Boost levels should be checked on a good, quality, aftermarket boost gauge - do not rely on the stock turbo boost gauge.  Stock boost levels are 5.5psi for 1986-1988 Zenki FC3S, and 7.5psi for 1989-1991 Kouki FC3S.


There are basically 4 modes of failure of the turbocharger:

Excessive oil in turbo compressor section
Splitter pipe and intercooler inlet hose removed.
Notice oil in intercooler inlet (yellow arrow).
Carbon seal on compressor backing plate most likely damaged.
First, internal oil seals on the turbocharger are damaged.  Initial signs of this type of failure are traces of blue smoke out of the exhaust under boost.  This failure can be easily confirmed by removing and inspecting the inside of the intercooler hoses (intercooler inlet hose is easiest to access) for signs of oil.  Note:  trace amounts of oil film is acceptable.
Symptoms:  blue smoke from exhaust under boost
Causes:  age and wear-and-tear; possible abuse (i.e. - overboosting)
Fix:  turbo rebuild - seal kit and labor
Possible prevention:  keep boost under 15psi (1bar) on the stock turbo

Second, excessive play of the wheel and shaft assembly will cause contact of the wheels into the compressor and/or turbine housing.  You can check excessive play by removing the black, rubber turbo inlet duct and accessing the turbo compressor wheel.  Check axial play (in and out) and radial play (side to side) for housing contact.  Note:  a small amount of radial play is acceptable, as long as it doesn't contact the housing.  Axial play should be close to nil - any contact with the housing and it's a sure sign of of a bad turbo.  Spinning the wheel by hand should be smooth, with no signs of dragging or scraping.
Symptoms:  loss of boost; excessive turbo noise under boost
Causes:  age and wear-and-tear; possible prior bad servicing (i.e. - rebuild) of turbo; abuse (i.e. overboosting)
Fix:  turbo rebuild - possible replacement of compressor and/or turbine wheels, center shaft, and bearings
Possible prevention:  keep boost under 15psi (1bar) on the stock turbo; insist rebuilds and servicing be done with balancing

Third, catastrophic damage to turbo wheels due to debris shooting through turbo during operation.  If you're running no or very little filtration through the intake, this can cause damage to the compressor wheel.  Even minute particles of dirt can pit and damage a compressor wheel spinning in excess of 100,000RPM!  A blown engine that has eaten an apex seal can also throw pieces of the damage internals out the turbine side of the turbo - this almost guarantees damage to the turbine wheel.  You can sometimes see obvious signs of damage to the wheels when pulling the turbo inlet duct on the compressor side and the downpipe/pre-cat on the turbine side.  There is not way to absolutely verify damage to the wheels except for removal of the turbo from the engine and a total teardown to inspect the internals.
Symptoms:  loss of boost; excessive turbo noise under boost
Causes:  little or no air intake filtration; blown motor
Solution:  turbo rebuild - minimum, replacement of damaged compressor and/or turbine wheels
Possible prevention:  always use a good air filter - never run without an air filter

Fourth, internal damage to the turbo oil bearings due to neglect or abuse of proper oil maintenance.  If the oil and oil filter was not change periodically, oil lubrication is decreased, causing damage to the turbo oil bearings.  Also, if you shut the engine off after hard, turbo boost, this can cause oil "coking", where the liquid oil cooks into hard, abrasive particles that can score the oil bearings.  Note:  the stock turbo is water-cooled and minimizes oil coking.
Symptoms:  loss of boost; excessive turbo noise under boost
Causes:  oil change neglect or inferior oil and oil filter used
Fix:  turbo rebuild - minimum, replacement of turbo oil bearings
Possible prevention:  proper oil and oil filter changes with quality oil and oil filters; idle down motor after hard boost, either manually or with an automatic turbo timer



Questions?  Comments?  Send mail to:  reted@fc3spro.com

12/26/2003