S70 T5 Overboost

[Saxo Boy]

I have a 1996 S70 T5 that is overboosting very briefly on gearchanges to 15psi. The rest of the time it runs around 10-11psi which, I believe, is standard.

The overboost is only for a half second and it quickly settles back to 10-11psi. My questions are:

1) How big a problem is this? Is my engine likely to grenade?
2) If this is a problem that needs fixing, where do I start?

Thanks

[acshortt5]

If the car is an auto then that is normal as the boost spikes on gearchanges. Nothing to worry about.

If it's a manual then yes something is wrong.

[960kg]

Originally Posted by Saxo Boy

I have a 1996 S70 T5 that is overboosting very briefly on gearchanges to 15psi. The rest of the time it runs around 10-11psi which, I believe, is standard.

The overboost is only for a half second and it quickly settles back to 10-11psi. My questions are:

1) How big a problem is this? Is my engine likely to grenade?
2) If this is a problem that needs fixing, where do I start?

Thanks

I would worry about it as spikes can be dangerous.

I had this before i had a re-map and you must have a hose leak from somewhere around the compressor of the turbo to the BCS or back to the actuator diaphragm.

Because it leaks the boost will be high then the ECU corrects the boost back to the normal, not really ideal!!

[Saxo Boy]

Originally Posted by acshortt5

If the car is an auto then that is normal as the boost spikes on gearchanges. Nothing to worry about.

If it's a manual then yes something is wrong.

It's an auto

Why does it spike on the auto? What is going on that causes or necessitates it?

[960kg]

Originally Posted by Saxo Boy

It's an auto

Why does it spike on the auto? What is going on that causes or necessitates it?

You have a leak!

[Saxo Boy]

Originally Posted by 960kg

You have a leak!

The previous poster seemed to think this was normal for an auto

Does anyone have a diagram/photo of where I should be looking for such a leak? How do I test for such a think given that I can't create boost with my head in the bonnet to see where air is coming out!

[960kg]

Originally Posted by Saxo Boy

The previous poster seemed to think this was normal for an auto

Does anyone have a diagram/photo of where I should be looking for such a leak? How do I test for such a think given that I can't create boost with my head in the bonnet to see where air is coming out!

Why do you bring it to attention if you may think it is normal? You must be concerned.
If you think it`s normal then leave it.

You can check the hoses marked for leaks or just replace with Volvo ones £9 per metre which is sufficient.

[acshortt5]

You don't have a leak, this is completely normal for an AUTOMATIC transmission car.

Think about it, you don't lift off the throttle when it changes gear like you would in a manual on gear changes. That's the basic reason but I'm sure there will be a better, more technical explanation either somewhere else on the forum or on another site.

Edit: if you do replace the small diameter vac hoses then use Goodyear fuel hose as it's better and cheaper than getting the Volvo ones ;-)

[960kg]

Originally Posted by acshortt5

You don't have a leak, this is completely normal for an AUTOMATIC transmission car.

Think about it, you don't lift off the throttle when it changes gear like you would in a manual on gear changes. That's the basic reason but I'm sure there will be a better, more technical explanation either somewhere else on the forum or on another site.

Be practical......it doesn`t matter if you lift the throttle or not the ECU controls the boost to 9 or 10psi, if it has to correct it then there is a leak, full stop, end of story.

[Saxo Boy]

Originally Posted by 960kg

Why do you bring it to attention if you may think it is normal? You must be concerned.
If you think it`s normal then leave it.

I didn't think it was normal, which is why I created the post.

I was simply latching onto what acshortt5 was saying about the auto and desperately hoping he was correct