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[amba]

I have noticed that I appear to have a "hissing "noise from the plenum area and engine "hunts" alittle on tick over.Can anyone advise me of the part number of the seals from plenum to manifold as when I have it all in bits I want to replace anything that may be causing issue.  

[Bent valve]

 I Have had a few v6 omegas, and they have all made a hissing sound from the plenum area on tickover. at first I thought this was a plenum air leak but no amount of resealing would change the tone of the hiss.
In the end I decided that it was just general induction noise!

[Entwood]

Give a light spray around the area while the engine is running with carb cleaner. If the hissing note/engine note changes then the leak is in that area (the highly flammable carb cleaner has been sucked in and burned). This helps to pinpoint any leaks.

Afterwards wipe the engine down with paper towel.

Result... diagnosed air leaks and a nice clean engine ..  

[M0T0RVATE]

I had an airleak where EGR joins plenum, caused fast idle and you could here it too...
There was no gasket !

Check this too, when you take it all apart...

 

[amba]

I will get a can of carb cleaner in morning and have a spray..just a bit concerned around exhaust manifolds ?..am convinced that it sounds like hissing from plenum and knowing the number of times it has been off and on over the last 2 years thought the plenum/manifold o rings might be worth changing.

[jjleonard]

Pop the ecotec box off the top of the plenum (follow the instructions in the breather clean guide here) and check the state of the seal between the ecotec box and the plenum - it's a circular seal with a raised central bar.

If that seal is missing or damaged, you'll get the hissing, and the rough idle as the fuel / air mixture is incorrect.

VX part code for the seal is: 90467543.

HTH.

I speak from experience - it happened to me!

[Pedro]

I had an airleak where EGR joins plenum, caused fast idle and you could here it too...
There was no gasket !

Check this too, when you take it all apart...

 

My first place to look - had it myself!

[amba]

I know the eco brether to plenum seal is intact as that was replaced just after christmas whe i last did breathers...unsure about gasket from egr to plenum though..will have a look there as only gasket i recalled was metal one under actual egr valve,not from the metal manifold...will try the carb cleaner trick.

[tunnie]

also try pushing down on the plenum firmly at each corner, see if the idle or noise is affected. if it is, the 6 o rings on the inlet manifold could have gone hard

[Marks DTM Calib]

The breather bridge will always cause a light hissing on idle as there are two small drillings for the breather function associated with clsoed throttle.

When the crank case gases pass through these small holes then you get a light hiss noise.

I actualy listen for the hiss, if its not there then the small breather/breather holes are normaly clogged!

I looked at a car yesterday evening for somebody and it had excessive hissing....I suspect a damaged or misisng seal.....the owner is going to sort it!

[amba]

I will try your advise Tunnie...I had also thought maybe the 6 rubber o rings had gone hard..the plenum has been on/off numerous times in last 2 years and I have never replaced them.
Thanks also for your advise Mark...am sure all is very clean in the breather area just think the hissing is slightly louder than vere heard before..hence concern about air leak

[Marks DTM Calib]

I will try your advise Tunnie...I had also thought maybe the 6 rubber o rings had gone hard..the plenum has been on/off numerous times in last 2 years and I have never replaced them.
Thanks also for your advise Mark...am sure all is very clean in the breather area just think the hissing is slightly louder than vere heard before..hence concern about air leak

The 6 O rings will be fine....unless miss fitted and the idle would be shite if that was the case.

The ideal would be to do a vac test.

[djdaveyp85]

Pop the ecotec box off the top of the plenum (follow the instructions in the breather clean guide here) and check the state of the seal between the ecotec box and the plenum - it's a circular seal with a raised central bar.

If that seal is missing or damaged, you'll get the hissing, and the rough idle as the fuel / air mixture is incorrect.

VX part code for the seal is: 90467543.

HTH.

I speak from experience - it happened to me!

That was my problem! Seems to be really common! Easy fix, cheap part, just need a screwdriver and some torx bits!

[jjleonard]

Pop the ecotec box off the top of the plenum (follow the instructions in the breather clean guide here) and check the state of the seal between the ecotec box and the plenum - it's a circular seal with a raised central bar.

If that seal is missing or damaged, you'll get the hissing, and the rough idle as the fuel / air mixture is incorrect.

VX part code for the seal is: 90467543.

HTH.

I speak from experience - it happened to me!

That was my problem! Seems to be really common! Easy fix, cheap part, just need a screwdriver and some torx bits!

It does seem to be common - mine was thoroughly rotten and fell to bits as soon as I removed it. Even if they are OK, being rough with the Ecotec box when removing it can damage it - and once it's broken, it must be replaced!