Test

Fuel pressure test is done engine off and by operating only fuel pump. Attach pressure meter just before fuel rail and connect two terminals on pump relay socket. Stock 745i turbo pressure is 2.5bar, anything else is because faulty or replaced parts. Low pressure is symptom off faulty fuel pump or pressure regulator. High pressure is caused by non-stock or crushed regulator. On stock engine high fuel pressure is for worse fuel economy, nothing else. Pressure regulator operates by intake pressure, vacuum decreases pressure and boost increases it.

Compression test gives good information on engine mechanical condition. State of head gasket, valves and piston rings follow up. Tracking causes for low compression in specific cylinder needs detailed testing, meaning compression build up as engine turns and measuring blow-by. According to BMW stock turbo compression should be between 8 and 9 bars. Rebuilt engine with Total Seal rings turns up to 10 bars. When measuring compression remove all spark plugs and white main relay, crank engine throttle wide open. Always adjust valve clearances first.

Turbo shaft test for play is done on compressor side. Look for scuffing/pitting on compressor housing and wheel itself. Test shaft by hand for excessive play. Some radial play in turbo shaft is always present, also on rebuilt unit. If there is doubt for burning oil and spark plugs are supporting this, remove and drain charge pipe after turbo for oil. Blue exhaust smoke is also telltale. Plugs in general should have ground electrode color similar to grey or light brown and insulator nose clean white. When using additives like lead substrates in fuel plugs may discolor.

Front wheel bearing play can be tested by rocking top of wheel sideways. There should be no loud clunking noise or notable play. Bearings are tapered and bearing play is adjustable. Remove wheel, center cap & pin and retorque crown nut as instructed in torque values page above. Spacer underneath crown nut has slot for trial. When bearing  is torqued and set, spacer should move quickly and without resistance. Loud bearing  noise in relation to driving speed is likely coming from front wheel bearings. Rear bearings are fixed and quite heavy duty for application.

Install boost gauge to test boost pressure, it should top 0,4-0,5 bar. Good place to connect is between HVAC line to manifold. In low and medium power only 0,2 bar boost is used, solenoid valve is open and not in use. High power or in acceleration solenod closes in pulses and decreases amount of control air to wastegate and boost raises. Manifold pressure is read constantly by computer and boost pressure is adjusted by solenoid as required. When solenoid is dead it leaves control line open and limits boost. Check solenoid valve, it should click when fed voltage from battery.

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