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ABC's of Running High Boost, Long post
I sent this info to others on the list who were interested in doing
ECU Boost mods. I was asked to repost it to the main list as
it may be useful to others considering these mods.
I have added some new info as of late.
I thought I would comment on some of the problems that can come up when
one decides to run higher levels of turbo boost. The following comes from
my own personal experience and includes a lot of information that
other people who contribute to the main quattro email list have provided.
The following applies to the 10V I5 MC turbo engines (1991 FWD 200T
and the 1986-1990 model FWD 5000T's and 5000TQ's/200TQ's).
THE ABC's of Running High Boost
"BEFORE" you decide to do any Turbo boost mods to your car please read
the following. No one on this list who decides to do EPROM mods wants to get
inundated with phone calls or emails asking questions about your engines
problems that are caused by worn out/defective stock components. It
should be your responsibility (or your mechanics) to check out and
verify all the system components are working correctly.
Obviously a tune up, new plugs, fuel filter, air filter, oil change etc.
should done before stressing the engine with more turbo boost.
You need to make sure your engines various breather/vacuum hoses
and turbo intake and pressure hoses are in good shape. Leaks anywhere
in these hoses can cause lean or rich running and poor starting. Vacuum
leaks would typically cause lean running, pressure leaks after the turbo
could cause slightly rich running. It is NOT sufficient to just visually
look at these hoses without first removing them!
The large breather hose coming from
the side of the engine up to the valve cover typically gets rotten on the
inside part of the hose facing the engine block. The small T hose connecting
the two hoses to the valve cover also gets rotten from the oil mist flowing
through it and will crack on the back side. The other hose connecting the
intake boot to the valve cover should be removed and checked. The two small idle
stabilizer hoses should be removed and checked also as they can get
blown off from the pressure. Any of the smaller hoses connected from the intake
mainifold to the heater/AC system should be checked for cracks.
The valve cover gasket, the dipstick seal and the oil cap seal
should also be checked and can be a source of a vacuum leak. Even the
front and rear crankshaft seals along with the camshaft seal can be the
source of vacuum leaks (this is less likely) The rear crank seal will
sometimes "squeal" when the car is first started because it is leaking
and allowing air to be sucked past or because it has no oil on it at first.
Removing the dipstick with the engine running usually silences this "squeal".
Sometimes pushing in the clutch will also silence this squeal. (Pushing in
the clutch moves the crankshaft slightly) Ned Ritchie at IA published a tech tip
in the QCUSA quarterly newsletter regarding this problem.
The accordian style hose that connects the intercooler exit to the intake manifold
usually rots (from oil) and cracks at the bottom between the ribs. Remove and
check it. The turbo intake hose that connects to the metal pipe and the turbo exit
(pressure) hose going to the intercooler should both be removed and checked
as well. The later 200TQ's with the smaller K24 turbo have some "insulation
foam" inside this pressure hose going from the turbo to the intercooler and
sometimes this insulation will come loose and get blown into the intercooler.
Sometimes the hose clamps for these pressure hoses are just loose and under
high boost will leak.
You may also want to check the cold side turbo shaft for
excessive play and look for any metal shrapnel caused by worn turbo bearings
allowing the blades to rub against the turbo housing. The main fuel distributor
rubber boot should be visually checked for cracks with a flashlight and a
mirror especially around the edge where the large clamp holds the boot to
the fuel distributor opening. The decel valve located on the CIS air box
assembly (behind the fender) and large rubber hose going to the fuel
distributor rubber boot could also be the source of a vacuum leak. There
are also charcoal canistor purge valve(s) (late 89 has two) that should
be checked for correct operation.
The intercooler end cap seals can leak and you may want to install some straps
around the intercooler to hold it together under high boost. The internal
intercooler rubber seal that seals the internal upper and lower sections of the
intercooler should be checked when you remove the hoses from the intercooler.
You should look inside the intercooler and make sure this seal has not blown
out which would allow the air entering the intercooler to bypass the intercooler and
go straight into the intake without any cooling effect.
The fuel injector inserts that are screwed into the cylinder head may need
to be replaced along with the rubber o-rings sealing the fuel injectors. The
green Viton injector o-rings should be used instead of the older black rubber
ones that get hard and don't seal well over time. Leaky injectors can increase
the hot/cold starting times. Dirty/clogged injectors can cause poor low
end performance and uneven performance when cold. Intake valve carbon
deposits can also cause cold running problems as the carbon acts like a
sponge, soaking up the fuel at first. You should look at the back of the intake
valves when you remove/replace the injector inserts. With severe carbon
buildup some repair shops can use a walnut shell blasting device to clean
off the carbon buildup. Lighter buildup can be removed with the
use of a fuel additive or a fuel with Techron.
Vacuum/pressure leaks anywhere in all of the above mentioned areas may
cause lean/rich running and hard starting. You may also want to have a
mechanic check that the CIS fuel injection system pressures are correct.
After verifying there are no vacuum/pressure leaks, and the fuel system
pressures are correct, the basic idle mixture should be checked and
adjusted if necessary. This can be done by either measuring the CO% of
the upstream exhaust gas (O2 sensor disconnected and using the exhaust
analyzer connected to the small metal pipe with the blue cap) Adjust the
upstream CO% to be around 1.2% using the Bentley procedure for your
model car. The later 200TQ's use a slightly different procedure.
You can also adjust the idle mixture by measuring the duty cycle of the
CIS frequency valve that is used to tweak the mixture.
This assumes the O2 sensor is connected, working correctly and is
warmed up (O2 heater working ok) . Again, follow the Bentley procedure.
Even though this duty cycle changes back and forth between different
values usually the "average" duty cycle should be adjusted to be around 38%.
This corresponds to a upstream CO% around 1.2%. Getting this adjusted
correctly is very important to ensure good initial cold running and
is required for correct full throttle enrichment under high boost!
The throttle switch which provides idle and full throttle
information to the ECU should be tested for correct operation as this
part typically develops poor internal connections which may
cause strange idle behavior, the idle stabilzer valve can also stick
from oil/crude built up inside. Cleaning with carb cleaner may help.
A defective throttle switch can also prevent the correct operation
of the Waste Gate (WG) solenoid system that the ECU uses to
adjust the turbo boost. The wastegate control hoses should be checked
for cracks! The large main hose coming from the intake manifold and
going to the lower chamber of the WG delivers pressure to open
the WG. Leaks in this hose can cause overboost conditions! The small
hoses connected to the WG solenoid and WG should be checked. The
internal WG diaphram can also develop leaks and may prevent correct
operation of the WG. The air temp sensor connections could be
intermittent as well. This sensor is located on the intercooler exit.
The self-diagnostic system test should be run to make sure that
there are no other faults in the engine control system. You need
to do a 3rd gear full throttle run to exercise this diagnostic
system correctly. The car should not be shut off after doing this
full throttle run on the 86-88 1/2 5000TQ/early 200TQ's as
the fault memory will be erased. The later 200TQ's with dual
knock sensors (MAC14 ECU) have a non-volatile memory
for the fault codes that can be read later even if the car has been
turned off. Check the Bentley procedure for more info.
The Audi I5 turbo engines are very robust motors but
running Higher Boost levels obviously places additional stresses on
the internal engine components. You may want to do a
compression test to locate any weak cylinders before raising the
boost. Running higher boost can also affect the exhaust manifold/system.
Cracked exhaust manifolds and or broken exhaust studs can result even
running stock levels of boost. The catalytic convertor and muffler
system can get plugged or restricted over the life of a car which may
cause poor running with low power. Catalytic Convertor meltdown
can occur with overly rich mixtures at sustained full throttle running
when immediately followed by normal lean running or idling.
If you ever need a reminder to let your engine run
after a high boost run, just open up your hood at night and
see the red hot exhaust manifold and turbo! Even with the
water cooled turbo you should let the car idle for several minutes.
It may take 10-15 minutes of normal low boost driving before
the exhaust manifold/turbo cool down. It is a good idea to avoid
high boost initially after starting a cold engine until the oil temp
gets up to 60C (this is recommended in the factory operators manual)
Driving with more boost/horsepower also places more stress on
the transmission, clutch, suspension system and tires. People
running cars with automatic transmissions may want to limit
how much your boost level increases as these transmissions
are not very robust. FWD cars may become dangerous to drive
under high boost levels as they tend to torque steer and this may
result in the loss of control and an accident.
The two hydraulic engine mounts and the rear transmission mounts
should be checked, the exhaust side (passenger side) engine mount is
subjected to a lot of heat (check that the hose is installed correctly
that provides fresh air to this mount). A defective hydraulic engine
mount on this side tends to place more stress on the exhaust
manifold/system. Of course the tires, CV joints, wheel bearings,
shocks, subframe bushings and other suspension bushings/parts
subject to wear and tear should be replaced where necessary.
Others may have want to add additional comments or
improvements to this information.
Happy Holidays to everyone
Hoping your Audi finds some snow to play in
89 200TQ with
MC engine (2 knock sensors),
Home Brewed EPROM with Overboost to 2.0 bar
STEADIRIC suspension kit, hoping my kit
instructions and refund check are in the mail......