Re: '98 A6 2.8 won't start- mechanics are at a loss...

[Tom Nas <tnas@euronet.nl>]

quk@isham-research.demon.co.uk (Phil Payne) wrote:

>> All systems check out, no fault codes. Fuel and spark verified, timing belt
>> OK and not jumped a tooth. When you start it, it turns very quickly as if
>> there's no compression (which is OK when tested, BTW). Not even an attempt
>> to start, nothing.
>>
>> My first impression: plugged exhaust/cat. Any other suggestions?

I was hoping for a reply from you, Phil...

>Oil overpressure.  Attach a manometer-style gauge in place of the G10
>oil pressure sensor and compare base engine oil pressure with nominal.

...and you didn't disappoint me. Called my mechanic friend, he got very
excited as he ran over the symptoms and checked them against your theory.
There is an auto-shutdown in these engines to protect against high oil
pressures, and this is consistent with your theory.

>(Excess pressure causes higher than normal flow into the hydraulic
> lifters.  This becomes extreme as engine rpm increases, expanding
> the lifters and dumping compression - engine spins like a turbo.)

We think you're on to a winner, Phil. Your theory will be tested tomorrow...

On my next visit to the UK, I'll stand you a few rounds.

Thanks a lot!

Tom