Howdy from Texas and our sizzling 100+ degree weather! My 1999 XJ8 with 98K miles had been running smoothly with no problems. This morning, it is missing horribly at idle, is on "Restricted Performance", and it is showing P0300, P1316, and P1647. Codes 0300 and 1316 refer to engine misfires. I recall a couple of years ago I got a code that indicated which cylinder was misfiring. I checked and replaced the ignition coil and it had been running well ever since. However, the current codes do not indicate which cylinder is misfiring (code P0300 refers to "multi-cylinder misfires"). I read a number of threads on P1647 concerning Heated Oxygen sensors; however, they were all referring to six cylinder engines. They all stressed that the correct sensor be replaced with a Jaguar replacement, Bosch, or Denso. Any suggestions on correcting the Restricted Performance and cylinder misfires on my XJ8 will be greatly appreciated.

 

The first thing we need to know is if the secondary chain tensioners have been replaced. If not, one may have jumped a tooth resulting in the misfire.

 

RJ237, thanks again for your suggestion about the chain tensioners. I've had the car 3 years and I have not replaced them, and I doubt the previous owner did so. It had 78K miles when I purchased it. While I have limited experience with Jags, I would think that if the chain had jumped a tooth, the timing would be off and it would run poorly consistently. I just drove the car and despite the missing at idle and low RPMs, it accelerates fairly well, almost normally with no missing on gradual acceleration or steady speed. However, if I floor it while going around 40 MPH, it misses a bunch and seems reminiscent of fuel starvation. Some of the threads I read suggested a filthy fuel filter as a possible culprit. I have located a fuel filter but now I simply need to know where it is located on my XJ8. This seems to be a cheap, easy solution if that's actually the cause of the misfires. A box appeared on the Forum screen for asking questions, so I inquired about the location. I did not know it would appear as another thread....geez. Anyway, if you can point me in the direction of the filter, I would be most appreciative, again.

Rolando

 

The P0300 could be the cause of the other 2 codes you are getting. I would recommend a methodical inspection of the components that would create a random misfire condition. The lack of acceleration is a result of the ECU trying to prevent engine damage due to the misfires.
First start at the intake snorkel tube, remove it turn it over and make sure you have no cracks in the corrugated section. Next remove and clean the MAF sensor and the connection. Make sure the plug is clean and solid not heat cracked and loose. Then go to the throttle body electrical connectors and check that each one is clean tight and not heat damaged. Lastly inspect the part load breather tube coming out of the left side cam cover and be sure that there are no cracks or breaks in the tube.
If you scanner is capable of reading them it would be of great help to know the STFT (short term fuel trims) and LTFT (long term fuel trims) you should also be able to read the fuel pressure while running. You need at least 45 psi to 55 psi.
Check it all out and get back to us.

 

Thank you Vern. I will inspect the items you mentioned. Lastly, I do think my scanner is capable of reading the STFT and LTFT, and hopefully, the fuel pressure while running. If it is capable, I will come back with those readings and any weird findings that may come up.

Rolando

 

Reread the recommendation to check the tensioners. Most critical. Fuel filter is above and forward of the left half shaft.

But I think your timing is off.

 

Jhartz has a valid point but when trouble shooting I like to always eliminate the easy verifiable points before tearing the engine apart. One thing you must plan on is to pull the cam covers and verify the condition of your tensioners at some point.

 

Thank you Vern, RJ237, and JHartz for your helpful suggestions. Vern, I checked the items you mentioned. The snorkel tube was fine as were the electrical connections to the throttle body. No heat damage or cracks. I I wasn't able to locate the breather tube coming out of the left cam cover, but I did have a 2" slit in the corrugated tube going from the MAF/air cleaner to the throttle body. The fuel filter was after-market and was filthy with cloudy gas dripping out. I plugged up the slit as a temporary fix and went for a drive. Still missing at idle, she accelerates well but misses a bunch when I floor it when I'm dong a steady 40 MPH. The amber light and "Restricted Performance" initially disappeared, but they returned and disappeared a couple more times. It still idles really crappy and barely moves unless I give it lots of gas. I could not get the STFT, LTFT, nor the fuel pressure with my scanner.
RJ237 and JHartz, I thank you for your advice and I will see about checking the tensioners (albeit when the weather is a bit more bearable). I will post my findings at that time.

Rolando

 

If that slit lets in air then you have a serious problem as the whole intake past the MAF must be vacuum tight.

Even so, inspect those tensioners etc as your engine is on borrowed time otherwise.