Check engine light and Chevron gasoline in 96 Avalon

I dont think it is gas. Considering you have 170K miles on it and never had a CEL its just normal wear and tear. Oxygen sensor is what mostly causes the problem and I think just replacing it would solve your problem.

However I do have doubts over quality of gas. My mechenic recommends I use higher quality gas like 91 even though my camry can take 87. I dont kow how much it really affects the peoformance of the car and life of engine. May be someone can shed some light on it. Thanks....

I've read that immediately after a big tanker fills the gas station's underground tanks that sediment is stirred up and can result in a problem similar to what you described. I wonder if that is true, and if it is, how big an effect it is.

If the owners manual calls for 87 and its not pinging run 87. 91 will get you nothing but a higher bill at the pump.

The octane rating of gasoline has nothing to do with "quality." It is simply a measure the gasoline's ability to resist detonation (where the fuel/air mixture burns explosively due to heat and pressure in the combustion chamber, rather than the normal combustion initiated by the spark plug). Engines are designed to run a certain combustion chamber temperatures and pressures and that is what determines the octane rating needed. Buying a higher octane gasoline than the owner's manual calls for provides no benefits and is simply a waste of money.

Merritt

It is probably a coincidence. Rather than take action based on uninformed speculation, you should pull the codes stored in the computer, report them here, and then perhaps someone can make a more informed guess as to what the cause may be.

As several people have posted, if the engine is not pinging on hard acceleration, higher octane gas than recommended by the factory is a waste of money. If the vehicle's ignition will advance enough to take advantage of the higher octane or is a higher compression engine, then the higher octane fuel will have a benefit.

Rather than take your car to a mechanic, I recommend that you take it to an ASE certified technician at least, or if you want to take it to someone who is most familiar with your Toyota, take it to a Toyota Master Diagnostic Technician.

While it is possible that sediment in a gas station's storage tank may be stirred up immediately after being filled, the vehicle's fuel filter should trap it before it gets to the engine. Some gas stations have filters on their pumps.

You should purchase fuel from a gas station that sells a large quantity so that the sediment and water do not have a chance to accumulate. It is not uncommon for some gas stations to get daily deliveries of 8,000 to 10,000 gallons.

Exactly and precisely...while I have very little experience with the technical aspects of automobile engines I have a great deal of technial training and experience with large aircraft piston engines and can vouch for Merritt's statements...I inadvertently ruined a $150,000 aircraft engine in about 5 seconds once because I missed noticing that the 'derichment valve' hadn't returned to normal after takeoff when the 'water injection' was shut off and the engine beat itself to death with heavy detonation.

I was interested and looked up the overhaul strip report on that engine...almost all of the 18 pistons were holed, some of the valves were 'headless' and some of the cylinder heads themselves were split open...gives one a good idea just how destructive heavy detonation can be...

I understand that modern automobile engines are protected with 'fancy pants' systems like 'knock sensors' etc now and these engines in normal circumstances aren't stressed like aircraft and race car engines anyway so detonation isn't nearly the concern now but it certainly isn't something to toss off lightly either.

My theory is that there is no relationship at all. I further theorize you need a new O2 sensor. Just my theory though, your theory may vary.

You are throwing money away if you are in the habit of buying a higher grade fuel than is needed. The ONLY function of high octane is to prevent pre-ignition that comes from heat, compression, and/or advanced timing (or combinations of these maladies), or the normal function of a high performance motor. If your car can run on regular without pinging (pre ignition) typicaly heard under load and climbing hills at speed, then you do not need high octane fuel. Since most Toyota motors are not high compression engines, they do not need high octane gas. Your mechanic is telling you to use fuel that you do not need to use.

Having said that, IF you need to use high octane gas, then you are having problems that the premium fuel is masking, or you have a Toyota model with a high performance engine.

snip

Exactly right in all respects 'except' you're labeling 'ping' as 'preignition' and it isn't...ping is detonation (it occurs 'after' the normal ignition event...

'Preignition' is where the fuel/air charge is ignited 'before' the normal ignition point and is much deadlier...

Just remember that 'preignition' and 'detonation' are two separate, distinct and different occurrences...

My son (a Shell Oil Co engineer) told me a really interesting problem that this local gas station had a few years ago...they'd dip their tanks (with those long wooden dipsticks of course) and find that they'd need XXX gallons of fuel...the tanker'd come and pump 'that' many gallons and stop.

The driver'd dip the tank and find that the dip showed the fuel level about 300 gallons short, yet the tank was full. He'd scratch his head, tell the station owner about it. Station owner would check the dip the next day and would come up with the correct amount

This went on for awhile...nobody could figure what was going on. Shell Oil told my son to 'fix it', took him awhile but eventually he got it.

What was happening was that there was about 300 gallons of water in the bottom of the tank which would be liquid under normal circumstances but when it was being refilled with super cold fuel from the tanker would freeze and hold the dipstick up ~300 gallons from the bottom. (I don't use Shell any more)

And I don't believe the story ;)

mike hunt