Runs poorly on 93 octane

[4xdog]

...throw money away...

We're in complete agreement there, schnutzy. Higher octane than needed to prevent detonation is a waste.

But that doesn't explain how a car will run poorer on higher octane. That goes against all my experience and everthing I've been taught since Doc Schraeder in my first automotive class at university almost 35 years ago.

[schnutzy]

We're in complete agreement there, schnutzy. Higher octane than needed to prevent detonation is a waste.

But that doesn't explain how a car will run poorer on higher octane.

because it is unable to use all the fuel.
with the higher then recommended octane, your engine is still squirting in the same amount of fuel as it would with the recommended grade, however now, its not burning off all that fuel.

[scrubber3]

because it is unable to use all the fuel.
with the higher then recommended octane, your engine is still squirting in the same amount of fuel as it would with the recommended grade, however now, its not burning off all that fuel.

I can see your point to a degree... But it does not make sense that it ran so poorly. A little hesitation here and there, sure. But it was barely making it up hills. Keeping in mind, that I probably need new spark plugs and that it may enhance the "compression issue" to a point that it runs rough, I even believe that it could be the culprit. But in no way will I believe that with a perfectly running engine 93 octane will make it run worse all by itself.

So theoretically, if I were to tune the timing and injector pulse to compensate for the need for added compression, I could actually save fuel?

[schnutzy]

I can see your point to a degree... But it does not make sense that it ran so poorly. A little hesitation here and there, sure. But it was barely making it up hills. Keeping in mind, that I probably need new spark plugs and that it may enhance the "compression issue" to a point that it runs rough, I even believe that it could be the culprit. But in no way will I believe that with a perfectly running engine 93 octane will make it run worse all by itself.

So theoretically, if I were to tune the timing and injector pulse to compensate for the need for added compression, I could actually save fuel?

yes, bad spark plugs could definitely make it worse. it is kind of like, when one little thing goes wrong, you wont really notice it, but when lots of little things start happening, that all adds up.
but, i can tell you from personal experience, that a perfectly running engine will run noticeably rougher on 93 when 87 is recommended. I experienced it first hand, borrowing my dads 1 year old F150 helping a friend move. I had to throw in a few gallons of premium because at 2 in the morning, the little middle of no where gas station was out of 87. this is actually what caused me to start researching the 87 vs 93 octane thing in the first place, because all those years ago, it made no sense to me that a different octane would cause that.

now as for tuning your montero to run on 93. I am not sure exactly how you would, or why. i run 87 in my LS and I am perfectly happy with the way it runs and have no desire to tune it other wise.

[SOFpirate]

The way I always tricked myself into thinking about gas was this.

The Monty was designed to be driven in 3rd world countries, so 3rd world gas is what I use.

I swear to the Mitsubishi gods themselves, I use this super crappy gas from a very shady gas station that hasn't denied watering down their gas, and it runs like a champ. As soon as I run Shell or Chevron or Tom Thumb or anything of the sorts, she yells at me.

Who knows?

[off-roader]

The way I always tricked myself into thinking about gas was this.

The Monty was designed to be driven in 3rd world countries, so 3rd world gas is what I use.

I swear to the Mitsubishi gods themselves, I use this super crappy gas from a very shady gas station that hasn't denied watering down their gas, and it runs like a champ. As soon as I run Shell or Chevron or Tom Thumb or anything of the sorts, she yells at me.

Who knows?

I would think the mitsu vehicles sold overseas are tuned for the fuels in those countries.

The 3.5l DOHC SR motor for example is set up for premium fuel. It runs better with it and in many cases won't pass smog (here in CA.) without it.

[Quill]

If you put higher octane or fuel with "cleaners" in a dirty fuel system, all the bits of sludge will either clog the fuel filter or start dumping it into your combustion chamber. You normally have a lot of crud in your fuel system that is not bothered until a cleaner hits it and starts removing it. Thus the old saying of better to let sleeping dogs be.

[scrubber3]

replaced the plugs and wires today. Had copper core NGK in it. They we all used up to say the least. Put in platinum NGK with some Denso wires and she runs perfect now. To be honest, I think it was just mere coincidence the whole time.

[off-roader]

Switching to the NGK platinums (or denso's for that matter) was a good call. While it will run on copper plugs most owners I know will run the platinums instead. Also IMHO, all but ngk and denso platinums have been poor replacement plugs for these engines and most especially the 3.5's which require near removal (94/95 SR's) or actual removal of the intake plenum (96 SR) to replace the plugs.

[scrubber3]

Yeah, I had to remove the intake plenum on mine as well. I only use NGK or denso in everything I own including my lawnmower. I chose the platinum due to the durability and the fact that pulling the intake to get to the plugs was quite a chore just to tune it up. I got the NGK platinum plugs, Denso first fit wires, and the gasket replaced and now I am one happy man. Took a couple hours...and well worth the investment. I just cannot believe the last owner put copper core in it. Guess he was low on cash...