Re: Oil cap off kills car

[quk@isham-research.demon.co.uk (Phil Payne)]

In message <375138a8.36fe27c7@aol.com> PMStaples@aol.com writes:

> I have a 1988 90 Quattro, non turbo,10 valve, 5 speed. I am getting a rattle,
> knock from the engine at idle, low speeds. The car seems to run OK, but not
> great. While looking under the hood with the engine on, I took of the oil fill
> cap, and the engine died immediately.

It doesn't matter whether you have a turbo or not.  What matters is
whether the breather lines are connected to the air inlet before or
after the air mass sensor.  In your case, probably the latter.

Removing the oil filler cap just lets lots of air into the breathers.
If they connect _after_ the air mass sensor, then the mixture will be
weakened dramatically and the engine will stall.  On a properly set up
engine, even pulling the dipstick causes a stumble.

Being able to stop the engine this way, or not, is not necessarily a
problem in itself.  The issue comes with engines where:

a) The breathers are attached to the inlet _after_ the air mass sensor.

b) The engine _DOESN'T_ stop when the cap is pulled.

In this situation, all it tells you is that there is so much leakage
around oil seals, etc., that the mixture has been set to allow for a lot
of unmetered air.  This is a bad thing, because this bias in the setting
causes the mixture to be off at high loads.  The fix is expen$ive.

--
 Phil Payne
 Phone: 0385 302803   Fax: 01536 723021
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