I always go to sunoco and put 93 octane in the car. Then a friend told me that I am wasting my money, that cars are made to run on 87 octane (besides specialty cars of course) so I was thinking about downgrading to the 87 octane and then wondered if the car would run at the ecm settings for the higher octane rating until the ecm cycled again and read the difference in the grade. If in fact thats what it does. oh its an 88 duke 5sp.
You'd need to readjust the timing a tad. In the old days, my 66 Pontiac required premium fuel and I put in regular. I had to reset the timing to stop the "pinging" until I used up that gas and went back to premium. This was when hi-test was maybe $0.40/gallon max and regular was $0.30/gallon. The ECM in a Fiero is rather a simple computer when compared to todays cars computers.
For the ECM to adapt to different grades of gasoline, the engine would need a knock sensor. Neither the 2.8 nor the 2.5 have one. On more modern engines the ECM advances the ignition timing until it detects a knock, then readjusts accordingly.
Up until the introduction of flex fuel vehicles, the ECM's compensated for type of fuel the exact opposite as most people think. They never took advantage of running higher octane, the engines were built and tuned for a specific octane. There were several engines designed to run with 91+ octane to maximize performance, but the ECM doesn't compensate for the higher octane in these engines, it is the default design parameter.
When you run a lower octane than specified it will likely knock. The ECM will see this (if the engine has knock sensors) and pull timing. So the only action a non-flex fuel ecm takes in regards to octane is to pull timing when you run lower than needed octane (and the car has knock sensors). The ECM does nothing for running higher octane than needed.
The flex fuel engines needed to know the % alcohol the fuel in the tank, so they have a fuel sensor that measures it directly and then adjusts the fueling and timing when the fuel is anywhere between E15 to E85. This isn't really an adjustment for octane, its an adjustment for alcohol content. However, octane increases with alcohol content do it indirectly does compensate for higher octane.
On the 2.8's you can manually adjust to take advantage of the higher octane fuel by increasing the timing (increase base timing - or add timing in the tune), but the ECM doesn't make any adjustments on its own. But w/o a knock sensor to protect the engine, doing so is risky as best.
With your car being an 88 2.5, you can't bump the timing because it is DIS and last I knew no one offered any tuning software for it.
I have an 88 2.5 and run the cheapest fuel I can find through it.
For stock (or near stock) Fiero engines used as daily drivers, there is zero benefit of running higher octane fuel.
Originally posted by yellow peril: I always go to sunoco and put 93 octane in the car. Then a friend told me that I am wasting my money, that cars are made to run on 87 octane....
Your friend may very well be correct about most cars built currently, but what octane level, specifically, does the GM owner's manual recommend for your 5-speed, Duke-powered, 1988 Fiero, which now is 26 years old?
Correct. The only benefit is a better additive package that may help the engine run cleaner. No advantage to the octane and no increased power. If you're running a quality brand fuel, you should be ok.
Your friend may very well be correct about most cars built currently, but what octane level, specifically, does the GM owner's manual recommend for your 5-speed, Duke-powered, 1988 Fiero, which now is 26 years old?
I'm pretty certain the original design specification for the Fiero engine was 85 octane.
Originally posted by jscott1: This is 99% true, however some premium (i.e. high octane) fuels contain more extensive additive packages which might provide some benefit.
this is covered in my cave for years... Fuel & Knock
1. All gas in the US and Canada should meet rules for cleaner additives.
2. Texaco System3 was first that made cleaner in all grades. Now "Top Tier" fuels have same cleaners in all grades.
If you want "better" cleaners then use 87 octane from Top Tier Retailers
I had a new ECM programmed for my 1996 Sonoma with 4.3 because I was having problems with the old one. Thats the very beginning of OBD2. The place that programmed it asked what octane I'd like it optimized for and if id like it set to consider 10% ethanol. They also set it up to optimize for my cold air intake and larger diameter exhaust pipe. I was skeptical about the actuality of programming it for the gas. But the end result was it does feel like it has better power. (seat of the pants) I'm not saying they did all this, but they said they did.
I dont think OBD1 can.
[This message has been edited by 2.5 (edited 09-29-2014).]
Now "Top Tier" fuels have same cleaners in all grades.
This is not entirely accurate. It's more accurate to state that all top tier gasolines contain the same MINIMUM level of cleaners in all grades. The premium grades still can contain more extensive additive packages. This is how brands attempt to differentiate themselves from their competitors.
[This message has been edited by jscott1 (edited 10-02-2014).]
Originally posted by 2.5: I had a new ECM programmed for my 1996 Sonoma with 4.3 because I was having problems with the old one. Thats the very beginning of OBD2. The place that programmed it asked what octane I'd like it optimized for and if id like it set to consider 10% ethanol. They also set it up to optimize for my cold air intake and larger diameter exhaust pipe. I was skeptical about the actuality of programming it for the gas. But the end result was it does feel like it has better power. (seat of the pants) I'm not saying they did all this, but they said they did.
I dont think OBD1 can.
All they did was adjust the timing, which you can do with OBD1 as well. Only more recent vehicles with flex-fuel capability actually have a sensor for the fuel type. Vehicles without flex-fuel capability can have their programming altered for better use of a specific fuel type, but it is not an automatic adjustment. In the Fiero, you can just adjust the base timing by jumping the ALDL pins and then turning the distributor.
