91 tercel engine knock

[ghutch]

Hello all,
i just purchased a 91 tercel w/auto tranny that has an engine knock. The knock is pretty noticable while in park and all but disappears when in gear. The knock returns though through acceleration. The knock is also weaker when the a/c compressor is on than when off. I'm not a mechanically inclined person so any help would be greatly appreciated. i don't know if its a vavle, lifter, rod, torgue converter, etc. Not sure what it will take or cost to fix it either.
Also none of the brake lights work. I checked the brake light switch, it works to disengage from park but still no lights?? If the brake light switch is bad, can it still allow it to shift from park and not allow the lights to work?? Or is there anything else I can check? All the fuses are okay.
Thanks Guys,

[Donald]

First thing you need to do is try and figure out what part of the engine the sound is comming from. Top, bottom, right side (towards the belte) or left side (towards the tranny). That will give us a better idea of what it might be.

A good way to help narrow it down is to use a mechanic's stethoscope and touch the probe end to different parts of the engine while it is running. If you don't have access to one of these (they aren't expensive by the way, about $10) try using a long screwdriver and put your ear against the handle end, while you touch the various parts of the engine with the business end.

For your brake light problem, did you pull the fuse all the way out and look at it. Sometimes fuses can blow and still look good, then you need to check them with a continuity tester (ohm meter) or a flashlight battery, a bulb and some wires.

[NickR]

A length of garden hose also makes a good stethascope.

I find it interesting that the knock gets quieter with the AC on. That sounds like good news to me. I can't think of any reason why an internal engine problem would give a different knock when the AC is on.

Listen carefully with the stethascope around the accessory belt area, near the AC compressor. If it sounds like it is coming from near there, I would remove the AC belt, run the car just for a very short time like that (does that belt also run the alternator, or the water pump?), and see if the knock disappears.