I have an 04 XK8 convertible with 109k miles that I've had for a couple of years and it's the honest truth that I have yet to go more than about 200 miles without a CEL for one thing or another. I've replaced the injectors, coils and harness plugs, fixed numerous vacuum leaks, smoke tested it till my eyes bleed, replaced the fuel filter, replaced the MAF sensor, changed spark plugs, replaced VVT seals, and lord knows what I'm forgetting but this is getting old. Real old! If the thing wasn't so much fun to drive and wasn't so damn pretty, I'd have launched it a long time ago. Last fall I was driving it and the light came on again and the reader gave me misfire codes for numbers 1 and 5 and now it added codes for too lean banks 1 and 2 and excess emissions which I expect are because of the misfires I can't even feel except at cold startup. I got so honked I parked it and now I'm going to try again. So, in an attempt to get some kind of foundation for better overall driving and considering the fact that this car was apparently poorly maintained by the prior owner, I'm planning the following:

I'm going to tear the intake off and replace all 4 oxygen sensors, replace the intake gaskets, closely examining all components for cracks etc of course. Then comes replacing the valve cover gaskets and plug well seals as I think at least one of those is leaking. Replace the one leaky VVT seal that I just replaced last summer. Possibly replace the coolant temp sensor just because. Do a leakdown test of the injectors. Then try it and see what happens. If it says misfires again I'll start moving coils and injectors around to see what that tells me.
I am aware that the quality of the rebuilt injectors and O'reilly Auto Parts coils is in question. I don't intend to take any chances with the oxygen sensors. However, it seems logical that they are past their prime and can negatively affect so many things and while the intake is off accessibility is maximized.
So, am I losing my mind or what? I welcome the thoughts of experienced Jagsters.

 

have you checked the air intake tube for cracks in the accordion portion - especially on the underside that is subjected to the heat of the engine? Made sure it is seated properly on the throttle body and at the intake box/MAF sensor? What about the part load breather tube (also plastic accordion type material subject to cracking)?

 

Hi Steve and thanks for the reply. One of the first things I did was change the MAF and check the intake tube with a fine tooth comb. I removed it, flexed it and looked at every square inch. All clamping areas were checked and nothing looked substandard there. I did find problems with the throttle body snap in connector and replaced that as well as the dipstick seal. Smoke testing indicated no vacuum leaks after that. I'm not sure what the part load breather tube is? I replaced the o-rings on all the tubes from the valve covers to misc points and examined the tubes at the same time.

 

Make sure you avail yourself of a basic ELM327 code reader with a corresponding mobile app. I would let you read the fuel trims that are key to this long-winded maintenance quest you are on. In short, trims are how much additional fuel the ECM has to add based on the feedback of the upstream wideband O2 sensors. Normally, it should be near 0. Anything under, say, 5% is great. Above it means there is still some unmetered air getting in (leaks) or you have a failed/incorrect AFM. Remember that trims are a function of load and rpm, it is not a single number. Best is to start testing at idle (high vacuum).

Of course, if you plug a major leak, you might want to do the more complete "hard" reset at the battery and check that the trims are back to zero.

There are a couple of less obvious areas for air leaks. You did a smoke test, so maybe you are ok.

• There is a gasket/o-ring for the AFM that is sometimes missing/damaged.
• The EGR tube sometimes develops leaks in the accordion section (between the passenger-side exhaust header and the throttle body)
• VVT seals already mentioned (if you see oil, air is likely going in as well)
• (lower?) Intake manifold seals (there is a Range Rover part for these)
• The weird brake booster vacuum line bushing on the throttle body (there is an S-Type part for these)
• All exhaust gaskets

Other maintenance to keep an eye on is the condition of the (4) rubber lines to/from the oil cooler. They are "hydraulic" parts and are largely understood to have a life expectancy of 10 years. When they fail, the rubber separates from the Al and the engine oil is dumped on the road in seconds (better turn that engine off FAST). There is obviously no oil pressure left and you need a tow home.

Best of luck, keep us posted.

 

Fmertz, thanks for your in-depth information. It helps to have someone obviously knowledgeable and familiar with the XK8 to help guide me into the diagnostics realm as opposed tp parts changing. The parts changing I'm planning is basically the result of the age of the car. I really want to start from the block up just so I know what is there after seeing some debris around the intake that looks like someone may have been there before. In response to your suggestions: I don't know what the "AFM" is. Can you please explain?

I have already replaced the ridiculous connector on the throttle body with new OE Jag and smoke test shows nothing there anymore. However, the EGR tube I'm not sure about. I'll double check that. I haven't heard any exhaust noise so the exhaust gaskets were the last thing on my mind but I'll look for sure.

Now, the fuel trims are another story. I have read references to them on this forum but to be honest, I don't have a clue as to how to read them. I have an Innova 6100P reader which seems to have some capability. I'll have to connect it and run thru the menu to see if there is anything that says "trim" or something similar. Would there be another label or name for this area? I hate to sound like an idiot as I have worked on everything from hotrods to city buses and street sweepers for over 40 years but the involved use of electronic scan tools is not something I have lots of experience with. I can bumble my way thru usually but it may take a couple of tries. BTW, when I moved the Jag across the yard to my shop the RP message came on. So the current issue is apparently significant.

And your note about the oil cooler hose sounds like a good idea. Considering the amount of issues I've had with this car, I'm surprised that failure hasn't already happened to me!

Update: I just checked my reader and the stored data does show STFT B1 24.2% . So the reader is probably capable of reading all of the trim info. I'll tackle that tomorrow. I'll find and get fresh data and go from there but if I get the same kind of data I'll attack that problem specifically.

 

AFM is the air flow meter, by the airbox.

You probably need to read up on fuel trims, they are a standard OBDII feature. The numbers you will be looking for are the long term fuel trims (LTFT) and short term trims (STFT). There is one set per "bank", basically one per exhaust manifold. From memory, bank 1 is the driver side in the UK. These numbers are organized in a matrix, like the elevation on a map, indexed by engine load and rpm. The STFTs are basically the more immediate reading off of the O2 sensor (they change quickly). The LTFTs are the average of the STFTs over 2 minutes, for that rpm and load.

In a "perfect" engine, all the LTFT are zero: the engine runs perfectly clean with the base fuel table. In the real world, there is always some form of air leaks, or imperfect read from the AFM and LTFT are a few %. OBDII codes (171, 174) are thrown when these trims go over 25%.

Easiest is to start at idle (fixed load and rpm and high vacuum) and have a look at these trims. Anything over 5% probably deserves some attention.

Best of luck, keep us posted.

 

OK sports fans, today has been a learning experience. Now I need to learn more. Here is what I did:
1. recorded all active codes. They were PO 301, 305, 171 and 174 and 1316.
2. Connected the reader and looked at stored data: Calc load 16.5%, ECT82, STFT B1 24.2%, LTFT B1 3.9%, STFT B2 25.0%, LTFT B2 .08%
3. Started the engine, read live data cold eng: IAT 72 degrees, RPM 645, Calc load 16%, ECT99 degrees, Spark adv 7 degrees. STFT B1 6.3%, LTFT B1 19.5%, STFT B2 4.2 VARYING TO 6.3%, LTFT B2 19.5%, 55 PSI fuel pressure, MAP 10 in/HG, MAF .63 lb/min.

4. Let the engine reach operating temp and the ones I watched closely were: STFT B1 -3.1%, LTFT B1 16.4%, STFT B2 -7.8%, LTFT B2 15.6%
5. Cleared all codes noting that while I was reading them it added a misfire code for 306. Drove the car about 5 miles at varying speeds expecting a return of the CEL but nothing. Dangit!
6. Let the car sit outside for over an hour expecting it to get cold but it was still just above the blue range on the temp gauge. Drove it same route again and nothing.

7. Decided that the FT readings were obviously out of whack regardless of the lack of CEL thus far. Figured that was incentive to try the method of spraying carb cleaner around any points of possible leaks so I did. Sprayed everything I could think of except the exhaust and no reaction at all.

Now I'm no expert of course but the only conclusion I can glean from this is that my initial approach wasn't far off the mark. I suspect aging/failing oxygen sensors are sending false data to the ECM. The misfire issues perplex me considering that the car runs smooth as silk except a little roughness on cold start for a minute or two. I intend to pull the coils tomorrow and look for oil in the tubes. However, it seems to me that the thing to do is what I set out to do in the first place. Remove the intake and rocker covers, replace the 4 oxy sensors with new Denso units, Reseal the intake and upper plenum, reseal the rocker covers and spark plug tubes, all of this while thoroughly examining every tube, oring, gasket and connection of course, clean the EGR valve and replace the gasket and then try it again.
Oh, one other possible approach: Because I have repaired numerous leaks on this car especially last summer but no "hard reset" was ever done, I could try doing the reset before I do anything else and see if the fuel trims look more normal...?

Your sage thoughts would be appreciated!

 

I should probbaly have a look at mine but I fear the results. I know my car is retarding gintiion somewhat because my intake temp is far too high as my intercooler pump isn't working. If you have a cold engine that never warms up I would replace the thermostat, it's most likely stuck open.

 

For now ignore cold trims.

With hot engine, parked, do the trims drop when you rev (say 2500)? If so you have an air/vacuum leak. If not, you're looking for something else and as the trims are similar per bank you'd be looking for an item common to both banks (such as MAF).

 

Thanks Jagv8, I'll try that test next session first and see what happens.

 

Well I decided to tear off the top of my 4.2 to seal, clean and bring everything up to snuff. Got it all off at last and started to change all 4 o2 sensors and hit a brick wall. I've been trying for 2 days on and off to figure out how to get to the sensor connectors. The bracket on top of the bell appeared to have 2 bolts so I got ot those 2 and now it feels like there is another one I can't see. My sensor cables for the upstream units go behind that and I can't get my fat hands back there. Suggestions please!! UPDATE: Sometimes I can't see the forest for the trees. After this latest post I tried another variation of the search and found a post that pointed me in the right direction. I might add that removing the front 2 bolts in the wiring bracket added welcome room to get my chubby fingers in there.

 

Well done. My giant hands often keep me from being able to complete various jobs that "normal" guys can do. Fortunately I have a small-handed neighbor who is usually willing to help. We installed my newly-refurbished starter in my trusty 1999 Ram this past Monday afternoon. I could not get my hand (or the socket wrench) anywhere close to the top mounting bolt tucked way up above and behind the starter. He came over and installed that bolt for me with room to spare....

 

With everything off, be sure to double check the seals between the plastic intake and the short aluminum runners attached to it. There is another set of seals between those parts, separate from the more conventional intake manifold seals. From memory, Jaguar does not offer these seals by themselves, but it has been reported that there is an equivalent Range Rover part that fits. To be clear, these seals are not known to fail all that much, but it is worth checking while you are there. They are sort of expensive too, IIRC.

While there, also replace the 2 dreaded heater hoses running down from the thermostat to the octopus hose. Double check the vacuum line to the fuel pressure sensor.

 

Fmertz, I've been trying for days to identify the part numbers for those upper seals for my 2004. I didn't want to take the intake apart til I was sure I had parts so pictures don't help me. I may have to resort to the phone.

 

I hope this might help. I found a post from brgjag that mentions these seals

https://www.jaguarforums.com/forum/x...3/#post1272301

He notes 8 separate seals, which are shown on this LandRover page (in the Heritage site, go figure...)

https://parts.jaguarlandroverclassic...nd/land-rover/

 

Thanks michaelh. I had seen that once before and it still left me confused because I don't have a LR vin # to relate to. I'd like to change these seals but I really hate to throw another 125 bucks at this car if I don't have to. It's a catch 22, can't see them without taking it apart. If I take it apart I'm stuck no matter the price. Unless I just reseal with black RTV...reluctantly. On the bright side of this project: I have now changed all 4 oxygen sensors and did so without removing the cats or digging through the carpet to try to use the access holes. It took a soaking with PB Blaster and a 30 inch long 1/2" socket extension with a swivel joint and a long handled ratchet to break the lowers loose but when the popped, they were easily removed by hand. The uppers were a little bit of a pain but with the rocker covers and intake off it wasn't that problematic.
I was never able to get the engine to respond to dousing carb cleaner around the base of the intake when trying to find a leak but when I removed the intake both sides of the thin metal gaskets were coated with oil. It didn't sit there long after removing the bolts, some of which were significantly tighter than others, before I picked it up off the engine. Therefore, I don't see how the oil could have gotten so spread out in such a short time. This leads me to believe that there may have been a leak there.
I did also find the sides of the coils were all smeared with oil and four of the wells had some oil standing around the bottom of the spark plugs. I don't know how much oil it takes to cause a misfire but this wasn't good nonetheless. I'm trying to heed everyone's advice here on all the things to check and have spent quite a bit on hoses and such as a result. But I have a bit of confidence that I'm making some improvement.
I think after getting this thing back together, I'm going to do a "hard reset" because of all the things that have been done and the fact that I have had the battery neg cable unhooked for two weeks anyway. Seems like the thing to do to start with a fresh slate. The PO 1000 code has never left the scanner since I've owned the car so maybe I can get past that for once?!

 

LR part # 4526549. See this other post from brgjag:
https://www.jaguarforums.com/forum/x...8/#post1148204

The oil around the plugs will be tired spark plug boss seals AJ86874 (8 required).

edit: brgjag has documented the procedure:
https://www.jaguarforums.com/forum/x...5/#post1071233

 

subscribed

 

In case that the plenum changed for 2004 on, perhaps double-check as the two options are somewhat different, I'd hate to send you in the wrong direction:


4526549



LR00678

 

Thanks Michaelh. I finally decided today that the only way to be sure was to take it apart. I'm glad I did. Upon closer inspection I noticed oily vapor staining in a couple of areas on the aluminum that indicate a possible leak. When I took the screws out and immediately lifted the runners off the plenum, there were two areas that were coated in oil and look like leaks to me. I was able to match the seals to the pics you provided and ordered a whole set from Parts Geek for 35 bucks including shipping. I forgot to put a pic on my laptop to attach but I'll post one in a few minutes.