A few problems

2001 xterra; v6; 155k miles

After I changed my oil, I noticed a clicking sound coming from the top half of the engine. I could only hear it with the hood up. Thinking it might be ignition related, felt each plug wire, but couldn't feel anything. Any suggestions?

Another problem (possibly related/contributing) - stumbling in 1st and 2nd gear, only after engine is good and warmed up. Doesn't happen at all with cold engine. Could this be a fuel filter issue, when engine is cold doesn't happen because of the xtra fuel being pumped? Was thinking it could be my clutch starting to go - but that wouldn't explain why it only happens with a warmed engine. Any ideas? When I changed the oil, I added some lucas upper cyl lube/injector cleaner and the problem almost went away, but not quite.

You don't provide a whole lot of amplifying information (history, type of oil, how long you have had the truck), but very often that clicking sound comes from valves or valve lifters. If, for instance, the engine has not been cared for well and you put in a synthetic, it could have cleaned the shit out of the valve train, unmasking a problem with the valves. My advice is to change it aggressively for a while and see if it clears itself up.

Bruce S.

Try adding Lucas HD Oil Stabilizer. Makes a big differance in mine. Mine "ticked" when I bought it, so on the first oil change I subsituted a quart of Lucas HD Oil Stabilizer...no more "tick".

You're on the right track with the stumble. Keep adding the injector cleaner.

Jeff!