Y2K UK EXPLORER - Thumping/Jerking Under Pressure

Hi all - I'm hoping someone can help!!! I've been trawling the problems on this site to try to find out what's wrong with my 2000 Explorer but haven't had much luck which either means my problem is a terminal transmission or something simple I guess. I've got an intermittant problem with a jerking/thumping which seems to come from the transmission on hard accelerating and mostly uphill - it crossed my mind it could be a bad plug or 2 as it's due for a service having done 61k (last one at 50k!). The transmission engages perfectly and the engine idles fairly smoothly and this problem is present on about 10-15% of the time as it will sometimes accelerate fine but other times the thumping will be so bad you have to lay off the gas to stop it. The thumping speeds up with car speed. Should I sort the service out then see if it goes - Your help would be greatly appreciated - thanks

Paul
(England - UK)

From your description, it sounds to me like a misfire, or severe engine pinging (detonation before TDC).

I'm not sure what the PCM diagnostics are like in the UK. In the US, your 2000 would have OBD-II which incorporates a misfire monitor. If you have something similar on your UK-spec Explorer, get the computer scanned to see if there are any misfire counts.

With OBD-II diagnostics, there can be misfire counts without tripping the Check Engine Light.

-Rod