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Turbocharge Your MG Midget

Troubleshooting page 2

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Troubleshooting page 2

When diagnosing an engine performance problem on a turbocharger start with the basics.  Even if you think the turbocharger is at fault check the basics first, then consider the turbocharger.  The following are some of the more common problems encountered when trouble shooting turbochargers.

  • Excessive exhaust or blue smoke from the tail pipe and exhaust engine oil consumption will tell you first to check the air filter. A plugged air filter leads to a reduction in the flow of air to the turbocharger.  This can create a negative pressure area at the compressor seal, sucking oil past the seal into the intake air flow.  At the same time be sure to check the entire intake air ducting system for cracked hoses or loose clamps.  Continue past the turbocharger all the way to the intake manifold gaskets.

  • Check for correct oil drain and routing.  Oil leaving the turbocharger is by gravitational flow only.  The oil drain line must not be plugged and its angle of return should not be less than 35 degrees from vertical.  If a restriction in the oil return line exists, oil pressure can build in the unit causing oil to be forced past the seals.

The above was the course of smoking on my engine, basically my oil return line had a slight kink which forced the oil out of the exhaust.  Fixed it with new pipe and changed the oil outlet to a vertical out rather than the horizontal which you will have on the turbostandard.

  • Check the crankcase ventilation system.  Remember the basics, a malfunctioning crankcase ventilation system can increase crankcase pressure, forcing oil back into the air intake stream and into the turbocharger.  And don't overlook oil consumption from piston rings or valve seal problems.

  • If the vehicle has not been properly maintained the turbocharger center housing may be sludged or coked.  This condition will block oil passages and lead to turbo failure in short order.

  • If you have excessive exhaust smoke you can determine if the compressor seal or turbine seal may be at fault.  First check the spark plugs and examine them for an oil fouled condition.  If the compressor seal is leaking, all the plugs will be equally fouled.  If the plugs are burning clean and dry, the smoking condition may be caused by the turbine seal.

  • A common complaint on turbo charged vehicles is "the unit seems to be noisy."  Noise can be caused in several ways.  Be sure to check all ducting for air leaks both upstream and downstream of the turbocharger and for scaling or loose material.

  • Noise can be related to foreign object ingestion.  Foreign object ingestion in the compressor circuit can cause noise ranging from a high pitched whistle to a metal on metal sound.  Foreign object ingestion will become apparent as soon as any significant material is inducted into either the compressor or turbine wheels with the unit at speed.  Air or exhaust contamination can range from atmospheric dust and sand to valve train or engine fragments.  Foreign object ingestion will usually lead to bearing failures from the turbine wheel and shaft running in an unbalanced condition.

  • Noise can be related to bearing failure.  Bearing failure is usually due to inadequate oil supply, dirty or contaminated oil or excessive oil temperature.  Engine oil pressure provides lubrication and cooling to the shaft and full floating bearings.  If oil pressure for any reason is lost or restricted, serious damage will occur immediately.  For this reason it is important that the oil supply line be checked  regularly for signs of coking (every 30,000 miles).  Coke can form in the bends of the oil supply line, where it attaches to the turbo, from heat soak back when the vehicle is shut down.  Coking not only can restrict oil flow, but small pieces can brake off and become lodged in the bearing housing oil passages and drain annulus.  This can lead to catastrophic bearing failure due to oil starvation and is why the oil supply line must be replaced when installing a new turbocharger.

  • Excessive oil temperature caused by running the vehicle low on oil or a cooling system problem can also cause oil to coke in the bearing housing and lead to bearing failure.  Dirt or foreign material in the oil lubricating the turbocharger will quickly cause excessive wear and damage to bearings, shaft and bore surfaces.  This can easily be prevented by changing oil and filters at recommended intervals.  When oil contamination is present (depending on the size and type of contaminant) you may hear the sound of wheel contact with the housing as a progression of secondary bearing damage.

  • Lack of or low boost is usually stated as "my vehicle lacks power."  For this complaint first check the wastegate operation.  If the wastegate is not functioning or is improperly adjusted the vehicle may experience a lack of power.  To check the wastegate operation, tee into the pressure line to the wastegate with a pressure gauge and measure the pressure at which the valve opens.  Be sure to check for exhaust system leakage or exhaust system obstruction.  When replacing a turbocharger that passed a large amount of oil through the exhaust system, you must check for excessive back pressure at the turbo. 

  • Hot shut down is one of the worst conditions for a turbo.  Spinning at 75,000 rpm's and shutting off the ignition will leave a hot turbocharger spinning with no oil to lubricate the bearings.  Idle engine for a couple of minutes to allow cooler oil to circulate through the unit and allow the speed of the rotor assembly to slow before he shuts off his engine.  And most important, keep the oil and filter changed frequently.

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