics on these cars should be able to compensate the extra flammable gas and not cause any change in idle. Not sure our old school methods work so much any more…. I feel old lol

 

Interesting you’re getting a hiss from number 1. I’m guessing it’s a perished lower seal as top one would cause a fuel leak. In my case it was poor install of a new injector but it was definitely the cause. Probably worth changing all the seals “while you’re in there”. Fingers crossed it’s your issue. Dirty but simple job. Go carefully with the injector connectors and expect broken tabs. Very brittle with age… I’m on the hunt for new connectors. Seen some on eBay. For now they seem snug enough to get away with broken tabs.

 

All seems well after replacing the injector lower seals and the PCV valve.
I used Fel-Pro Fuel Injector O-Ring Set - ES70599 for a 2004 Ford Thunderbird from O'Reillys.
I changed out all 4 lower on bank 1.
Three tabs on the electrical sockets were already broken from previous swapping of injectors, but they have been like that for 2+ years and 20k+ miles, so I have given up worrying about them :-)
Hissing was definitely lower, but a short period of idling did not show much change from the 10 and 7 I had seen earlier for the LTFTs, so I swapped in a replacement PCV valve, (Beck/Arnley Crankcase Vent Valve - 0450401) and upon restarting the trims dropped and have been around zero ever since.
So not 100% sure the PCV valve made all the difference, were the trims going to drop anyway, but as the PCV valve is common to both banks and both were a little high, then maybe it was that.

I did swap the MAF with the one from our X-type, same part number, and that made no difference.
My daughter has the car now and has already done 125 miles no issue, I'll see it again tonight and check everything again then.

FYI, It does seem like the MAF and fuel pressures I saw are typical/acceptable.

 

Sounds like you’re sorted out. Great news. And thanks, I feel better about my broken tabs now…

 

Why did you think God - or was it the Devil? - invented Zip-ties?

Meanwhile... glad I bought a neat "kit' that had a supply of top seals, bottom seals, with their bespoke expanding cone, and the double-ended sizing tool.. before I started going at the injectors.

Two of four on one bank lifted out with the HP fuel rail. One of the other two required 375 slide hammer strokes, it's evil twin 550 strokes. And that was with a PB-laster overnight soak.

 

A necessary evil!!

I think I get away with a lot where I live. Warm and dry so my 19 year old XJ doesn't have a spot of rust or anything seized. Everything just unbolts and disconnects as it should. Heat in summer is the one to watch...

 

The Jaguar, not the zip ties...

LOL! The Barca family's Spain you are in. I'm so accustomed to a different climate, my love for ES is focused on the Costa Verde and Basque country where we've several times considered retiring!

How many Anglo-Americans do you know that would have asked Susana Seivane-Hoya to ship me the whole collection of her works? And carry it about in the Jaguar!

The Gaita Gallega surely prevents drowsiness at the wheel on long treks!

 

I had to look her up…. I’m in the south so more Flamenco than Gaitas over here!! I have interests in Asturias and plan on making the 1800km round trip in the Jag at some point. Still need to do a few shorter trips to get my confidence up…

 

LOL! More to Spain than Flamenco.


Probably had to look-up Hanno, Hamilcar, Hasdrubal, and Hannibal Barca of Carthage (and early "Ibaru" Spain) as well?
Celts are obvious, it's the Iberian side of the Celt-Iberian Peninsula as has gone lost in the mists of time.


Need a 'confidence builder', take the clawed-feline on a wide circle, include Extremadura, Costa Verde, then Eastbound to divert into Andorra, opposite side on the downstroke, by then up to dicing with some of the most competent, if rudely arrogant, mountain drivers outside of Appalachia, Yew-***-Eh. Or at least Pais Vasco?

By contrast, drivers in Galicia, Asturias and Cantabria tend to drive as if trained in Germany. Precise, polite, attentive, but passionless - much akin to their extensive EU-subsidized major motorways? Mayhap they worry the German financiers will take the concrete back if they drive like Italians?

Relax on the Southern return loop and back to home? Jaguar's were not meant to sit still, lest they get constipated, then s**t your entire bank balance ever so explosively! DAMHIKT!

 

Celts trumps Arabic based Flamenco for sure!!


I did a similar route in my Alfa 164. Most memorable road trips ever. And for sure, sitting is what kills these cars. Mine had been sitting for over a year before I bought it hence the issues that have popped up. It's my daily driver now and loving every minute spent!

 

FIAT Chroma (I had owned a 124 Sport Coupe in the USA), Ford Fiasco (same again), Alfa 75, Audi TT, longer-term leased Renault Laguna, our own RHD BMW 525, (I had owned a LHD 3.0 "Bavaria'), VW Touran, Lancia Musa, Mercedes folly, Ford Mondeo (Denmark only), couple of Citroen micro-Diesels... and a few even more forgettables, NOT among my iusual premium upgrades with Kemwell's US-prepay plan. Some better than others, tires the most critical. One adapts. Same as heavy trucks and varying loads require.

The problem with Gran Turismo is driving it alone, no relief driver of comparable skillset, so at least one of you can appreciate the scenery enroute better.

Solo, one daren't take attention off the road environment, so 'touristy stuff" cometh only at stops, morning, midday, and evening, scarce days-off, else out of a travelogue ... where photos or videos could be accumulated as taken under perfect conditions.

Jaguar .and one near-clone rented Thunderbird - needed for a West Virginia 2-lane blacktop run to a funeral, of all causes, as my 'usual' was a Buick Regal or Mustang 5.0 convertible - take some of the work out of a fast traverse.

Long as a Maine Coon cat, the XJ8-"L" is, but even on twisty 2-lane, it is just a great deal easier to make time without stress than lesser motorcars generate.

Even so, it's full attention to the road environment .... or one never makes it to 'golden years' intact.

At least in Mexico or South America, we'd hire a driver. Even so, Santiago to San Jose de Maipo was more stress than the Tet offensive, 1968.

Their highway legal system? Criminal Law. Not civil. So it wasn't remotely sane for a non-citizen to roll their own wheels.

Traverse a share of Buenos Aires 8,000 uncontrolled 4-way intersections, approaches blinkered all directions by buildings, as a taxi passenger? Grok in a New York Minute just how Juan Manuel Fangio's beginnings as a BA taxi driver honed such a superb F1 winner!

THIS... is where an Alvis Saladin would trump a Jaguar's advantages! Juan Peron may have only gone 'military' to survive local traffic whilst going for the typical Argie full-kilogram beefsteak luncheon?

But we at least got more enjoyment and better photos amongst the rations of sheer terror!