fuel troubles
 

a few weeks ago I accidentaly put plus 89 octane in my 95 svx instead of 93 octane premium. I was at mobil who puts their premium in the center of the three pumps where every other gas station puts their plus. and stupidly i wasn't looking at the octane rating and put in the gas on the end, where the premium usually is. Ever since then my car has trouble starting up cold first thing in the morning (which has been getting better after about 4 or 5 tanks of premium), and makes a weird rumbing sound for the first 5 minutes, and if i press the accelerator the engine stalls. Besides that the car runs fine. The other problem is that the check engine light has been on ever since and does not go off. Is the problem that the oxygen sensors need replacing? At the motorsport warehouse site it said in the product description that bad oxygen sensors would cause the check engine light to go on, and that they would need to be replaced every 80k miles, which my car just hit.

Incorrect octane will neither cause the check engine light to come on nor cause it to start hard. If anything lower octane would start easier. I'm not sure (without looking it up) but I think that the '95 may be OBDII diagnostics and currently there are a possible 1,999 possible codes available (even though no manufacturer uses all the options.) My point is there is many things that can turn the light on. Do a search here for how to check for problem codes or stop at an Autozone or similar parts store - many do diagnostic checks for free.

Methinks '95 was a year split between OBDI and OBDII. Most here have been OBDI. If you have a port instead of a coin holder on the dash it's OBDII. Anywho, What Beav said.... :D

Wouldn't the lower octane potentially cause knocking, which in turn would cause the check engine light?

VK

svxcalibur,

My son did a similar thing to his '94 - used low octane gas - and it caused the same systems to describe. What worked for us was, we ran it till it was almost out of gas, then refilled with premium and STP gas treatment…. We did this twice. The car started and ran much better. Then we disconnected the battery for about 24 hours (to clear the codes - see archived posts)…. And the check light hasn’t come back on since…

Good luck..

who's that knocking?
 

The ECU should detect the lower octane knock via the knock sensors and adjust the ignition advance accordingly. No fault should be generated unless some sensor is out of spec. ;)

Naw, if the knock sensors were bad the computer would have no way of knowing it was knocking. If they're o.k. they'll send a signal to the computer until it retards the timing far enough to make the knocking quit. Usually most computers retard the timing in three degree increments until it quits. Generally more noticeable in mpg than performance.

techno babble
 

sorry, but seeing as I am new to this car perhaps you could explain what OBDI and OBDII are? I guess I must have OBDI because I have a coin tray in my dashboard. What I forgot to mention is that I put some 104 octane boost in after I realized what I did. This had helped before on my other SVX (I realize I just said I'm new to this so I'll explain). I bought my first svx a few months ago, it was a dark red, maroon '92. 42 hours after I bought it while taking a arbitrary drive An old couple just out of the hospital cut in front of me. I never saw them coming and had no reaction time and therefore didn't break. I broadsided them at 50mph and totalled my car. I loved it so much that I had to buy another one (luckily the insurance agency paid me double what I bought the car for). Anyway, being a kid with a low paying fast food job I tried on the first and only time I filled that first svx to use 87 octane to save money (I had not yet learned of the large compression ratio), the next day on the short 10 minute drive to school the car stalled 3 times. I put a bottle of 104 octane boost which fixed the car. Anyway, that was my experience.

If you fill the car with the proper fuel for the next couple tanks it will adjust itself for more optimum timing. Or you can leave the battery disconnected overnight and the computer will be forced to re-learn all its parameters. No dangers, just sometimes a pain while it sorts itself back out over a few days.

I still find it hard to believe that the fuel grade had much, if anything, to do with it stalling.

I just discovered that it needed 93 octane too. I put in 89, 'cause I wasn't sure. My SVX came with no manual and it is conveniently not listed in the fuel door. My light came on three times on the highway.... I hope I didn't hurt it. I apologized many times. I have some octane booster I used to use in my buick that is going in the SVX in the morning. It was the richdale gas station too! So I seriously doubt that it was 89, probably why it acted up so quickly. In the back of my head I knew this needed 93, but I do everything the hard way.

Beav and Boone are correct
 

Im with beav and boone. The processor will adjust for lower octane without generating a code. I really can't see that octane would cause a code.