Yes I know 87 octane is not good at WOT, but there is no knock at constant 2000rpms for 16 miles. But I do 90% highway driving to work now. I just moved to California and a job ( = low fund$) and with premium knocking on $5 a gallon and not racing the thing, I know it doesn't hurt the car.
However, a yahoo made me have to downshift and pass and around 5500 there was a misfire/stumble. I did it again, yes I know 87 octane is in there, and it didn't happen. Drove the rest of the way home, 8 miles. I wanted to see if it would do it again, and it did.

Will 87 octane do that? Other than that, car is tip top. New coil and coil wire, plugs and wires.

I just finished a horrible tank of gas 1 week ago, 91 octane got me 14.4mpg and i had about 2 gallons of that crap still in my tank. Filled up again but with 87 octane and got 18.7mpg. Now this is with 70-80% highway, not that great. A month ago when I moved here, it was getting almost 27mpg on 87 octane from Phoenix to San Diego.

Yes I know there are variables, but this is more of a vent and to ask, will 87 octane cause a misfire so high in the rpm range.

 

Might not be a misfire, might be the PCM pulling timing because of the low octane fuel.

You won't hear knock - the knock sensor picks it up and the PCM responds faster than you can hear it. You're just losing power most of the time, and getting reduced fuel mileage because of the retarded timing.

 

I was thinking it could be pulled timing, but it feels more like when the coil went out, but just not as broad a range of misfires.

Like I said, I know 87 isn't good and I stay out of the throttle 99% of the time. But the gas here is crap. Maybe they are letting the maximum amount of condensation stay in the tanks to maximize profits. Ive been reading up on that too.

Oh well. I'll be back in AZ in a month and my brother and I will do some scans.

 

If you have audible knock under any conditions - premium grade or regular - you have a problem. The knock sensor should prevent it. Get it checked.

 

theres a reason our cars say "premium fuel only"

 

Except, of course, in the owners manual where it states you can use middle grade or regular grade unleaded and the only issue will be the car will be down on power. It's on page 185 in the 94 manual. Anyway, it shouldn't knock, even on regular and the PCM will pull timing to correct. As injuneer stated, if he has audible detonation he has a problem....

 

The guy has a '94 and who knows if his 17 year old knock sensor is even working.

 

That would be one of the possible problems, all right. Along with carbon build up and a few other things. Point is, 87 octane won't cause it to audibly knock....

 

He might just have ignition breaking up at high rpms.

But if it didn't retard the spark enough it could be audible knock, and maybe the gas is bad as well. These cars have pretty agressive timing and high compression. He might also have stock head temps and carbon buildup, and/or too hot of a plug. Combine that with peak torque. Cars used to rattle all the time before they had the sophisticated knock retard systems they have today.

 

No, it doesn't say that, as Bruce has already pointed out.

If its an electrical failure, he would have a code, and the PCM would be pulling timing. If its some sort of plugged up sensor, I guess it might not work

Was the Caprice iron head LT1, with its lower compression ratio meant to run regular? I could be wrong - I never read the Owner's Manual.

 

What happens to the sensors when they get old is that the piezo crystal can wear out just like on your gas barbecue. Not sure if rust and grunge from the cooling system would have any effect on it.

 

Its not audible at all. I just feel it pull back or hesitate. I do think its just pulling timing at that rpm is all. All the sensors are functioning as they should, we scanned a bunch of times before I left AZ. The car is tip top in that regard.

Z28Roxy, yes I absolutely LOVE the hills here in SoCal and the pot holes, and the concrete laid over the broken asphalt. LOVE IT LOVE IT LOVE IT.