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Background
The recent
fuel contamination problems have been widely covered in the press.
The problems
appear to have been caused by a silicone-based substance contaminating
a tank of unleaded petrol before it reached the pumps.
The exact
source of the contamination has not been fully published, but it has been
suggested that a storage tank had not been completely emptied before being
filled with unleaded petrol. This substance remaining in the tank is thought
to have been an additive for diesel fuels that prevents the fuel foaming
at the pumps. This would not normally be added to petrol.
Why
is this affecting engines?
Whilst petrol
engines appear to be able to 'run' with additive present, the silicone
severely affects one of the key engine sensors – the oxygen (or
lambda) sensor.
This sensor
monitors exhaust gases – feeding the information back to the engine
control unit, which in turn adjusts the fuel and air mixture to keep the
engine running efficiently.
The silicone
in the contaminated fuel forms a coating on these sensors, effectively
preventing them from monitoring the exhaust gases.
As a result,
the information fed to the engine is inaccurate and the engine control
unit cannot correctly control the engine operation.
What
are the symptoms?
- Check
Engine light switching on
- Rough
idling
- Stalling
- Over
or under-fuelling
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How
can you check what is wrong?
When the
Check Engine light is on, the car has stored a fault code that will indicate
where the fault has been found. A handheld
reader or a PC-based
system such as this one can read the fault code.
With a failed
oxygen sensor, the tools will report a fault code such as:
P0133
O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)
P0134 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)
With a PC-based
tool or an advanced
handheld tool, you can also check the voltage readings from the
oxygen sensor. A healthy oxygen sensor will be providing a signal that
fluctuates between about 0.1 and 0.9 Volts, e.g.
Graph
of a healthy, working oxygen sensor
With a contaminated
sensor, the readings will not be fluctuating correctly – either
showing only a very limited range or just remaining at a constant value.
What can be done?
If contamination
is suspected, it is important to ensure that all petrol purchase receipts
are retained. Retailers are starting to offer to settle claims for any
costs incurred.
Even if
the 'damage' has not yet come to light on your car, contamination may
have occurred and the sensor may yet fail earlier than expected (a sensor
will normally operate effectively for 50,000 to 60,000 miles).
It is important
to have the fault codes read from the car to confirm whether oxygen sensor
faults are being reported. This can be done using the tools mentioned
above or by a professional mechanic.
If the oxygen
sensor is faulty, the most common remedy will be replacement
of the oxygen sensor. Replacement sensors are available directly from
the car dealership or from aftermarket
stockists. In some cases, the contaminated sensors can be cleaned
if ultrasonic cleaning equipment is available.
Any remaining
contaminated fuel must also be removed from the car.
Further
information
If you have
any queries on the subject, the testing of sensors or on replacement oxygen
sensors, please contact
us.
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