200 miles to a tank

[beauregaardhooligan]

Sorry, McBrat. I just love a good argu, uh, discussion.

Did you get the injector tightened?

I don't have a turbo, but I thought they only boost when you are accelerating. Shouldn't the mpgs be about the same as a n/a motor if you keep your foot out of it? (Yeah, right, like that's gonna happen!)

How hard is the turbo working at a steady 75mph?

I was under the assumption that a turbo would improve economy under normal driving conditions.

What octane do you run?

Any pinging under heavy load?

Do you have the Accel coil?

[RenaissanceMan]

despite how long this has been argued for, I think one point has been overlooked.

 

Carbureted, vs computer carb, vs fuel injection.

 

As stated, octane is a cumbustion supressant... aka - it combusts at a hotter temperature.

 

Now, back in the day, all that controlled the fuel was the carburetor itself. Whatever came out the exhaust had no affect on what the carb put in. So, theoretically, a slower burning fuel would leave deposits in the engine and lack some performace from an incomplete burn.

 

 

*HOWEVER:*

 

Technology has introduced the "oxygen sensor" which my 84 wagon is equiped with of course. The computer is now able to read what the exhaust output is.

-Lets throw some scenarios out there: Using a higher octane, the computer will notice the exhaust is rich, from unburnt fuel, and will lean out the fuel mixture, by adding a couple controlled air leaks to the intake manifold, The leaner mixture increases the combustion chamber mixture, therefore allowing a complete burn. The computer "programs" itself to memory and remembers the ideal mixture for the norm of the car.

 

Using a lower octane, and running a lean mixture, the computer will sense the exhaust contains too much oxygen because it was never all used, and close up the air leaks, run richer, cool down the combustion

 

*FURTHER*

 

so now everything is fuel injected, along with increased performance and economy, the "knock sensor" was added. Working in conjunction with the oxy sensor, and temperature sensors, air flow sensors, etc etc... THe knock sensor tells the computer when the engine is pre-igniting from being too lean. Overall it can get extremely accurate in getting the right mixture.

 

 

Anyway, point being, if your engine cannot automatically adjust the mixture, then yes there will be problems with performance, and increased deposits, but it STILL WILL BE COOLER. With modern engines (computer carb and up) the higher octane can be used

 

In my 84 EA81 manual, it specifically states "engine designed for use of 90 octane or above" I suspect this could be because of at the time the engine was produced, this was considered to be high compression -8.5:1 is it? Designing the engine for torque meant keeping the advance low, only 8 degrees, at this low of an advace the pre-igniting was a problem...

*IF* you advance your timing, you will lose some low end, but can get away with a lower octane, in some cases. However advancing will also increase engine temperature, so there are limitations and exceptions to this. If you look at the timing for a lot of more recent engines, its much further advanced, allowing a higher compression, with less octane, because cooling is more efficient.

 

Someone quoted that their explorer should only run on a maximum of 87 octane... well if the pulse width modulation for the injectors can only go so low, then trying to give the engine less fuel wont happen, and yes your engine will get dirty because of it.

 

My honda VT1100 looses all kinds of lower end on a lower octane, and on a 2 cylinder torque monster like that, trust me, you can feel the difference. In the summer I could probably get away with lower octane, but in the winter, its cold enough here (yeah yeah california I know), that to keep the engine running decently I need to use the higher octane just to keep the engine warmed up to a decent operating temperature, but now I am getting off topic. I always use 91 in my subaru, and anything less and it runs like *#&@!

[GeneralDisorder]

We are discussing carbureted EA81's here - the feedback carb is a rare exception to this conversation - and computer controlled FI applies to none of these engines (with the exception of the EA81T - which is a completely different beast).

 

Also - Octane is NOT a combustion suppressent - it is a measure of the resistance to detonation - or how hard it is to get it to burn. Take diesel for instance - VERY high octane rating - but much lower BTU's per gallon than gasoline. No - lower octane fuels burn hotter and more completely due to their higher BTU rating.

 

And running water into the engine to clean it is quite normal - many shops use this technique - it won't hydrolock if you keep the R's up. My shop teacher reccomended this approach to our class after a demostration of cleaning parts with a steam cleaner....

 

Apparently anything that doesn't aggree with what YOU believe must be wrong - your very stubborn, and I see that I will not convince you with educated answers. Your rebuttles are mis-informed, and badly worded. If this were a debate, and there were a panel of judges, I would surely have won already. I'm am sorry - but I cannot continue this discussion further.

 

GD

[Qman]

Originally posted by GeneralDisorder

We are discussing carbureted EA81's here -

 

After reading the entire post again, I see that we have gone off track. Yes, octane was brought up. And, yes, different opinions have definitely been discussed. But the point that has been forgotten is this...

Originally posted by Stupidru

My ea81t is only getting 200 miles to a tank, I've tried about 5 different types of fuel injection cleaner to no avail.

 

We should be trying to answer the question of the poster instead of arguing octane ratings and perceptions of such. This has been debated(low vs. high octane) since inception.

 

It is fine to discuss/debate and even argue about it in the appropriate forum(Off-topic).

 

The EA81T is not carburated. It is a computer controlled engine management sytem. Two of them actually. I think the problem with mileage is not relative to octane as much as it is to connections of components, electrical part failure. It could be as simple as having the injectors professionally cleaned. Changing the O2 sensor or resealing the motor. Any number of things can attribute to poor mileage.

 

Good luck

[GeneralDisorder]

Ah - absolutely true. Although the original post is extremely old - somehow it was brought back frorm the dead - and then strangely enough it got WAY off topic.... my fault really. Sorry about that.

 

GD