I bought a 1999 Jaguar XJ8 with 75000 miles on it a two months ago. The seller gave me all the receipts, and I found that before he sold the Jaguar to me, the Ford Dealership deleted the P0171 code and rerun test.

I did not have any problems with the car until 3 weeks ago when "restricted performance" showed up and now the CEL is on. Since that I can't go over 300 rpm.

I read a lot about "restricted performance" and it is usually a vacuum leak. I checked the air filter, full-load brether tube, air duct, and cleaned MAFS, but no improvement.

I am thinking to take it to the shop for a smoke test. I will appreciate any advice on what to try. What about the knock sensor or fuel filter, because I have also one pending code "Fuel Air Metering".

 

I had this problem and it was the part load breather hose. It had apparently broke near the end where you pop it off to clean. Electrical tape made a temporary fix. It sounds like you still have a vacuum leak.

 

Vacuum leaks usually show up as lean on both sides. Strange that you are getting only one. Is there any documentation on a thermostat tower replacement Often, on the XK8 at least, a tech will lift the intake manifold to get to the rear bolts. That could lead to a leak on only one bank.

Here is the 'grocery list' from JTIS.

 

The thermostat has been changed at 60 000 miles.

 

I had a bank 1 only, and cleaned the MAFs to correct the problem. I agree with testpoint, it sounds more like a connector or sensor issue than a hole somewhere. Could the valve cover gasket on bank one be the cause? Do you have any signs of oil leak on that bank? Did you 'reset' the computer after doing any MAFs cleaning?

 

I don't see any oil leaking on bank1. I did not "reset" the computer after cleaning. Do you mean to disconnect the battery terminals? Is it "reset" to connect the ground cable for a second to the positive cable?

If I will reset the computer, what is the next step? Run the car for one hour? I am assuming that all sensors need time to "reset."

 

This is not an uncommon code for these cars and we see it a lot on this forum. I am attaching the OBD codes to help with you troubleshooting if you elect to take it on. http://www.gusglikas.com/images/Auto...J27%201999.pdf I am also sending a troubleshooting procedure that seemed to work for others http://www.gusglikas.com/images/Auto...otos/P0171.pdf
You may want to look into your intake and vacuum system for leaks. The on major leak I found on mine was in the bellows between the MAFS and the TB. http://www.gusglikas.com/AutoRepairA...HoseRepair.htm Good luck and let us know what you find.

 

I removed air intake and looked for a hole or any damage, but everything looks good. Based on ODB troubleshooting it may be a fuel filter. I am thinking to call dealer on Monday and order a new fuel filter.

 

The 1999 filter style is very common, and you can do it quite easily yourself with a couple open spanner wrenches, if your up to it. The autoparts store has your filter for less than $15. The newer style filters are much more difficult to R&R and I could only find it from the jag dealer.

 

I just had the P0171 show up today on my daughter's X-Type. She said that the car stuttered a little bit, then "Cruise Control Not Available" showed up on her display, even though she wasn't using it. I cleaned the Mass Airflow Sensor with MAFS cleaner, and so far, so good! I'll show her where the fuel filter is tomorrow and let her get a little dirty turning wrenches on it, for grins and giggles

 

I tried to replaced the fuel filter, but I am not able to do it in my garage due to bad access. I will take the Jag to the shop to replace the fuel filter. I will post if I get any results on "restricted performance"

 

It sounds like you are plugging away at it.

 

The day before I replaced the filter I took the jag on a road test(to determine if there were any differences when I changed the filter) and I was able to go over 3000rpm and on the sports mode the jag was OK.
The filter has been replaced today and the car still does have a poor performance between 40 - 60mph on regular mode. The mechanic told me to add Techron to the gas. I used injector cleaner from Lucas approximately 3 tanks before. On Saturday I will make a 200 miles trip, so thinking to add Techron to the gas.

What can I try now? RESTART? The check engine light is still on.

 

If you fixed the problem the CEL will go out after you have met the 'drive cycles' requirement but I would clear the code and see what happens. Got a code reader? Most of the 'free' auto parts places will no longer reset the CEL for environmental reasons. The shop that replaced the filter should reset it.

 

Good News. On Saturday I made a 200 miles trip. I read on the forum that some members had a problem with Shell gas. I was using all the time V-Power. So, I was thinking to stop on a different gas station. I filled up the gas at Conoco-Phillips and added Techron (Fuel system cleaner for 20 gallons). After 120 miles the CEL was still light on. Then I drove about 10 miles and stopped to shop. I started the engine and the CEL was OFF. I was really happy that the check engine light is off. Since that I drove the car a few times and no problem.

Here is a summary of what I did to solve the problem. It is for a future reference.

1. Checked air intake for hole
2. Checked Air Filter.
3. Checked full-load brether tube
4. Cleaned MAFS
5. Replaced FUEL FILTER
6. Added Techron (Fuel system cleaner for 20 gallons )

The mechanic also told me that the quality of gas in the Midwest is sometimes bad and he changes the fuel filter on his personal car every year.

I have a question for the members. I wanted to change the oil, but I checked the history and the Jaguar dealer used Castrol 5w30, but not synthetic oil
(this is my guess based on the price that they charged.) I was thinking to put Mobile 1 full synthetic oil. What kind of oil do you use? Should I use just Castrol GTX?

 

This is exactly what I did first. I cleaned the MAFS with the proper spray cleaner and had the Check Engine Light reset. It's been 100 miles so far and no more surging, or CEL.


Good to hear about your car lining back out, properly! I love the hell out of conventional Castrol GTX. It's my conventional motor oil of choice. run it for 3,000 or so miles and check your mileage. On the next scheduled oil change, try some synthetic of your choice and see if it affects the mileage or not. On my main driver, I've found little to no advantage in fuel mileage, by switching from conventional to synthetic. Your mileage may vary, of course.

 

Both are good oils and have qualities but at times a change to a synthetic can develop leaks around the gaskets that may take care of themselves. Aside from giving you my opinion you can read about oils good and bad and the why at this link http://www.bobistheoilguy.com/cms/index.php I hope this helps. It is good to know that your car has recovered.

 

Just had my 2004 XJ8 checked out for the same kinds of codes and found 2 sources of air leaks downstream of the MAS. The first one was a minor vacuum leak at the vacuum line connection at the front left of the engine, visible from the topm. The second source, considered the main vacuum leak, was the connection of the air box bellows connection to the throttle body. A faulty hose clamp failed to apply enough force to prevent leakage. After both leaks were addresses all was well in Jag land and my smog test concluded without a hitch.

For what it's worth, I have used full synthetic in all my vehicles including my Landcruiser which stayed clean as a whistle for 365K miles when I sold it.
My Dodge cummins diesel is topped off with Amsoil and after 195K miles the turbo on it is as tight as it was when it was new.
It is my general understanding that the use of a top synthetic oil gives your engine over 6 times the oil film strength and significantly reduced carbon in the oil which is a main contributor of wear in engine parts.
How it effects my mileage would be a minor concern since that is more likely to be associated with the oil grade and subsequent viscosity.

Just my humble opinion and

 

thanks

 

In the past, warnings were given about switching to synthetic oil because it could harm the engine. The reason for this was
that many synthetic oils contained esters, which are organic compounds mixed with alcohol. This combination was often
hard on seals in the engine, and would cause them to wear down and start to leak as the synthetic oil would remove the
sludge and gunk, built up over time, that was actually helping to seal.

Synthetic oil technology has improved over the years, and most cars on the road today should be able to use either synthetic
or regular oil, so long as the proper weight is used. In fact, some new cars require synthetic oil. However, one exception is with
older vehicles built prior to 1990, especially those with high mileage. The seals in those engines may not be able to handle the
additives in synthetic oil. However, that doesn't mean it's impossible to switch to synthetic in an older car.