Morrisons supermarkets have withdrawn unleaded fuel from sale at 41 outlets following the "faulty fuel" alert.
Two supermarket chains at the centre of the "faulty fuel" alert have moved to stop supplies of suspect petrol.
Tests on petrol taken from the tank of a car affected by allegedly faulty fuel have detected the presence of silicon, trading standards officers have said.
Morrisons has stopped selling unleaded at 41 outlets supplied by the Vopak depot in Essex - at the centre of suspicions over fuel.
Morrisons said it was taking the 'precautionary measure' at locations supplied by the Vopak depot in Essex - at the centre of suspicions over fuel.
Tesco is to empty its unleaded petrol tanks at 150 outlets in the South East, but will refill them with new stocks and continue selling the fuel.
The 237 sites not supplied by Vopak supply will still sell unleaded.
Tesco's own tests found "significant silicon contamination" in its fuel.
Faulty unleaded petrol has been blamed for damaging thousands of cars.
Many drivers said they had filled up their cars at Tesco or Morrisons petrol stations before problems started.
Silicon products are used in diesel as anti-foaming agents, but can cause "serious problems" in petrol engines, a trading standards official said.
Silicon can build up as a deposit on sensors causing them to malfunction Ian Hillier,Trading Standards Institute
Cambridgeshire County Council's trading standards department had the fuel sample tested at a London forensic science laboratory.
Ian Hillier of the Trading Standards Institute said in a statement that silicon could particularly cause problems in modern cars with computerised fuel management systems.
"Silicon can build up as a deposit on sensors causing them to malfunction," he said.
The findings were preliminary and further tests were being carried out, he said.
Insulator
A spokesman for Cambridgeshire Trading Standards said detecting silicon in the fuel could indicate the presence of silicone - a class of chemical compounds containing the element.
Silicone is used in industry as an insulator and for lubrication.
The spokesman said oxygen sensors from faulty cars were being sent to a laboratory for analysis to discover what had made them stop working.
The petrol has been traced to a storage depot in Essex. The fuel industry is testing its own supplies.
It is thought silicone may have found its way into a batch of petrol in transit by ship into the UK or in storage containers.
Automotive expert Professor Malcolm Fox, from the University of Leeds, said low levels of silicone could affect a car's performance.
"When it burns, it will form silicon dioxide and will deposit a very thin sheet on the sensor - the sensor is in the exhaust - and that probably gives a false signal to the engine computer."
