Testing Turbocharger Wastegate & Blow-Off Valve

Using a "T" fitting, install pressure gauge in air pressure line that links air intake manifold with boost enrichment device on fuel injection pump. Install a tachometer that can be seen from driver's seat. Place pressure gauge inside vehicle where it can be easily read. Ensure hose is not kinked or pinched. Start engine and open gauge's valve, if equipped.
Road test using brakes or steep hill to hold vehicle at 35 MPH with throttle fully open, in 2nd gear with manual transmission, or in drive range 1 with automatic transmission.
NOTE: For safety during road test, it is advisable to have a helper read gauge or, if gauge is equipped with a valve, close valve at peak boost and record value later.
If testing on a dynamometer, hold the engine at 4000 RPM with throttle fully open. Transmission should be in 3rd gear with a manual transmission, or in drive range 2 with an automatic transmission.
CAUTION: To avoid unnecessary engine strain, road test or dynamometer measurement time should be limited to a maximum of 10 seconds.
Boost pressure should be 9.3-10.4 psi (.65-.73 kg/cm² ). If pressure indicated is greater, wastegate is faulty and turbocharger should be replaced. If maximum boost is lower, blow-off valve may be sticking open.
Disconnect blow-off valve outlet hose from intake air duct. Plug hose and secure plug with a hose clamp. Repeat test. Correct boost pressure at this point indicates that blow-off valve is faulty and should be replaced. Boost pressure still below specification indicates that turbocharger is faulty and should be replaced. See TURBOCHARGER BOOST PRESSURE table.