The rattling noise is pinging. If it won't do it when you rev the engine in neutral, and it does it when accelerating in gear, it's pinging. Change the plenum gasket and you're good to go.

 

sorry, i just read your middle post where you had a mechanic tell you his opinion was a crank bearing.

if there's any way you have a mechanical knock from a bearing, then i would not waste money doing a plenum fix on that motor. if you're not sure, get another opinion from a professional mechanic. don't waste good money on an engine with a crank or rod knock unless you know what you're getting into, and your paying to fix it. DON'T GUESS on something this expensive.

 

when the truck is in neutral and i rev up to 2000rpms and keep it there, there is a knocking/pinging whatever it is, when im accelerating it happens again between 2000 and 3000 rpms, no noise at constant 60mph at like 1700 to 2000 rpms, can pinging be only at a certain rpm and unuder a certain load? this is really a tuff one for me, i can do the crank bearings but dont want to get in it if thats not the problem

 

i'm pretty sure if it was a crank or rod knock it would do it under any load

to me sounds like pinging

 

I agree with Maroon. With that said, I'd still hate to see you do a plenum fix on a motor with a bad crank bearing (if it indeed is that). Do what dhvaughan said and get another inspection to confirm or deny the notion of a bad crank bearing, then go from there.

 

USUALLY/sometimes, a simple way to eliminate pinging is to run higher octane gas. the higher the better (92-93-94), and if that's not enough, add a little, not too much, octane boost.

if the knock goes away, proceed with your plenum repair.

if the knock stays, you MIGHT have other problems.


edit - simple description.
http://monsterguide.net/octane-booster


more - if you use an octane booster, or racing gasoline, be aware not to use anything LEADED, such as Aviation Gas, or Lead Additive for older cars.

Motor Trend: What does lead do in a race gas? What about lead substitutes.
Rockett Brand: Lead in the form of "Tetraethyl Lead", sometimes called TEL, is an anti-knock compound. When TEL is added to gasoline, it raises the octane number and therefore reduces the chance for detonation. If you have a race engine with very a high cylinder pressure (due to a high compression ratio, a high boost turbocharger, a supercharger, and/or a nitrous oxide system) you may need a leaded racing gasoline.
Lead also acts as a lubricant, thus lead substitutes can be helpful in pre-1973 engines that do not have hardened exhaust valve seats; a lead substitute will help the seat from wearing excessively. If you have an older engine from the musclecar era, your best bet would be to have hardened exhaust valve seats installed when the heads are being rebuilt.

 

Did anybody catch this sentence in that article vaughan posted?

Compression ratio is, simply, the number of compression strokes the car engine’s cylinder goes through before the fuel is ignited.

Apparently my truck compresses the a/f mixture 9 times before the cylinder gets fired...

 

yeah, i was waiting for someone to catch that...
i knew that they meant "volume". figured every one else did too.
i always wanted a 9 cycle engine

the rest of it was pretty accurate

 

ok went to multiple shops, 3 mechanics said it top end noise like valves lifters rocker arms or push rods, and one said bottom end noise like crank bearings, can my plenum gasket make valves/lifters/rocker arms/push rods make noise due to a vacum leak?

 

wonder what a 9 cycle would sound like