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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.

To repeat:
 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

Scott M.
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......