2007 2.1 petrol. I have had my intake manifold off 3 times recently, trying to trace a vacuum leak (car engine missing on acceleration at low speeds). It runs perfectly at all other times. I have detected a leak right at the inlet manifold joint at the front, right hand, intake manifold joint, by using 'Start Ya *******' and having the engine miss when spraying right only at that position. I have just changed all gaskets (twice) and have ensured cleanliness of both joint faces.
Could it be that the manifold has a slight warp in it? Could I use a very thin layer of silicone on (say) the manifold face, hoping for a seal? I don't want it to get worse?
The silicone I have on hand has a top temperature use up to 150 degrees C. I doubt that area gets to a higher temperature, but any other advice would be appreciated. TIA

 

Are you detecting the leak between the intake manifold and the lower intake manifold .......air getting past one of the six upper intake seals?

If so, did you have one of the brass inserts seize and pull out of the plastic lower intake manifold at some stage when you were removing the upper intake manifold?

Could be that when you reinstalled the brass insert you didn't quite seat it low enough and the intake bolts are now unable to pull the upper intake down far enough to compress the intake gaskets .

 

Good suggestion, H2, but even though I did have 2 of those bloody things strip, they were the 2 next to each other at the other end, front - the usual ones. I glued them in and ensured they were well pressed down to normal level, by partly screwing in the bolts and pressing the nuts well down. I'm buggered if I know.... All bolt are now set to 10nm (about 7.4 ft lbs). Thanks for your suggestion.

 

If I had a vacuum leak and did not know, where, I would use a DIY smoke tester:
Baby-oil and an old rag in a jar, put on fire and a tube into the jar feeds air on demand (air gun) from the air-compressor and the tube out of the jar feeds airtight into a suitable position of your vacuum system. I have build one of those smoke-testers myself, and I found a few leaks with that on the air-intake side of my Fairlane, which was the reason as to why I did have issues, when driving on LPG (liquid petrol gas). There are tutorials, how to build what I described here on youtube.

 

Yorta2,

I suggest you reach out and PM Grant Francis.
I think some time ago he had a similar problem and felt that his intake manifold had distorted.
Worth an ask to see what he found, how he measured it and what he did to rectify.

 

H2, I have been thinking about your suggestion and realise that, even though the brass nuts that I inserted are at the opposite end, it could be that the previous owner may have replaced one up at the left hand end of the engine. I never thought to look at each of them and, even though the one on the from side is a long bolt that bolts into metal, it could be the culprit. I may have to pull the manifold once again and check. Great help!

 

Thanks Peter, but I know where the leak is, and don't know why.

 

My findings, way back.
I must update that thread, but Medical shiiit has taken precedence, sorry guys.

Look at the rubber/plastic spacers that go on the bolts..
They dictate how hard the manifold is "pulled down".
Age and heat (12/09 build) had mine less than pliable, AND, the thought that they had shrunk some also played on the brain. Having me think that this would NOT have the manifold being pulled down to sufficiently crush the seal below. NO MATTER how tight you do those bolts, the actual crush length is set by the spacers, and the rubber top flange.

I drank some beer, and thought of things.

Found some 3mm thick fibre washers that slid over the lower bit of the rubber thing, and sat nicely against the underside of the top flange.

Fitted the washers one bolt at a time, and noticed the manifold compressing ever so slightly. Finished, started the beast, sprayed the spray, NOTHING. Ran it till the fans started, sprayed again, NOTHING.

That was a long time ago in Forum time, and I have had no issues since.

I did check the manifold for warp, nope, all good, hence the beer and the above fix.

Since then I have done the same with the 3ltr S Type, and that annoying stumble sometimes is gone.

 

Excellent suggestion, Grant. Last time I took the manifold off, I wondered about the rubbers, so I swapped them about, swapping the larger 2 rubbers directly and the others randomly. It made no difference to the leaking. However, I didn't have the beers to assist in my thinking. I think you may have found the issue (but I have been wrong before). In a week or so, when I get the time to remove the intake manifold once more, I will try your suggestion. In the meantime, I will remove one bolt/rubber and find some fibre washers to insert. Thanks again for your advice. By the way, I can now remove that manifold, leaving the throttle cable and cruise control cable connected, in about 20 minutes, so it's easy now.