Vac leak - eliminated some, what’s left

[JimmyMc]

Morning all,
Trying to find a vacuum leak this morning to help with a lumpy tick over.
I’ve rigged up a test, without smoke, and can hear a leak. I’ve narrowed it down to the valve cover onwards (into the engine and not back toward the tb).
It doesn’t sound like it’s coming from the valve gasket or bungs (which are new). Sounds to be low down near the intake manifold bolts. Doesn’t seem to be dipstick related.
What else do I need to be checking?
Thanks in advance. A smoke test would be much easier, but haven’t got the stuff at the moment.
320i auto 1990.

[twright]

If this is an M20, there is an o'ring that is sealing a vent tube to the block from the intake manifold. It's tough to see and you have to take off the intake manifold to replace it.

[JimmyMc]

Thanks. Yes, an M20.
Does it often go? And is it just one at the top?

[JimmyMc]

Had a look on realoem and spotted a seal at the bottom but not the top. So could it be the bottom seal? It looks a bit oily down there around the spring.

[Brianmoooore]

The ETK diagrams are in no way an assembly guide. There's a flat washer (11) and an O ring (10) at each end of the tube, but only one spring.
They're not a common problem, but, like anything rubber, they harden with age and heat, and usually need replacing if disturbed.

[JimmyMc]

The ETK diagrams are in no way an assembly guide. There's a flat washer (11) and an O ring (10) at each end of the tube, but only one spring.
They're not a common problem, but, like anything rubber, they harden with age and heat, and usually need replacing if disturbed.

Thanks Brian. I’ll order a couple of seals. Can it be done without removing the IM?

[Brianmoooore]

. Can it be done without removing the IM?

Top one can be, but not the bottom.
Grease the O rings well, and tie the spring in a compressed state with a couple of small cable ties or thin wire. Once the inlet manifold is back on, cut the ties, and make sure the top O ring goes fully into place.

[paultv]

Matter of interest, did you check the little rubber bung attached to the underside if the TB? They have a habit of perishing and falling off.

Paul

[JimmyMc]

Matter of interest, did you check the little rubber bung attached to the underside if the TB? They have a habit of perishing and falling off.

Paul

Hi. It still seems to be there, and don’t think it was where the leak was coming from.

[JimmyMc]

In order to get a complete kit of parts, if I order 2 o-rings and the gaskets, should I replace anything else while I’m there or leave alone?

[Brianmoooore]

Nothing to replace as such, but a few things to check. You can open up the rubber boots of the plug and socket for the injectors, under the inlet manifold, and check for corrosion, you can check the rubber cap underneath the throttle body, mentioned above, and you can check the alloy elbows on the side of the throttle body are all firmly seated.
The inlet manifold gaskets themselves are a common source of air leaks. They become brittle, and a section of the gasket breaks away and gets sucked into the engine, leaving a small slotted hole. It often gives itself away by making a whistling noise under high vacuum conditions, but not always.

[JimmyMc]

So, stripped it down today and found this.
Looks like no o-ring and no washer at the bottom.
Covered in mastic. And a rubber boot at the bottom.
Do I need to replace the rubber boot at the bottom? Not seen that before.

[Brianmoooore]

No rubber boot there on any M20 I've ever seen. I think your car has been the victim of a first class bodger!

[JimmyMc]

My thinking exactly. Looks like it might be a ball joint boot.
Looks like I just need to get a washer.

[JimmyMc]

No rubber boot there on any M20 I've ever seen. I think your car has been the victim of a first class bodger!

Do I need a washer at the top and the bottom?

[JimmyMc]

Matter of interest, did you check the little rubber bung attached to the underside if the TB? They have a habit of perishing and falling off.

Paul

Having got the IM off, with the TB still attached, I had a look for the bung, and there doesn’t appear to be one. Just the body of the socket which is one piece plastic. Will be putting it all back on tomorrow.

[Brianmoooore]

Spigot wouldn't be visible in that pic. It's tucked in below the TPS, and very close to it.