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
