The previous owner jack-ass told me after I bought the car that he used 89 octane and thought it ran fine. Has using 89 octane been a disaster for my motor? What should I expect? It has 36k miles on it now and seems to be running fine. And if anyone is wondering, I'm using 91 now.

 

It might be OK. The car has a knock sensor, so the computer retards timing to reduce power. The possible issue is that the engine has to ping/knock in the first place before the computer adjusts. If the previous owner did a lot of hard driving, hot weather driving, then there might be a lot of times the engine knocked. Once in a while wouldn't be an issue, but for 30k +, I don't know.

 

o man, that doesn't sound good.

 

Well, you bought a used car. You got what you got. You say it seems to run fine and it most likely is fine. Just drive it. If there was damage (doubt it, but who knows) it would take the form of excessive wear and there would really be nothing to do at this point. So, just drive it and enjoy it and put the recommended fuel in it.

 

.... The ECU should retard timing to prevent detonation. It's not mis-firing is it? I think that lower grade fuel will just increase wear, not cause traumatic damage. But then again, I am not a mechanic. Might take a few thousand miles off the total life of the engine, though.

John

 

^^the problem is, before the ECU will actually retard timing, it must first detect detonation. ANY detonation is bad. the chances of causing damage are slim, but possible. however, since the ECU will continue to try to bring the timing back to normal, it will do so until it detects detonation again.

so using lower octane gas WILL cause detonation. then the ECU will retard timing. but then it will advance it again to try to get back to normal. and then you'll get detonation again. and the cycle continues.

the correct statment would be "the ECU will retard timing to prevent CONSTANT detonation".

while driving at low rpm with little gas and doing all freeway driving might be ok, chances are this is not what the previous owner did. the only way to be sure if there was excess wear and tear (IMO there probably is), would be to open up the engine and take a look at the valves and pistons. i'm willing to bet they'll be some of them that look "burnt". i've seen it before on S2000's that did not use premium.

as to what kind of negative effects this will have, only time will tell. IMO, i'd try to get my money back and give the car back, or try to get money from him. he was dishonest with you before selling you the car, and in fact, was quite abusive to the car considering his blatent disregard for what the manual specifies.

 

Damn, Matt. I was just trying to make the guy feel a little better. You won't get any argument from me that running low octane for extended periods is bad.

BTW, does anyone know of a way to tell when timing retardation is taking place, or in other words, when the knock sensor is detecting predetonation?

 

This is exactly why I would never buy a used performance car

 

WOW... thanks for ur honesty. unfortunately, giving the car back is not an option since the sales contract has already been signed and the title transfered. But the good news is, the guy bought an extended warranty that covers the motor till next year or 70k. what should i tell honda in terms of the reason for the diagnosis? should i tell them its running funny or sounds funny etc...? will they cover the excessive wear or any damage that was caused?

 

I know a few guys with new preludes,(00-01) they have had alot of trouble when they use lower octane gases.

Edit: fixed my poor grammar