Ok so my 1991 camaro rs 5.0 tbi 46,000 has been making this knock sound and it sounds like it comes from right under neath the valves. I'm worried because now i'm nervous to give it some gas and let the rpms go up....is it the valves or the piston? The sound goes away when i drive but then when i get off a highway that i been on for more then 5 miles i can hear it again. Will the stp combustion stuff will help could it be spark knock PLEASE HELP!!
Thanks

 

Give it a oil change with some 5w-30 and use some of that thick lucas additive that would cover up the noise if it is a lower end or rod knock and will give you more time till it comes apart

It could be that the rockers need to be adjusted but if its ''under neath the valves'' like you say its most likely a lower end knock

How many miles are on the engine?
When was the oil changed last?

 

the oil was changed about 1 year ago but i havn't put alot of miles on it and im constanly adding oil (had a small leak fixed it) it all together has 46,567 miles on it and is the knock fixable how about the STP stuff help? how about spark plug change?

 

valve lash makes a ticking sound, bottom end problems make a knocking sound.

If it's a ticking type sound, I'd adjust valve lash before I started dumping in fix-all oil treatments. If ticking persists after adjustment, might be a bad lifter (warrants removal on intake to check lifters and cam lobes).

If it's a knocking, then yes, might look into adding a oil treatment.

 

pull out the spark plugs and read them see how worn they are and how the air/fuel is on cylinders you think may be the cause of the knock,If the STP stuff you are talking about is that real thick stuff you add to the oil ya it will work im just use to using the lucas any auto part store will have it here is a link
http://www.lucasoil.com/pages3-2/FAQ this stuff will quite down any rod knock if that's the problem it will also extend the life of your engine i use it in diesel trucks

 

check your timing,could be to advanced,causing detonation

 

Could be a rattle or exhaust leak too. If it's only at start up it could be a drain back valve too. What's your oil pressure gauge telling you?

 

i think its a knock but it still has its kick it can put you back in your sea cause of the mods

 

retard the timing a lil 2-4 degrees,and see if it gets better if not turn it back,mark on dist shaft and intake with sharpie before you turn it so you can have a referance point,

 

a lot easier to slap in 8 gallons of premium fuel

8 gallons times 20 cents per gallon difference vs the cheap stuff= $1.60 extra cost

 

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See if you have a drippy injector