I have a 94 z28 with LT1, i am hearing a knocking sound coming from engine, only does it every so often or when its cold. Sounds like something loose inside maybe or something on block loose, like a a lil drummer boy in my car lol. To me it sounds like its rolling or turning, car drives fine no smoke or anyting else. any ideas or suggetstions please help, Thankz

 

A common (no problem) sound with the LT1 is piston slap on cold start... sort of a knocking noise, that disappears as the engine warms up. Wouldn't describe it as "rolling" or "turning" though.

 

does the car still have ac? I have a 94 and the ac pump makes a knocking noise at an idle but stops when you give it gas, and sometimes makes no noise at all

 

You can tell if its piston slap by doing a little test, granted this isnt good on the motor but its a test. Right when you start the car up when its cold and you here the knock, if you give it a couple revs to like 2.5k or hold it at like 2k for a few seconds the pistons will have swelled enough pretty quick to the point where the sound is gone. If its a knock it should be persistent.

 

I tried the test you said. When I did that I couldnt hear anything at 2500. It only does it when its at lower rpm, like under 1000. when im driving it or acclerating you really cant hear it. I also tried this..... turning the engine over but not starting it, thats when u can hear it the best, or at idle with car in park or drive. this one has my scratchin my head. Also the a/c compressor is gone, I did the a/c delete pulley. thanks again guys for helpin!

 

OK, I narrowed it down, I put the car on the ramps today with the engine running. It seems to be coming from in the oil pan near the back on the engine where the tranny meets. IT only makes the noise when you are below 1000 rpm' or at idle. when driving it runs like a champ. Exhaust, starter and everything is tight . im still have no clue, lol
thanks again guys

 

sounds like a rear main bearing, I have a mustang do the same thing.

 

Is that hard or expensive to change out? I am asking beacause this guy i know has an engiine out of a 97 and wants 300 bucks for it. so would be wasting my time trying to fix it, or should I just buy the other engine??

 

check the flywheel/ flexplate bolts. you dont say auto or stick but if its an auto i would bet on torque converter bolts. you may also want to inspect the flywheel/ flexplate for cracks.

 

Its an automatic, 4l60e. I just had the tranny rebuilt and the the tech said he inspected the flywheel and it was ok, brand new converter and shift kit but ill make sure to check those bolts. Is there any possibilty that a bolt on something is loose inside? thanks for the continued support

 

If you just had tranny work done, I would start looking there, first. Check the torque converter bolts.

 

OK, I checked the torque converter bolts and they are good and tight. Last night I drove the car to work. It snowed last night and when I started it to come home It was extremely loud for a few minutes then calmed down a lil. Still scratchin my head, lol

 

OK i called guys at tranny shop they gonna take it back in and look at it closer, maybe broken flywheel or loose TC bolts that i think are tight but might be backing out....... thank guys

 

Check your right side motor mount (The rubber inside wears & allows the metal center to strike the mount)~ mine was rapping so bad I thought I'd lost a wrist pin.

 

Thaks alot, ill be sure to check that motor mount? what kind of noise does a cracked fly wheel make? lol