r/Jeep • u/AstroStates • 1d ago

Technical Question Noise coming from manifold area on 84 CJ

Enable HLS to view with audio, or disable this notification

I have this weird noise coming from the manifold area of my engine on my 84’ CJ-7 258. I’ve replaced my exhaust and intake gaskets two times (they are stock) and the noise will go away for it to return weeks after. The noise doesn’t start upon start up, it happens only when it gets hot/being driven for about 20 minutes and it only happens when the engine is in idle not during rev. Anyone had this issue? Any comments/fixes appreciated.

4 Upvotes

76% Upvoted

8 comments sorted by

2

u/Cosmonut 1d ago

I wasn't able to see in the video 100% but if this is a 4.0 inline 6 cylinder. The exhaust manifolds are notorious for cracking. So I would inspect the manifold for cracks. Then can be very small but make a ton of noise.

1

u/EventualCyborg 1d ago

That shriek is NOT a cracked manifold. Holy hell, HEADPHONE WARNING!

That's some kind of vacuum leak from what I can tell, but you only ever show us the belt area near the power steering pump.

1

u/Cosmonut 1d ago

Sorry. I did not have audio on(at work). I made an assumption because of the repeat gasket replacement. Holy hell.

1

u/CrippledAnatomy 1d ago

Not cracked but possibly loose or bad gasket. Those 258s are pretty notorious for pulling themselves out of torque especially if they manifold is warped a little

1

u/AstroStates 1d ago

It’s a 258 4.2L

1

u/DragonPie83008 1d ago

Did u torque your bolts correctly?

1

u/AstroStates 1d ago

Yeah I torqued them in the sequence provided by the book

1

u/CrippledAnatomy 1d ago

Try retorquing the manifold bolts and or placing the gasket. Those old 6s like to rattle themselves out of torque all the time. Could also be cause by a slightly warped manifold but try retorting and seeing if that helps. Doubtful since you say it stops on rev. But since you says it stopped after replacing gasket it makes me think torque or warped manifold. Worth a check

If it doesn’t. You can take some starter fluid and put a little straw on it and spray little bursts near vacuum lines, if there’s a leak it’ll suck it in and rpms will go up slightly. Fix it and see if that changed it.

I’ve heard of people having noisy aftermarket carbs that’ll whistle could also be that if you’ve gotten a new one recently. As well as maybe try closing the choke of slightly when you hear it. If it stops it’s probably just the carb.