The ruling follows a complaint by its rival, Shell, which questioned Texaco's claim that its Clean System 3 petrol was the only fuel to clean not just valves and injectors but also the engine's combustion chamber. Shell maintained there was no industry recognised test to measure petrol performance in the combustion chamber.
Texaco may now have to re-word its advertisement (an example of which can be seen on page 7), jeopardising the impact of its multi-million pound campaign.
However, the BACC has concluded that Texaco's advertisement was ambiguous and needed some amendment. The ruling was confirmed by Shell, which plans to take up the issue with its rival.
But Texaco's marketing gurus were baffled by BACC's censure last Friday. Richard Little, who mastermined the campaign, said: 'We haven't heard anything about this.
'This is very odd as we were able to justify our claims to BACC before the adverts went on air. We will continue to run our campaign unless we hear from BACC.'
The spat between the two companies is the latest of several disputes in the industry over petrol quality. Last year Shell provoked a bitter row after it launched a campaign claiming that cheaper fuel from supermarket forecourts could harm engines because it did not contain detergents and additives.
Initially the Sainsbury supermarket chain threatened to take legal action against the company, claiming it was simply a marketing ploy by oil companies to keep up prices. But the food retailer later made a humiliating U-turn and has since begun to offer petrol with additives to its customers.
Texaco's campaign, which has been running for several weeks, was created by D'Arcy Masius Benton & Bowles, a London-based adertising agency.