If your 4-cylinder 1990 Toyota Camry DX is not getting good gas millege is it smart to switch to a higher octane gas and when is the best time to do this?

Answer 1

dont waste your moneyHigher octane is not going to help, it's only for high compression engines to prevent pre-ignition (knock). You should try a tune up. New fuel filter, air filter spark plugs and wires, pcv valve and a bottle of good fuel injector cleaner that you add first to gas tank then fill up with gas (Techron is a good option for this). The only situation where higher octane would help with an engine not requiring it is if there is heavy carbon buildup in the cylinders causing pre-ignition and even than it's a temporary fix until they can be properly cleaned.

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I agree completely.

However, even if you don't have a check engine light you should test your Oxygen(O2) sensors if you are handy like that.

They will start to fail without the computer knowing it by sending erroneous voltages back to the computer. They will be wrong but still within range so the computer has no idea it is getting bad information.

If you do replace the oxygen sensors you MUST use the proper Denso sensors. If you use Bosch or some other brand you will regret it. They either fail immediately or give you the same condition you had before by giving the computer inaccurate information.