End play should be 0.001 to 0.003 inches. Up and down shaft movement should be no more than 0.003 to 0.006 inches.
What is turbo boost cut free#
A dial indicator can be positioned against the shaft hub to check for bearing free play. To check bearing clearances, there's usually no need to remove or disassemble the turbo. There's no way you can rebalance the rotating assembly, so if there is any indication of damage, the damaged parts must be replaced. The turbo may still spin freely, but the imbalance will prevent it from reaching maximum rpm and eventually pound the shaft bearings out-of-round. 001 oz.! A broken blade, worn blades or even nicked blades can be enough to throw the assembly out of balance. Most automotive turbocharger wheel assemblies are balanced to within. A turbo is a very delicately balanced assembly. Other problems to watch for are cracks, nicks or chips in the turbo wheel blades, and/or "eroded" (worn) blades. If it doesn't turn freely, repairs are in order. You should also spin the turbo by hand to feel for any roughness or binding. Any sign of scraping on either the turbo blades or the housing means the bearings are shot and the turbo needs to be replaced or rebuilt.
The best way to check for bearing problems or contact between the housing and turbo wheels is to remove the intake or exhaust plumbing from the turbo (which ever is easier) for a peek inside. The added friction prevents the turbo from spooling up normally, reducing the turbo's speed and effective boost delivery. If there is excessive play in the shaft bearings, the shaft will wobble allowing the wheels to scrape against their housings. Turbos spin at speeds that are often in excess of 100,000 rpm. One of the most common causes of poor turbo performance is bad shaft bearings which often results in rubbing or binding between the compressor and turbine wheels and their housings. A lower vacuum reading means you either have excessive backpressure in the exhaust system, an air leak somewhere in the intake system below the throttle (check the turbocharger hoses for leaks or loose connections), or a vacuum leak in one of the many hoses or accessories that tap off the manifold.Īssuming the engine shows normal vacuum readings but the turbo shows low or no boost, the next step is to find out what is wrong with the turbo. A late model engine with no vacuum leaks or unusual exhaust restriction should show about 16 to 22 inches of vacuum at idle. If the turbo fails to deliver any boost, or the boost pressure is more than a couple of pounds below what it should be, note the vacuum reading at idle. Factory boost setting may range from as little as 8 pounds to as much as 14 pounds, so compare your readings to whatever specs match your engine. Your gauge should go from vacuum to boost as rpms increase. Make sure the emergency brake is on and the transmission is in neutral or park, then rev the engine up several times by snapping the throttle wide open. The gauge must be teed into a manifold vacuum line, not a "ported" vacuum connection on the carburetor or throttle body. Most such gauges read vacuum in inches of mercury (Hg) and show pressure in psi. On vehicles that lack turbo instrumentation, you can get an indication of boost pressure by hooking up a vacuum/pressure gauge to the intake manifold. Try disconnecting the wastegate and working the linkage by hand to check for binding and proper closure.
What is turbo boost cut full#
But if it is hanging up and does not close fully, it will bleed off exhaust pressure from the turbine wheel and prevent the turbocharger from developing full boost. If the wastegate does not move at all, overboost and detonation is the usual complaint. Be warned, however, that excessive backpressure (often due to a clogged catalytic converter) can also prevent the turbo from developing its normal boost pressure. If it doesn't show normal boost pressure at full throttle (typically 9 to 14 PSI for many OEM turbo systems), better get the tool box. The easiest way to diagnose a weak turbo is to observe the vacuum/boost gauge or boost indicator light. Symptoms that may indicate a sick turbo include a loss of normal boost pressure and power, turbo noise, increased oil consumption and oil fouled spark plugs, or excessive exhaust smoking on diesel engines. But the time may come when your turbocharger no longer performs like it once did.Ī turbo's basic purpose is to create boost pressure, so when an otherwise strong running engine suddenly becomes anemic, it often (but not always) means turbo trouble. The greater the turbo boost pressure, the more power the engine makes. Turbochargers increase Horsepower by pressurizing air before it enters the engine. Turbocharger Diagnosis & Repair by Larry Carley copyright 2019
What is turbo boost cut manuals#
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