94 octane making ze run rich?

MX-3 Money · Post by **MX-3 Money** » August 16th, 2005, 12:06 am

Ok so heres the story, I always run 94 octane in my ze ever since I got it. I just installed a air/fuel gauge cuz i thought I was running rich, and I am. So I changed my oxygen sensors, helped a little bit. So tonight I was running low on gas and nowhere near a sunoco so I could get some 94. Instead I pull into shell and get some 91. Well when I start driving again it seems to be running more normal, only just barly goings into the rich. Even when I put a full load on it. SO would running 94 be my problem, since it takes more heat to ignite it? Plus what all you other ze guys running?

jschrauwen · Post by **jschrauwen** » August 16th, 2005, 12:32 am

I'd be more curious to see what your plugs look like. A good high rpm spirited run and returning home avoiding as much as possible any periods of idle at all and quickly shutting down the engine. Of course wait for it to cool a bit and pull all of the plugs and then tell us what sort of burn you're getting then. A few spark plug sites will give descriptive pics as to what kind of burn/mixture you are encountering by comparing your plugs to their pics. Try that as a comfirmation.

PS: A dirty or old air filter could also give you a rich condition.

MX-3 Money · Post by **MX-3 Money** » August 16th, 2005, 12:48 am

changed my plugs about a month ago, they looked pretty normal with justa bit of white near the ends if I can remember. Also cleaned my air filter not to long ago. I'm going off the info I see on my air/fuel gauge.

lakersfan1 · Post by **lakersfan1** » August 16th, 2005, 8:36 am

Well, the higher the octane, the harder it is to burn the whole mixture. I've always suspected my KL with 10:1 pistons ran a little better on mid-grade than premium.

UKMX-3 · Post by **UKMX-3** » August 16th, 2005, 9:04 am

Bizarre, I thought higher Octane fuels burned more Easily/Vigourously,

Is the energy required for ignition directly proportional to the Octane rating?

what your saying is lower octane fuels burn easier ( but with less energy, and more complete burning)

And Higher octane fuels require more energy to ignite (but with more energy and less complete burning)

Im confused, was my chemistry teacher high when he took my class, maybe i wasnt paying attention!

UKMX-3 · Post by **UKMX-3** » August 16th, 2005, 9:09 am

BTW.

My car runs way better on Super 97RON than it does on standard 94RON.

Maybe UK cars have the same tuning that the High Octane JDM cars have

lakersfan1 · Post by **lakersfan1** » August 16th, 2005, 9:38 am

UKMX-3 wrote:Is the energy required for ignition directly proportional to the Octane rating?

what your saying is lower octane fuels burn easier ( but with less energy, and more complete burning)

And Higher octane fuels require more energy to ignite (but with more energy and less complete burning)

Correct. Engines with higher compression and/or higher combustion chamber temperatures require higher octane. Why? The higher the compression, the easier fuel will ignite. The higher the combustion chamber temps, the easier the fuel will ignite. What you don't want, however, is the fuel to ignite from the heat and compression in the engine alone. You want it to ignite from the spark plugs in coordination with the compression. So if you have a hot combustion chamber and/or too high compression, you need a higher octane fuel so the fuel will wait for the spark plug until the mixture ignites. If the fuel ignites before the spark plug (predetonation), the piston will still be in its compression stroke, so the explosion will try to push the piston back on its compression stroke , going against the crankshaft rotation. Make sense?

UKMX-3 · Post by **UKMX-3** » August 16th, 2005, 10:07 am

Strangely Enough. YES

No wonder its taken over 100 years to get internal combustion working properly!

MX-3 Money · Post by **MX-3 Money** » August 16th, 2005, 12:01 pm

UKMX-3 wrote:Strangely Enough. YES

No wonder its taken over 100 years to get internal combustion working properly!

So does that make sence, lowering my octane level makes my car run way less rich?

UKMX-3 · Post by **UKMX-3** » August 16th, 2005, 12:10 pm

Yes because you get a more complete burning of the fuel!
Presto chango - Its Magic!

MX-3 Money · Post by **MX-3 Money** » August 16th, 2005, 11:34 pm

Well I guess that wasn't really it tho. I went and filled up with 91 today and it started running rich again. I guess last night since I ony put in 5 liters it started running normal cuz there wasn't that much gas in my tank??? I don't know. So why the hell am i running rich?!?!? My gauge goes all the way into rich even when I just put 25-50% load on it. I know that when I put a hevy load (75%) its supposed to go into the rich no mater what, but i don't have to put anywhere near that much. What can i do? Would a lower fuel pressure work, or higher? I don't know...I'm lost.

jschrauwen · Post by **jschrauwen** » August 17th, 2005, 12:10 am

Brad, do you or have you, or even just recently let your gas tank level go down to almost bone dry. if yes to any than there may be part of the problem. There's going to be (over years and car is 12 years old) a build up of moisture and liquids (mostly water and crap) in the gas tank. By rights this stuff is heavier than gas and will settle at the bottom of the tank which is no biggy, ...... unless you let it run to almost bone dry because the fuel pump which normally takes it's fuel from the upper levels of the gas tank will now be scooping up that "crap". Again just a possibility. Your initial thread said that you thought that you were running rich and this motivated you to install a guage. I was of nearly the same premise but discounted that theory because of the confirmation by the spark plugs. Where is or what makes you believe that it's running rich? Aside from the guage? Is it because you have enormous clouds of black smoke from the exhaust, excessive black soot on the inside of the tailpipe? Get the tank topped up, say Sunoco 94 again, since it's been used to that and that was the environment you were in when you encountered this problem and we'll go from there. Last time you cleaned the air filter, you re-oiled it again right? Last time you changed the fuel filter?? Which plugs are you using - type/number? The re-usable air filter, is it a K&N in the stock airbox or a CAI set-up. If CAI, is it routed into the inside cavity of the drivers side fender? If not this may be a contributer also.

MX-3 Money · Post by **MX-3 Money** » August 17th, 2005, 1:22 am

Ok so I have let my tank go pretty low, i try to get as much out of it before i fork out more money. Well the whole reason I thought I was running rich is cuz back about 6 months I went and got my car dynoed and only had 124hp at the wheels and the computer said I was running way to rich. Plus I do have black soot on the exhaust that i installed when i got my ze. Everytime I top up with 94 it still runs rich. Changed my fuel filter last fall. I was running BKR6E-11 plugs but i switched to BKR5E-11. I have the cai of ebay and it is over by the fender. I'll try cleanging the filter again with some k&n cleaner, you can get that at canadian tire right? I guess i'll try the high rpm sprints and check the plugs on the weekend when I get some time. Buy hey thanks john for your help!

jschrauwen · Post by **jschrauwen** » August 17th, 2005, 1:53 am

MX-3 Money wrote:Ok so I have let my tank go pretty low, i try to get as much out of it before i fork out more money.
You'll get the same mileage regardless of when you fill up and spend the same amount of money depending on how much you drive. I've made it a habit on the MX never to let it get below 1/4 for those very reasons i mentioned earlier. You'll be digging into your pocket more often but not spending any more money in the long run. Besides, what's money your "MX-3 Money" right ... LOL

Well the whole reason I thought I was running rich is cuz back about 6 months I went and got my car dynoed and only had 124hp at the wheels and the computer said I was running way to rich.
Adequate and correct air availability can be a contributer to lean/rich mixtures. Is the insides of your VAF completely clean and wiped dry and does it move freely without stumble or friction? How clean is your TB? have you done an overhaul on that? It's actually quite easy. Mine was really gunked up and especially the air idle sdjust screw was severly gunked and carboned up. These possible restrictions to air intake could also be a factor. Has the IM been cleaned out?

Plus I do have black soot on the exhaust that i installed when i got my ze. Everytime I top up with 94 it still runs rich.
So I take it that after you top up with 94 you wipe out the inside of the tailpipe and later confirm that it's sooted up again?

Changed my fuel filter last fall.
Good show!

I was running BKR6E-11 plugs but i switched to BKR5E-11.
Why, please elaborate your motivation for this move?

I have the cai of ebay and it is over by the fender.
Over the fender?? OK, so it's not inside the fender well or you would have said that. This being the case, you're sucking in a shatload of extremely hot air which is detrimental of effective combustion. Like the name implies - COLD air intake, not hot air intake. This could be one of the factors for poor hp and a rich condition if not the biggest.

I'll try cleanging the filter again with some k&n cleaner, you can get that at canadian tire right?
Yes, oil filter cleaner and the spray on oil for after. It's in a kit I believe.

I guess i'll try the high rpm sprints and check the plugs on the weekend when I get some time.
Good plan. A good run on the 401 or similar for about 10 minutes at least and the quickest way home without having the engine edle for any period of time (stoplights). Referred to in the bike world as a plug chop. Actually, if your going to dyno again, that's a good time to experiment with different plugs as well as other engine management controls. That's the ideal way to verify and correct those niggley's.

Buy hey thanks john for your help!
Any time time Brad

bigtime · Post by **bigtime** » August 17th, 2005, 10:23 am

japans worst fuel is 100 octane

they got like 104 or so also
in australia you can get 91, 95 or 98 octane on pump.
all very expensive at the moment