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Volvo 940 lpt boosting low at barely 2 psi

posted by  SalvadorP on  Mon Apr 3 13:27 CST 2023
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I have a 940 wagon b230fk, manual. 510.000km, all maintenance/repairs done at volvo dealership until I got it from the original owner 2 years ago. Need help diagnosing low boost pressure.

I will describe the situation in topics:
- Installed boost gauge and it barely read 2psi. Don't remember vacuum value.
- Installed another boost gauge. Same boost reading. Vacuum at idle = 17-21 psi
- Checked condition of the bypass valve. Bypass Membrane looks completely fine.
- Checked condition of wastegate actuator arm. Wastegate arm is assembled and moving.
- Looked for vaccum or boost leaks with smoke test and brake cleaner. No leaks found. Brake boost check valve has some play. Fastened all clamps.
- Checked Turbo from the intake side. No play on turbo shaft. Blades spin freely and noiselessly.
- Installed MBC and increased pressure gradually but significantly 2 times. Same boost reading after pressure increase.
- Disconnected wastegate hose. Ran the car for a short time and cautious manner. Same boost reading

Observations:
- All engine gaskets were changed almost 4 years ago and 38k km ago. Visually they look fine. Brake cleaner on intake did not change rpm.
- Compression test 13 months ago had Cyl #1 - 161, Cyl #2 - 160, Cyl #3 - 162, Cyl #4 - 164
- Catalytic converter needs to be changed and might be clogged. It was changed 190k km ago in 2007 (oem)
- Car has a slight misfire at idle that I couldn't yet diagnose.
- Almost all vaccum hoses have been changed recently.

To do list:
- Compression test.
- Exhaust backpressure test.
- Check intercooler for leaks. Drain it???

Any ideas are welcomed. Thank you.
Salvador






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