454s and exhaust leaks (maybe)

[Rockfish39]

OK.
Im a little stumped on this one :eek: . Wife's '89 Suburban has a Gen-IV BBC in it. Before the engine reaches full warm up, it sounds just like it has an exhaust leak on the right side. Once fully warmed up, the sound goes away. OK, here is a list of the components that were replaced. AIR tubes on right side. Exhaust manifold on the right side, donut gaskets both sides. Still the same problem. Thermal expansion is obviously tightening something up, but what???
Can the "Y" pipe joint at the converter be the culprit??? :scratch :scratch
Surely one of you guys who has a big C-K Chevy has encountered a similar problem.

Thanks for your help in advance!!!

Rock :cool:

[Dond409]

Exhaust manifold could be cracked again. It is a problem with these motors.

[fatride]

You know, I had that problem with a 84 K10 pickup with a 305 in it. Turns out it was the vacuum pot on the right side that controlled the combustion air to the air tubes. it was a little silver can that controlled a valve on the exhaust manifold. This can was hooked to vacuum and would open or close with engine ( water heat ) Drove me crazy for months trying to track it down. Fix was a small plastic check valve or vac delay in the vac line that ran to the pot. Hope this helps. :?

[oldskydog]

I think the egr valve can do that too if it sticks.

[Rockfish39]

You know, I had that problem with a 84 K10 pickup with a 305 in it. Turns out it was the vacuum pot on the right side that controlled the combustion air to the air tubes. it was a little silver can that controlled a valve on the exhaust manifold. This can was hooked to vacuum and would open or close with engine ( water heat ) Drove me crazy for months trying to track it down. Fix was a small plastic check valve or vac delay in the vac line that ran to the pot. Hope this helps. :?

Hey Fatride,
I think that you're onto something. :clap No doubt that this problem is related to WATER temp. That was puzzling the heck out of me :scratch

With very predictable and very reproducable results, the "NOISE" simply goes away when the temp guage hits about 180. Having burned my fingers and hands (about a million times over the past 30 years) I know that the manifolds, joints, CAT, and pipes get way hot, and much, much faster than it takes to bring the coolant temp up to 180.

So where is the silver can??? :eek: and how is it controlled by water temp ????

The other guys made great suggestions too, and I thank you for that!!! :bow


Rock :cool:

[fatride]

The can on my 84 was on the pass side exhaust manifold. It had a vacuum line running to a vacuum manifold that was standing behind the water goose neck
( themo housing) I can't remember the exact function but I sure remember the noise and the cure!

[DIV1RACER-2]

Rock

Don't think your 89 bb chev has a vacuum controlled heat riser, I'm pretty sure Fatride is refering that . The injected motors [ engines ] use water under the intake to provide the needed heat for drivability concerns.

I slug it out :takethat every day w/ these kind of problems ! i would look first at 2 things

1 If the ex manifold has a sheild on it it very well could be over heated & the cast iron is sagging or deterating some where under the sheild [ Have found this ]


2 Get a very bright flashlight or a long pencil light @ look a the manifold where it meets the ex ports . It very well could be leaking there till it gets warm enough to flatten out . Look for black soot . [ Have found this also ]

Another thing that is a possibility . crossover pipe may be a double wall pipe & causing some type of noise. cat conv / muffler or even intake gasket leaking at crossover even thought it should be blocked & not in use.


hope these ideas help!


Denny

[Rockfish39]

Denny,
Thanks for the suggestions. I did try the air tube valve trick that Fatride suggested...No workie... :cry Now I have to get into some more serious searching...

Rock :cuss