Ok, Jag folks... I need some help here on my personal car. 2004 XK8 with a 4.2. All was well, and one day the check engine light came on. I found codes p0171 and p0174 indicating both banks are lean. My car has 103,000 miles, and was in need of intake gaskets and seals anyway. So, I figured I would tackle that job in due time. In the meantime, I added some BG fuel sysltem cleaner as a geberal maintenace item, and replaced the fuel filter as I had no way of knowing how old it was. Not long after, my Restricted Performance warning came on. Finally got the time to do my intake, and all went fine. To my surprise, I had the same issues afterward! Let me get to the meat: Smoke tested the intake. Changed the intake gaskets and the seals between the upper and lower intakes. Smoked it again to confirm no air leaks all the way from the MAF back by sealing off the pcv and purge hoses etc. Fuel pressure is about 55. MAF is 4.00 to 200g/s dependent on load. STFT are as high as 25%. O2's are responsive, New fuel filter, new plugs and air filter about 3000 miles ago, replaced the MAF because I found a good buy on a new one. Even performed a hard reset to see if that would return the trims to 0. Still getting a p0171 and p0174 plus the Restricted warning almost immediately after clearing the codes, and then driving. Obviously, looking at the trims, we are indeed lean. So, I have seen many posts of this nature, and cant help but think in the end, we all will experience the same issue. But what do you guys feel is the main problem here? I see where guys have changed this and that with success, but it seems there is no 1 thing that seems to be an issue. (except the intake accordian, etc which I have ruled out). This seemed to come on almost "suddenly", and in the 3 years I have owned the car, it has run flawlessly. Give me your thoughts!

 

Well chopr, I had the same issue with my '03 at 105K miles. And did almost the same thing... replaced the intake gaskets. What I found when I did mine was ; the gasket between the intake elbow and the manifold was leaking. The way I fond it was while watching the live data for the fuel trims, I sprayed some brake cleaner under the manifold in that area and I the fuel trims plummeted. The key is watching the live data... you must have a scan tool with this feature. One other question, was the MAF sensor a new "JAGUAR" part? they can be very sensitive. Good luck.

 

Thanks, Bhpbug! I did replace the gasket under the throttle body, as well as the manifold end seals when I did the intake. Caution noted on my cheapo MAF sensor. I did see where my new MAF reads about 4.0 g/s at idle where my OEM one read about 4.5 g/s. They both read almost 200 at full chat. I have found that the STFT was pretty good at idle, but rapidly increases (almost immediately reaches 25!) when driving away under some load... pretty much ANY load. I just replaced my PCV thinking it probably couldn't hurt at avoer 100k miles. I did notice one improvement: My STFT was wandering around at idle, although not way out of spec. But, the reading wouldn't settle down. It is now very steady, and reads at or near "0" at idle. One other thing I noticed tonight: My MAP sensor is reading only 11 inches at idle. I would think 15 or more would be appropriate. Just to confirm the reading, I am going to attach a vacuum gauge for verification. I am sure the MAP reading cannot be right. I also noticed a slight misfire when first starting the engine. One more thing to investigate! I will report in as we progress...

 

What are the LTFTs at idle & if you rev to about 2500?

 

And what does the fuel pressure do as you drive and load changes? Does it stay near 55 all the time?

Don't suppose yours is one of the lucky few 4.2s that has a schrader valve on the fuel rail and can easily check the pressure with a gauge?

 

Same problem here. I will be replacing the air intake accordian since it is broken. I have a new MAF that I got at Napa installed.

 

I had the same basic problem w. my '99 4.0: check engine light w. restricted performance & running lean both banks. My indie Jag shop (factory-certified mechs) has seen it many times before & told me 95% of the time a new MAF sensor fixes it. They installed a new OEM sensor & problem solved, with no recurrence after 2k miles. +1 on bhpbug's caution re using a cheap MAF sensor - "penny-wise, pound-foolish" as our British friends might say.

 

When you performed the smoke test did you include the intake pipe from the throttle body to the air filter box?

 

Sorry for the delay in responding, but I now have the final solution. And you guys called it early on. I had replaced the MAF with an inexpensive part. Then I chased my tail, as you all read. I had an opportunity to "borrow" a good MAF and check the data on my scanner. You guessed it.... All good with a good MAF. I purchased a Delphi unit and scanned the car coming home tonight. Data normal. It's running purrfectly again! Lesson learned. And a BIG "Thank You" to all who got involved!

 

I have the same vehicle and problem as chopr (2004 XK8 w/4.2 engine). I was told to change intake manifold gasket & PVC valve. Unfortunately, the dealership sales the manifold & gasket together because its not recommended to just replace the gasket. Excessive price of $3000 for the manifold whole, PVC only $87. I never heard about MAF sensor, what's the cost on that? Should I dare go to a dealership for an diagnosis hoping for an honest answer? or stick with my mechanic who is honest but doesn't have the jaguar experience as dealer? My milage is 191000. Had the jag for 2.5 years now.

 

Since I seemed to parallel your situation should I try replacing the MAF sensor (OEM) 1st? or along with the manifold w/gasket replacement too?

 

Your regular mechanic should be able to perform a smoke test to identify air leaks, so don't start throwing money at the problem without more information.

If you do need a intake manifold gasket, companies like sng barrett, a site sponsor, can supply it.

 

Byrdlimo, If your car has substantial miles on it, I would expect the intake seals have begun leaking. Mine has 103k on it. The 4.0 and the 4.2 begin leaking after time. As stated, a smoke test will easily verify ALL leaks in the intake, if any, and then you can address them and not miss anything. Just FYI, if you decide to do the intake, it isn't particularly tough, just time consuming. Jaguar will tell you that the seals joining the upper and lower intake halves are not available, requiring replacement of the entire intake. Not true. Land Rover 4.4 V8 engine shows these separate, and they are available for about $80... roughly half what they sell for on Ebay. They are green; yours are gray. So, you will need: Upper intake seals (8), lower intake gaskets (2), front intake plate seal, rear intake plate seal, and throttle body gasket. You "could" replace the injector seals at this time, but mine were fine. Additionally, you may want to replace the two heater hoses that run under the intake, and also replace the small band clamps that you will find on the small coolant hoses with screw clamps. The hoses lose size under the band clamps over time, and tend to weep under pressure when they get old. Much easier to do now. Also, the plastic coolant distribution log at the front of the engine may need attention. Look for signs of coolant leakage, and replace this unit (if needed) when you have the intake off... much easier to get to the rear bolts! Be careful with the yellow clip. The new one doesn't come with it. About $110. There is also the plastic NORMA fitting (black plastic, in the heater hose and has a tee that goes to the throttle body) at the left rear of the throttle body that should be looked at for coolant leakage. If you want to change it, just twist it until the retaining ears are up on the little ramps, and then pull it apart. There is an o-ring seal at that joint. You may break the security clips on the fuel injectors, as they get very brittle. If you wish, the set of injector clips is available (on Ebay, if nowhere else), but you will have to cut the wires and solder the new pigtails in place. That's about it for my two cents! Good luck!

 

Wow, Thank you Chopr. I really appreciate your detailed answer. unlike many of you guys I'm not mechanically wired but depended on shop mechanics, so I appreciate you informing me so I have a clue on the subject and not stabbing in the dark. I will let you know the results!

 

Great write up! You make it seem so easy... How long does it take to tackle all these gaskets/hoses/clamps?