Gus, I believe the thud is the shifting of the transmission into limp home gear. After reading an additional thread I think the problem could be a dirty throttle body. Other owners seem to have had the same problem and the codes they get are P0328 or P0333. I will attempt that project next. I did swap the knock sensors from one side to the other but if my intuitions are correct that won't remedy the problem. Do you agree that could be the problem? Thanks for your input. Paul

 

I agree that when it goes into restricted performance mode, hard jerks and noise do happen, especially while under acceleration. Mine would do it so bad the rear tires would chirp as the engine slowed down. Cheap knock sensor fixed my problems.

 

Paul,
I agree moving the sensor is not a fix. A knock sensor is designed to identify pinging in the engine notify the on board computer to make the necessary adjustments with air, fuel and spark. P0328 is a high voltage bank “A” and P0333 is a high voltage bank “B” so both are seeing the problem unless you did not get and clear the first code and you are now reading both after you swapped the sensors. Once they are activated the car will go into limp home limiting the engine speed to 3000rpm. See this video http://www.youtube.com/watch?v=0xI94ZDF54Y I had a situation with my knock sensor http://www.gusglikas.com/AutoRepairR...erformance.htm We found a bad sensor and a problem with the wiring after replacing my TB, you need to check it. The sensors are cheap and in most cases easy to replace. What concerns me is the “Thud” do you have any other codes to identify what is causing it?

 

Gus, the first time it happened I beleive it was when the car stalled it shifted into limp home gear. thus the thump. The next two times it was more of a click then a thump. Now when I hear the click I pull to the side of the road because I know I am in a stall even beforeI I feel it. I think your advise of cleaning the TB is good next step. No additional codes other then the ones mentioned. Since the knock sensors are swapped if it happens again and the code indicates the other bank then it is a knock sensor.
There is one other thing I should mention, I had an exaust leak in the front resonator (where the exaust pipes emerge into the single muffler before seperating into the tail pipe with mufflers) since a replacement could not be found there were two straight pipes, one for each side welded in. I only mention this because of the sensitivity of these XJ8's. Could exhaust have anything to do with emmision? Paul

 

Post cats', doubtful.