darcher93
As luck would have it, I have recently come to acquire an S40 T4 in the more or less debatable Swedish cult-hero colour of faded yellow. I managed to hook up a boost gauge to it and that's when I made some interesting obervations to the overall performance of the car. During idle, the car is making 1 psi. Now, it is my understanding that during idle, the system should more or less be creating a vacuum. So I am kinda left confused.
With the boost gauge hooked up, I took the car around the block a couple of times to give it a test run. The maximum boost pressure I could attain was 4 psi. The boost came on after 3000 RPM and would climb to 4 psi close to red line. Unless I am mistaken, the T4 should be building close to double the pressure from factory. I have checked most of the hoses and they appear okay.
Now, this is the part where my expertise is lacking. Could it be that I have missed a split hose and that there is a huge leak? OR could it be that the CBV is pooped?
jamesinc
At idle there's no way you'd be making 1psi, it should be like 15 inches of mercury vacuum (i.e. significant vacuum)
egads (she/her)
Where is the gauge hooked up to?
darcher93
The gauge is hooked up to the pressure side of the turbo and out to the BCS.
darcher93
Update. After doing a bit more research, I've plumbed the boost gauge into the line running from the throttle body and the CBV. On idle, the gauge reads approximately 18 inhg. Under WOT, the gauge gets up to about 1 psi. Thoughts anyone?
Ex850R
Adjust the waste gate lever to correct pressure. Or length if you don't bodge up a pressure adjuster tool, instructions are out there, mvs maybe.
jamesinc
Okay sounds like your gauge is now hooked up correctly. It'll either be a misadjusted wastegate, or a blown CBV diaphragm (or both). Both are easy enough to check.
darcher93
I'll have a look tomorrow. Fingers crossed it is just the wastegate that needs adjusting.
darcher93
Update. I pulled the heat shield off today and made an external inspection of the wastegate arm. Seems to be all okay. Pin still attached. I shortened the wastegate arm back a couple of full turns. then took it for a drive. Slight increase in power but nothing too noticeable. I then shortened the arm back all the way. Managed to build up about 5 psi but nothing more. Does anyone know what pressure the factory should be running? I feel that there is something else that could be casuing some issues. I will pull off the CBV at some point and have a look there.
jamesinc
The CBV diaphragm being damaged or the spring being worn and sagging are both fairly common issues and the CBV is easy to access (if memory serves) so worth checking.
darcher93
Where is a reasonably inexpensive place to source a CBV from? Or possibly a backing plate?
Ex850R
Cut your own plate to block off, pop in a blow off somewhere.
darcher93
What is the effect of just putting in a backing plate with no blow-off valve?
timbo
Vl turbo levels of dose/compressor surge
jamesinc
darcher93;c-144456 wroteWhere is a reasonably inexpensive place to source a CBV from? Or possibly a backing plate?
eBay. It's a TD04 right?
https://www.ebay.com.au/itm/Compressor-Housing-Blow-Off-CBV-Rebuid-Kit-VOLVO-SRT-4-TD04-TD05-Turbo-K5T09671/282008969729
Philia_Bear
T4 turbo is electronicly controlled isn't it?
timbo
Philia_Bear;c-144471 wroteT4 turbo is electronicly controlled isn't it?
Probs turbo control valve
jamesinc
That's true... You could always try pulling the vac hose and freeboosting... Just don't screw up ?
darcher93
I believe it is a TD04. If I was to pull the hose from the wastegate actuator, what would be the impact? Would the wastegate not open up? Would there be no boost? Would there be a vacuum leak from the wastegate hose I've just pulled off?
jamesinc
If you disconnected that hose, the wastegate would never open and you'd freeboost (i.e. there'd be no limit to how much boost the turbo can generate, so one misstep with the throttle and you'd potentially blow the engine up). Definitely do not drive it like this unless you are specifically testing whether the turbo boosts up to factory levels, and you've got a good boost gauge hooked up.
If the TCV is the issue, you can, as a temporary fix, just bypass it and run a vac line straight from the manifold to the wastegate actuator. This will give you boost up to the wastegate's stock setting, which is like 5psi, but I think a dead TCV will more or less be acting in this manner anyway.
