I have a '93 4.0L XLT (Manual)...

I have noticed that I get MUCH better engine performance with 93 octane... the engine runs smoother, quieter, and more powerful.

87 Octane makes the engine run obviously rougher and I don't get so much torque out of it.

I have read somewhere in these forums that I shouldnt be using the higher ocatanes due to carbon build up... so can somebody set me straight on this?

Thanks.

 

Are you sure you're not imagining this? The engine is designed to run on 87 octane, it is tuned for 87 octane.

Running 93 octane will generally lower performance by making the fuel/air mixture harder to burn. Now...when properly tuned via chip or programmer, this allows for more performance. But stock, performance only goes downward with 93 octane.

By causing the spark not to ignite the fuel/air mix at the right point, you get incomplete burning and carbon build up. Carbon build up is already a problem with the 4.0L (hence the suggested 3000 RPM+ run at least once daily), so anything on top of that is no good.

Perhaps you had some pinging before from carbon build up and running the higher octane limited the pinging. I'd suggest running the engine pretty good towards the end of this tank, frequently reving it up above 3K to blow the carbon out, then going back to 87 octane, perhaps with a bottle of injector cleaner.

Hope it helps.

 

Injector cleaneer goes in my tank about once a month or so. I've had the truck for about 6 years, and have put over 150k miles on it in that time. Its @ 197k right now.

I have never done any mods to the truck.

93 octane has always made it run better. kinda weird now that you explained all that too me. No imagination, it runs better and idles smoother with the 93. The tach tends to float around a bit when idleing on 87, and doesnt sound near as smooth. I get more "giddy-up" with the 93 as well.

Strange...

 

Odd indeed...almost sounds as if you have a chip installed.

Either way, that is the octane debate to the very best of my knowledge, I know there are other minor things but that covers most of the big things 'bout it. Sorry I can't explain your situation better.

 

Indeed, it does sound like your truck may have been chipped. I tried 93 octane in my 04 before the programer and it made no difference in the way it ran. Now with the programer, if I don't run the higher octane fuels, it pings and runs like crap. Check your computer and see if there's a jet piggybacking on there.

 

No, actually my engine suffered from the same thing before i "fixed it." I it's not the imaginary butt dyno effect. i ran, and still run Sunoco 93 in mine all the time. It never ran good on 87. It needed a minimum of 89 to no high idel or rough idle. You will have an increase in torque, and a small increase in hp, but i found if you floor it, it all goes away.

 

But Alan, your truck is far from stock, you don't even know the amount of tunning your cousins did to get your systems dialed in together. Your truck should run like crap on 87. Or are you talking about before you did anything to it as far as your mods?

 

Yea, but before it had all the mods, when i rolled it off the parking lot, and was driving a normal ranger, it still ran best on 89-91 octain. Not 87 like it was designed to. I'ld run 93 in the summer months when the tubo was on to help keep it cool. I think i need a bigger radiator for this summer too. Thanls fopr reminding me.

 

An oil cooler maybe a good idea to, not only will it keep the oil temp down, but in turn will help reduce over all engine temps. Those turbo's make for hot engines. Summit has some nice 4-core aluminum radiators at a decent price, that and an oil cooler should do the trick. If you end up going with an auto, don't forget to get you a good tranny cooler as well.

 

I've recently tried 93 octane, and I am getting about 2 more miles to the gallon and a smoother engine performance. It's not a big difference, but it's better.

 

So how do I check to see if I have a chip riding with me? I've never dabbled with the on-board computer and have no idea where it is. I don't even have the Ford manual for this thing.

 

damajikninja - Your computer is probably on the passenger side floor behind the plastic trim on the side under the glove box. I don't have any kind of chip on mine so I can't tell you what to look for. Maybe if you look at some of the web sites that sell chips you will get the idea of how they are set up in your truck.

Also, RangerPilot was pretty much dead on with the description of how different octane fuel acts. Just remember there is nothing magical about premium fuel, it is no cleaner, better, no extra power, etc.... There is no need to run premium fuel in ANY low compression naturally aspirated vehicle when the factory specified 87 as the proper grade. The octane rating in simple terms is it's resistance to burn/ignite. IE - It takes more cyl pressure to ignite 93 octane fuel than it does 87. Which is why low compression engines suffer a loss in performance & economy using premium since the engine has to "work harder" to burn the fuel. On the mechanical side of things if your engine has a compression ratio below ~9.9:1cr, then it was designed to run 87. Again this is in general and not a hard-n-fast rule

As for "why does your truck (and others) feel like it runs better on premium?" That depends on a lot of things. As the others pointed out, the computer's program can have a lot to do with it, as well as the amount of build-up in the engine, or even the general condition of the tune + sensors. If the computer's program has been altered the engine may not "act properly" unless fed premium. I do remember reading something at one point that talked about the factory computer having an incorrect program on it. In other words the factory had designed the truck to run normally on 87 and the division that made the programs for the computer "didn't get the memo". This is purely based off memory, so maybe someone else knows more about it, but I thought it did involve the 4.0L.

 

I haven't heard anything of that G2...I'd love to do a little investigating though, so I'll poke around some and see if I can find that.

If the computer is chipped it will be quite obvious, instead of the computer being a solid box, it'll have a large chip sticking out of one side. I'll see if I can find a picture.

 

The computer is right behind your ashtray area fyi

 

i thought thats what that was... theres a little think there that looks like a hard drive out of a computer. So thats command central on my truck huh?

looks like I'll have to unscrew a few things to look it over. I will check and get back with you...