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Engine question

What is this small air hose on the cylinder cover for? There is a round

1/2" hole in the cover with a rubber ring. A nylon fork in the hole branches in two directions. I sensed a whiff of petrol in the car and found that the nylon thingy had popped out of the hole. I put it back, but it didn't fit well as the rubber ring had become brittle; it needed replacement.

Today, I then replaced the rubber ring £2.90 . OK I suppose they have to store all and sundry bits for years and keep stock control. However, after I had replaced the rubber ring and everything was air tight, I started up and got check engine for a short while, then the idle raced up and down and eventually settled at the correct 900 rpm; after that no problems. It felt like the engine adjusted itself to the new conditions - can it really do that?

Reply to
Johannes H Andersen
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It is part of the crankcase ventilation system.

The small hose should connect to a small check valve and then on to the throttle housing. During low load conditions the low pressure in the throttle housing is used to evacuate gasses from the engine through this hose. The check valve will close when there is pressure in the throttle housing (when the turbo is providing pressure).

The large hose should connect to the suction side of the turbo and is used to evacuate gasses from the engine when the turbo is providing pressure.

This is an overview. The details vary between engine models.

A working crankcase ventilation system is vital for the engine.

A common problem. Just buy a new rubber ring.

Yes. You didn't tell us what engine this is, but the idle will be affected if the crankcase ventilation system is leaking. The leak will provide extra air into the throttle housing and the ECU has compensated for this by closing the idle control valve (older engines) or throttle plate (Trionic 7 engines). When you fixed the leak the ECU had to find out what to change to get the correct idle again.

Reply to
Goran Larsson

In message , Johannes H Andersen writes

Which engine? PCV valve?

Reply to
Peter W Watson

Does this apply the same to non-turbos? I have the hose running to the throttle housing but there is no check valve. How vital is it to have one?

-- Christian

1985 900 8V (non-turbo)
Reply to
Christian M. Mericle

No. The check valve is only required if the pressure in the air intake will increase above atmospheric. This can only happen with a turbo charged or supercharged engine. On a NA engine, the pressure will always be lower than atmospheric pressure.

Reply to
Grunff

Except when it backfires through the carb.... That's why there's a check valve in the PCV system on the V4 engines.

-- MH '72 97 '77 96 '78 95 '79 96 '87 900T8

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Reply to
MH

No. The goal is to locate a source of low pressure. For slow cars this is somewhere on the throttle housing. For fast cars you need two sources, somewhere on the throttle housing when the turbo is not providing boost and just before the turbo when the turbo is providing boost.

The check valve is only needed on turbo cars.

If the check valve is broken or missing the turbo will pressurise the crankcase. This is bad, very bad.

Reply to
Goran Larsson

I believe engine is B202S for MY 1993 9000 CSE 2.0 LPT

Reply to
Johannes H Andersen

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