Hello, I just joined this forum a couple days ago after I bought my 94 Firebird Formula. It has the LT1 V8 in it and 129K miles. When the car starts up, the engine knocks for about 2 minutes and after it warms up, the knock goes away completely. The knock sounds like it is coming from the driver side valve cover. After the car is turned off, and started right back up warm, the knocking will be there again but will go away after another minute or two. I changed the oil and am going to change the spark plugs. Can anyone think of anything else??? Thanks!

edit: Also, the car is running a little rough, almost like on 6 or 7 cylinders. (very similar to how my third gen camaro ran when it had clogged injectors)

 

Maybe the knock is an exhaust manifold leak, at the header? This sounds like a knock if it's really bad and causes a lack of power. Try to pin point exactly where the noise is coming from, that will help.
I'm no expert though. Good Luck

 

Knock or tick? A deep sounding knock is likely a rod bearing. A tick could be a rocker arm, exhaust leak or lifter.

 

Beat me to it.

 

It sounds more like a tick, especially since it sounds like its coming from only the drivers side. I think the guy probably ran 87 octane in it. Could this cause this? Also, the spark plugs have not been replaced yet. Could this also be the cause?

Also, I took the valve cover off but did not pull any of the valve train. I look at everything, expecting to see something blatantly obvious making the noise. This was not the case. All the rocker arm bolts seemed like they had the same amount of threads behind them on the stud so I figured they were all tightened evenly. Does this make sense to anyone? I've never done valve train work before, so this is new to me.

 

Yes, I would definitely do plugs if they are stock. As far as the rockers needing adjustment, maybe they do, but I would get the plugs and wires(if needed) taken care of first and then go from there. Suggest going with NGK iradiums, gapped at .050 (make sure the gaps are correct using a plug gapper (not a flat bladed rocker spacer type).

BTW: Just because the rockers are evenly tight doesn't mean the adjustments are correct---but as mentioned, don't worry about the adjustment at this point. Just make sure that you are getting spark to all 8 cyls.JMHO

 

Thanks everyone for the responses! I took my car over to my friends house to have his dad check it out quick (his dad is the head mechanic up at the local ford dealership). He said without a doubt he knows its an exhaust manifold leak.

I thought this was SWEET!!!! I only paid $1200 for the car and it's in MINT shape, it just has a few miles on it. So yea, I've done the exhaust manifold gaskets in my 3rd gen camaro (305ci) so I can't imagine this will be too much harder. Thanks for the replies again! Hopefully this takes care of it!

 

Just make sure that the cat isn't clogged, when this happens it can often blow gaskets, exhaust has to go somewhere.