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Humming and pressure from exhaust/engine with ignition off

Tookey_87

Trainee
Joined
12 May 2013
Messages
77
I started my car tonight after it has been in storage for a few months and after a few mins of it running I turned of the ignition but when I got out I noticed there was a humming sounds from the back and when I put my hand over the exhaust exit on the cat pipe ( mufflers removed) there was slight air flow that stopped as soon as I blocked it the started again. Do anyone know what this could be?

Cheers
 
Probably boiling off condensed water

One of the main reasons to avoid short journeys (AKA short running times).
 
GT4 said:
Probably boiling off condensed water

One of the main reasons to avoid short journeys (AKA short running times).

That's great thanks I couldn't for the life of me think what it was.

Cheers
 
I would think that the noise was the air injection pump which runs after a cold start to reduce emissions - hence air coming out of exhaust.
 
SAI on a 3.4 would be rare on a UK model.

Tookey, does you car have this in the left hand corner (large black cylinder below coolant header tank):

996engine.jpg


If it does, repeat your test, but this time put your hand on or ear near the SAI to determine it is running.
 
My 996.1 has the SAI but it is one of the last made before the 3.6 was introduced. I did not realise that this is unusual on a UK car.
 
Only the run-out MY2001 3.4 M96/04 blocks ran SAI in the UK.

The 3.6 of course had a completely new DME and VarioCam Plus to help deal with new emission regs.

They are a pain in the bum for the barely 90 secs they are designed to run on cold start-up.

An inheritance from the US requirements.
 
GT4 said:
SAI on a 3.4 would be rare on a UK model.

Tookey, does you car have this in the left hand corner (large black cylinder below coolant header tank):

996engine.jpg


If it does, repeat your test, but this time put your hand on or ear near the SAI to determine it is running.

Yes it does have the air pump below the coolant header, my car is registered in 2001 so sound about right then by what you are saying

Cheers
 
Well, you can do the SAI test now (when it next over-runs)

Must be just before 996.2 change over.

Yours may well be a 996.1.5 - does it have electronic boot and engine deck-lid release too?

Those are the rarest.
 
GT4 said:
Well, you can do the SAI test now (when it next over-runs)

Must be just before 996.2 change over.

Yours may well be a 996.1.5 - does it have electronic boot and engine deck-lid release too?

Those are the rarest.

Yea it does, it was registered on the 16/10/2000
 
:thumb:

Probably the biggest downside to the M96/04 block is that it isn't X51 compatible.
 
GT4 said:
:thumb:

Probably the biggest downside to the M96/04 block is that it isn't X51 compatible.

What's included in the x51? Guessing it's only for the 3.6?
 
Nope, 3.4 too (M96/01, M96/02)

If you are wondering where the M96/03 went, that was the entire 996.2 3.6 Carrera run.

The 03 was already in development when the emissions bombshell required a last minute 04 stop-gap edition of the 3.4 to be made to allow it to still be sold.

Some X51 info here:

http://911uk.com/viewtopic.php?t=60293
 
GT4 said:
Nope, 3.4 too (M96/01, M96/02)

If you are wondering where the M96/03 went, that was the entire 996.2 3.6 Carrera run.

The 03 was already in development when the emissions bombshell required a last minute 04 stop-gap edition of the 3.4 to be made to allow it to still be sold.

Some X51 info here:

http://911uk.com/viewtopic.php?t=60293

That's great thanks
 

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