S70 T5 Overboost

[acshortt5]

Originally Posted by 960kg

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.

Have you ever driven an auto T5 equipped with a boost gauge?

[Saxo Boy]

Originally Posted by 960kg

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

For someone non-technical...how do I check them for leaks? In other words how do I get some pressure through them without being on boost?

[Saxo Boy]

Originally Posted by acshortt5

Have you ever driven an auto T5 equipped with a boost gauge?

Playind devils advocate here....but how do you know the one you drove didn't have a leak too

[acshortt5]

Originally Posted by Saxo Boy

Playind devils advocate here....but how do you know the one you drove didn't have a leak too

Because I have been driving it for years, and still am, and I have replaced ALL of the pipework.

[Saxo Boy]

Any other auto owners with experience?

Once I figure out how to pressurise the pipework to check it I will give it a once over just to be on the safe side.

It would be a bonus to know this is normal and I don't have to identify and fix a problem.

[960kg]

Originally Posted by acshortt5

Have you ever driven an auto T5 equipped with a boost gauge?

I had the `95 Champagne coloured T5 for 2 yrs it was an auto with a separate guage and read no 15psi just the standard 9/10psi with smooth changes through out.

I now have the `97 V70 T5 manual and had to change the hoses and TCV as it overboosted to 15psi and then it was corrected to 10psi by the ECU and there was a very distinctive jerk at 15psi which was not normal.
I replaced the TCV and the hoses and was then back to normal 10psi

You don`t have to be superior or argue because you are a Volvo nutcase as we are all here to help

The OP posted as he thought he had a problem so if he still thinks he has then it is up to himself to do whatever he wants to do to keep himself happy.

At least at the moment he has two helpers instead of just one!!

[Saxo Boy]

I was just thinking about this logically in my head and have a theory on what is actually going on. I'd appreciate input on how close I am:

Assuming there is a leak and air is escaping from an otherwise sealed system, I draw the following conclusions... When I drive hard, the boost will rise to 11psi, as controlled by the ECU. However, to make this pressure the turbo will actually be working harder than it otherwise would because it has to make 11psi in an environment where pressure is being leaked away.

The cause of the of the brief overboost is the delay it takes for the ECU to react to the fact that the turbo is running away (when the boost builds again) and to peg it back to an artificially held 11psi. If my assumptions are correct, every time the car is on boost there are components (mainly the turbo) that are working harder than they would be without a leak.

^^^^^ How close am I? Is that what is going on?

Finally, anyone care to suggest a technique for finding the source of a leak?

[960kg]

Originally Posted by Saxo Boy

I was just thinking about this logically in my head and have a theory on what is actually going on. I'd appreciate input on how close I am:

Assuming there is a leak and air is escaping from an otherwise sealed system, I draw the following conclusions... When I drive hard, the boost will rise to 11psi, as controlled by the ECU. However, to make this pressure the turbo will actually be working harder than it otherwise would because it has to make 11psi in an environment where pressure is being leaked away.

The cause of the of the brief overboost is the delay it takes for the ECU to react to the fact that the turbo is running away (when the boost builds again) and to peg it back to an artificially held 11psi. If my assumptions are correct, every time the car is on boost there are components (mainly the turbo) that are working harder than they would be without a leak.

^^^^^ How close am I? Is that what is going on?

Finally, anyone care to suggest a technique for finding the source of a leak?

That is true what you say and it is called "spiking" the ECU does not let the boost go to 11psi it stops it going over 11psi, it is the turbo and associated parts that give the boost and those parts have failed because the ECU is reducing the boost a fraction to late so you get 15psi but if you do have a leak then the Turbo Control Valve is not doing it`s job by keeping the boost controlled as the leak may be on the TCV to actuator side which is past the control of it. You should have something like 5psi in 1st gear followed by about 8 in 2nd and then 10psi in 3rd and 4th as it changes up.
Because of the age of the car (my hoses were very black and crumbly) why don`t you just replace the hoses and also get a new TCV as i did then the boost is all controlled to protect the engine!

If you want to stop it spiking then you have to start somewhere!

[Saxo Boy]

Where is the cheapest place to source said parts?

I'll get it done, the car was only £1100 but it otherwise seems to be in pretty good nick and I don't want it letting me down.

[Jod T5]

Of course, the arguments on this thread are counteracted by the fact that the pre ME7 (turbo) ECM's (MY1999) do not have boost pressures reported back to them....

The older units do report issues such as throttle position and MAF sensor results etc... that give fuel cut (not electrical ignition note)....

I would give Andrew's opinion a little more credit than it appears it is being allowed....

Jod