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Water
Water can severely damage automotive electronics. Immediate functional failure may occur or an
electronic unit may fail in the future. Water has a more detrimental effect on the active components
(integrated circuits - I.C.) versus the passive components (resistors and capacitors). The packaging
used for the I.C. wasn't designed to be submerged in water, and only for moisture resistance with
ceramic type packages and not plastic which is the most common type for non-military applications.
Vehicles such as the 911/964/993/996 with electronics mounted on the body pan are prone to have
water damaged electronics. This is especially true for Cabriolet and Targa vehicles which may have
leaky tops. Also, some late model three series BMWs may incur water damaged electronics because
of water drainage problems for the control unit compartment in the engine firewall.
The water must be removed as soon as possible or the electronic unit generally cannot be repaired
with good long term reliability. The vehicle must not be started before the water is removed and
the unit is repaired. If this procedure is not followed, additional damage to
a unit may occur. As a
preventive measure, the source of water must be diverted and the leaks sealed.
Overvoltage
Overvoltaging of automotive electronics can result from an overcharging alternator or a high
capacity battery charger. In most cases the damage is catastrophic to the units. Overcharging
alternators are difficult to avoid. Once an overcharging condition is discovered, e.g. buzzers
going off, bright headlights or eradicate tachs, the alternator or the regulator should be replaced.
When charging a dead battery, the battery should always be disconnected prior to connecting the
charger. The small trickle chargers of less than an amp capacity generally are not a problem.
The most damaging situation occurs when trying to start a vehicle with a dead battery by means
of the large capacity chargers which have vehicle starting capabilities. Always pre-charge the dead
battery or use a jumper battery to start a vehicle with a dead battery. Once the battery is fully
charged, the maximum "key out" current draw should be less than 70ma (.07amps) to have a good
battery after two weeks of non-use.
Also, when checking an alternator output for voltage and current, always begin by testing at the
alternator output terminal and not at the battery because of possible voltage drops in the wiring
from the alternator to the battery. Furthermore, most Bosch alternators require that the alternator
warning light function properly, i.e. light up with the key in the "run" position and be "off" when the
engine starts. If the light stays "on" after the engine starts, then there's a fault in the alternator or the
wiring from the alternator to the battery.
Reverse Voltage
Reverse voltaging of electronic units will result in a catastrophic failure of the units. This usually
occurs when jump starting a dead battery vehicle or replacing the vehicle's battery. Initially, the
vehicle's alternator will be damaged and if the ignition switch is "on" all the vehicle's electronics will
be subjected to the reverse voltage. Some vehicles protect key electronic control units with reverse
voltage prevention relays, but this feature can't be relied on to protect control units from damage.
Only by carefully replacing the vehicle's battery or by properly attaching the jumper battery can
reverse voltage problems be avoided. Always connect the negative lead of the jumper battery to
the engine or the vehicle's chassis and the plus lead of the jumper to the plus lead of the battery.
This reverse voltage problem can severely damage automotive electronics beyond repair. Wiring
harnesses can be burned requiring replacement, which in many cases is very difficult. Also, fires can
be started when this problem occurs.
Vibration
Vibrations to automotive electronics can be very problematic leading to intermittent control unit
functionality or eventual total failure. A major problem leading to vibration failures results from how
the control unit's circuit boards set relative to the vibration motion. If the circuit boards are positioned
in a plane which is perpendicular to the vibration motion, the boards are flexed more than if they are
mounted in a plane parallel to the vibration motion. This flexing causes the solder connections to crack
and "open", e.g. resulting in an intermittent ECU or relay unit. ECUs which use a cantilever mounting
system are more problematic than systems which eliminate flexing of the ECUs.
This problem occurs in most Porsches and in pre-1990's BMW's, since the control units are mounted
horizontally on the body pans or above the glove compartments. Vibration is not as problematic with
later electronics, as most automotive electronics use surface mount technology (SMT) parts. These
types of parts attach to the circuit boards in a much more reliable method. Large types of components
such as power resistors or relays still present a vibration problem. The mounting method for control
units which include these components can be a source of intermittent problems. Another example of
this problem is the Bosch CDI unit used on the early Porsche 911s which was mounted on a bracket
that transmitted vibrations to the unit resulting in intermittent running problems.
Additionally, the larger power control relays, e.g. a 3.2 Porsche 911 DME relay, are affected by the
mounting method (cantilever) and the resulting vibrations which can cause intermittent starting/running
problems. Similar failures occur with early Porsche cab top control units because of the large relays
used and the cantilever mounting used for this ECU also. Relay failures also occur because of contact
oxidation which results from the current level switched over time.
Performance Chips
Performance enhancements for digital fuel injection systems involve the replacement of an EPROM
chip or the reprogramming (flashing) of an EEPROM chip within the fuel injection unit. The modified
chip data must be determined thru the use of a dynamometer to maximize the torque over the full
RPM range. Just modifying the chip data by using a computer to re-map the chip will usually result in
torque peaks and losses, and thereby usually provides little to no overall performance enhancement.
Generally, most fuel injection map changes without modified intake air flow or exhausts yield very
little in a performance increase. This becomes even less effective when an oxygen sensor is being
utilized. Some performance chips, though, may disable the O2 sensor input to achieve more throttle
response. The only real performance increase results from changes to the ignition maps by advancing
the timing. This usually becomes less effective with fuel injection systems that utilize knock sensors.
An analysis of a number of performance chips' fuel and ignition maps has provided insights into
what actually is modified. All the performance chips analyzed had basically the identical fuel maps
as the stock/original factory chips. The significant differences were the "pushed" ignition maps. Some
performance chips had ignition advance values exceeding 50 degrees, where the maximum BTDC
value for a 911 Porsche should not exceed 40 degrees for octane ratings and fuels available today.
Pinging or detonation can occur for non-knock sensor systems when ignition maps are advanced
beyond a few degrees, or when knock sensor ignition systems are "pushed" beyond the knock control
to achieve the desired performance. This may result in some possible engine damage. Furthermore,
changes to the fuel injection system may result in increased levels of emissions, e.g. CO & NOx.
These new levels can cause catalytic converter problems or cause emissions test failures. Additionally,
systems with OBDII diagnostics may incur additional problems with emissions testing.
When considering the replacement of a stock chip with a performance chip, dynamometer test results
should be provided by the chip supplier of the "before and after" torque curves. Also, the "before and
after" emissions levels should be provided, e.g. the CO and NOx levels. Without this data, evaluating
and using a performance chip becomes much more of a gamble. Additionally, the replacement of stock
fuel injection maps, e.g. a performance chip change, will usually require an increase in the octane level
to avoid pinging. The pinging which occurs may be inaudible, thus causing unknown damage to the
engine which makes using a performance chip even more of a gamble.
Emissions Tests
Emissions failures result from excessive levels of CO (carbon monoxide), HC (hydrocarbons), or,
NOx (oxides of nitrogen). Some emission regulatory facilities just require static tests (an unloaded
engine) and others require a dynamic emissions test (a loaded engine via a basic dyno). Late model
vehicles ('96 and later - OBDII) require an additional initial test check of the OBDII readiness
states. A failure of the readiness states being complete results in the emissions test being aborted.
The readiness states consist of non-continuous (at startup) and continuous (while driving) tests.
Completion of the tests may require additional driving of the vehicle or a mechanical correction to
the emissions system on the engine. Some non-continuous readiness states can be run using vehicle
specific scanners.
A high CO level can result from a bad fuel pressure regulator, a bad air flow meter or air mass sensor,
a performance chip, a bad temperature sensor, or a bad O2 (oxygen) sensor. A HC level failure can
result from a bad fuel injector, a weak cylinder, bad spark plugs or ignition wires, an intake air leak
or a bad O2 sensor. A NOx level failure can result from a too advanced ignition timing (installed
performance chip), a lean fuel mixture, or a weak catalytic converter. The typical values for each are;
CO < 1%, HC < 100 ppm, and NOx < 500 ppm. The level of CO2 (carbon dioxide) which results
from the catalytic converter reaction is a measure of the effectiveness of the catalytic converter.
Typical values of CO2 are 13 to 15 percent.
Lastly, a bad fuel injection unit or ignition control unit may be the cause of any emissions test failure.
The above mentioned possibilities, though, should always be checked before assuming bad control
units or performing other costly repairs.
Diagnostics
Diagnostic equipment, e.g. OBDII scanners, data are essential for diagnosing late model vehicle faults,
but can result in costly replacements of non-faulty vehicle components, e.g. MAF sensors, ECUs,
when not supplemented by further diagnostics. Some situations may occur where diagnostics do not
indicate any faults but yet a driver displayed fault may exist, e.g. "Brakes: Do Not Drive". Here and
in most more complex problems, a full understanding of the overall vehicle systems is necessary.
Thus in most situations, further diagnostics are always required besides just reading the DTC and
the replacement of its indicated faulty component.
As an example, the DTC may indicate a faulty MAF sensor because the TRIM value has reached its
limit, but the actual problem may be the fuel pressure regulator. In another situation, the DTC may
indicate a shorted actuator to ground, but the output driver of the ECU providing the DTC may be
the actual problem. Also, assuming that an ECU is faulty because of no CAN communications,
where the CAN gateway may be faulty or another ECU may "hang" the CAN bus, can be misleading.
Thus, the DTC data should never be considered as an absolute in determining the source of the
actual problem. The DTC data should always be considered as a troubleshooting starting point for
further diagnostics to eliminate other possibilities.
DTC data can be supplemented by reading the actual values, i.e. live data, if the diagnostic equipment
has that functionality. A conclusive determination of the faulty component may require the use of a
multimeter and/or an oscilloscope. Comparative data from a known good component can be used.
The "acid test", as always, is the replacement of the potentially bad component with a known good
spare component and the subsequent elimination of the DTC fault. This may not always be possible,
though, e.g. a costly/unavailable component and/or special coding of an ECU. But only when additional
supportive data are determined, should the component be considered as the actual problem source
and then be replaced.
Troubleshooting
When troubleshooting automotive electronics, extreme care must used or the electronics may be
damaged. The use of non-electronic test lights (incandescent bulb types) are to be avoided. Resistance
measurements should always be checked with all power sources removed. Supplying a test voltage
to a control unit input should be done thru an appropriate resistor or a test light to prevent excessive
and damaging currents.
Electronic control units can damaged by improper engine ground connections. Also, all ground
connections for a control unit must be present or an alternate ground path may damage another
control unit. When testing motors, relays, or injectors, control unit output connections should never be
connected to +12 or ground without disconnecting the control unit. The CD ignition's output should
never be tested with any type of test light, only with a scope, nor be subjected to +12 or ground.
Also, fuel injector signals should be tested with a LED type of test light or a scope.
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