Volvo Owners Club Forum - View Single Post - S40 (New) Engine 2.0D :

Sidonas · Aug 26th, 2020, 15:40

Last update:

The specialist couldn't help me in any way, other than "you can leave the car with us and we will fix it but I'm not sure how much it will cost you". With that not being an option, I bought myself a vacuum meter to see what's the car doing when accelerating.

By using a T-shaped tube, I put it in between the vacuum pump and the TCV - 26 inHg delivered throughout the RPM range. I then put it between the TCV and the Actuator - it was jumping around a lot and I couldn't make out much except for the vacuum dropping to ~3inHg past 3.1k RPM. I also went for a ride with a disconnected TCV with ~6 inHg of vacuum applied to the actuator - the idea was to find out whether it is possible to get the turbo to boost to the desired value at 3000+ RPM. The turbo lag was horrible, however, at 4200 RPM it hit the desired value. This confirmed that the turbo is functional and can generate boost past 3000 RPM but the turbo control mechanism is out of order.

Then I wanted to test the actuator, so using the same T-shaped tube I connected it to a syringe and started applying vacuum. It started to move as soon as I applied even 1 inHg (i believe the spec is ~4 inHg) and hit the stop screw at ~16 inHg (spec 19-24 inHg). Since I had already replaced the TCVs and was sure that there are no vacuum leaks, this led me to believe that the problem lies in the actuator. However, there is very little space to work with, thus replacing and setting it up properly would require at least specialist tools if not a removal of the whole turbocharger.

Now the actuator is made out of two elements: a metal can with an arm that retracts while applying vacuum to it and an electronic turbo position sensor that tells the ECU how far down the actuator arm is retracted. I thought that perhaps it wasn't spooling up properly in the low end because the turbo position sensor was telling it that it is already 100% retracted when it was not. To move the sensor a little bit further back, I removed it and then replaced it in using a 1 mm gasket. This didn't change the low-end in any way, however, for some reason it fixed the high RPM boost drop-off (to confirm that this was not a coincidence, I also tried to remove the gasket and the car started to drop boost once again).

To test whether the turbo lag issue was indeed caused by the turbo control mechanism, I bypassed the TCV by connecting the actuator directly to the vacuum reservoir of the car (26 inHg stable). There was a very slight improvement in turbo lag but it might have even been a placebo. Additionally, yesterday I got to drive a well-working V50 with the same engine and noticed that is was way more powerful in the 1000-1600 RPM range. I now think that perhaps there is some other thing wrong with my engine and it just isn't generating enough exhaust gas to spool the turbo up at low RPM.

Aug 26th, 2020, 15:40	#4
Sidonas Junior Member Last Online: Aug 28th, 2023 13:55 Join Date: Oct 2019 Location: Kaunas	Last update: The specialist couldn't help me in any way, other than "you can leave the car with us and we will fix it but I'm not sure how much it will cost you". With that not being an option, I bought myself a vacuum meter to see what's the car doing when accelerating. By using a T-shaped tube, I put it in between the vacuum pump and the TCV - 26 inHg delivered throughout the RPM range. I then put it between the TCV and the Actuator - it was jumping around a lot and I couldn't make out much except for the vacuum dropping to ~3inHg past 3.1k RPM. I also went for a ride with a disconnected TCV with ~6 inHg of vacuum applied to the actuator - the idea was to find out whether it is possible to get the turbo to boost to the desired value at 3000+ RPM. The turbo lag was horrible, however, at 4200 RPM it hit the desired value. This confirmed that the turbo is functional and can generate boost past 3000 RPM but the turbo control mechanism is out of order. Then I wanted to test the actuator, so using the same T-shaped tube I connected it to a syringe and started applying vacuum. It started to move as soon as I applied even 1 inHg (i believe the spec is ~4 inHg) and hit the stop screw at ~16 inHg (spec 19-24 inHg). Since I had already replaced the TCVs and was sure that there are no vacuum leaks, this led me to believe that the problem lies in the actuator. However, there is very little space to work with, thus replacing and setting it up properly would require at least specialist tools if not a removal of the whole turbocharger. Now the actuator is made out of two elements: a metal can with an arm that retracts while applying vacuum to it and an electronic turbo position sensor that tells the ECU how far down the actuator arm is retracted. I thought that perhaps it wasn't spooling up properly in the low end because the turbo position sensor was telling it that it is already 100% retracted when it was not. To move the sensor a little bit further back, I removed it and then replaced it in using a 1 mm gasket. This didn't change the low-end in any way, however, for some reason it fixed the high RPM boost drop-off (to confirm that this was not a coincidence, I also tried to remove the gasket and the car started to drop boost once again). To test whether the turbo lag issue was indeed caused by the turbo control mechanism, I bypassed the TCV by connecting the actuator directly to the vacuum reservoir of the car (26 inHg stable). There was a very slight improvement in turbo lag but it might have even been a placebo. Additionally, yesterday I got to drive a well-working V50 with the same engine and noticed that is was way more powerful in the 1000-1600 RPM range. I now think that perhaps there is some other thing wrong with my engine and it just isn't generating enough exhaust gas to spool the turbo up at low RPM.