Questions about fuel

andyj

andyj

TJ Enthusiast
Joined
Oct 11, 2020
Messages
157
Location
adelaide
Hi Everybody,

I just joined this forum, although I own my TJ for quite some time. It is my second one actually, I bought my first TJ in 1998 in Germany and this one about three years ago here in Australia. I never had any issues, except only recently when I switched to ULP 91 octane. I was using that kind of fuel in Germany without any problems. I tried E10 for some time (it has 95 octane here in SA) and it was OK'ish). The manual (that's one from the 2004 model) says:


"Your engine is designed to meet all emissions regulations and provide excellent
fuel economy and performance when using high quality unleaded gasoline having
an octane rating of 87. The use of premium
gasoline is not recommended. The use of
premium gasoline will provide no benefit over high
quality regular gasoline, and in some circumstances may
result in poorer performance."


My idea was that the 91 octane fuel should be just fine, however the engine is knocking quite a bit. I asked a mechanic and he said that I have to use premium 95 or even 98 octane, no matter what the manual says. The manual on the other hand says the use of premium may result in poorer performance.

I'm somehow at a loss now; how could premium fuel result in poorer performance? And what fuel does the Wrangler actually need? Or is it that the fuel in SA doesn't have 91 octane but actually less? Maybe we get ripped off, I'd not be too surprised...

Or maybe the knocking is not normal and something else maybe the culprit? I'd like to stick to the 91 octane fuel, we wouldn't get any premium fuel in the outback anyway. Any advice?

Cheers,
Andreas
 
That gasoline with the added Alcohol will give poor vehicle performance and gas mileage.
Here in Southern California almost all the gasoline has alcohol with additives which decreases miles per gallon and lowers engine performance. When I leave California and drive to the next state; the miles per gallon goes up 2 sometimes 3 miles to the gallon and there is a noticeable increase in engine performance.
 
I didn't know about the Octane boost - that's certainly an option when traveling the outback.
 
Octane ratings in different countries are different. I was in Japan and their 98 was about equal to 'murican 92 for example. I don't know all the different standards, but yes, it's RON or MON or some crazy equation averaging the two which is what we use here I believe.
 
https://en.m.wikipedia.org/wiki/Octane_rating
"Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's sensitivity,[5] and is not typically published for those countries that use the Anti-Knock Index labelling system.

See the table in the following section for a comparison."
 
So basically 87 AKI used in the US is the equivalent to 91 RON here in AUS. Which makes it work "just so" and not a lot better as I thought. I guess I've to use premium then.
 
andyj said:
So basically 87 AKI used in the US is the equivalent to 91 RON here in AUS. Which makes it work "just so" and not a lot better as I thought. I guess I've to use premium then.
Click to expand...

Interesting you are having issues with 91, I run it all the time with no problems. Unless 91 in Queensland is different (doubt it) I'd say you are having another issue and fuel exacerbates.

Do you have any engine codes popping up?
 
I didn't have any issues in NSW last year; I suspect South Aussies get ripped off. ULP (normal) in Germany has 91 RON as well; it worked perfectly fine for my Wrangler there.
I do have an issue with an oxygen sensor though (P1195) that I'll get fixed next week. The mechanic says it is 99% the sensor itself, because this is an intermittent issue. The engine code pops up and goes away. Right now it doesn't show anything. I'll see if that makes any difference.

I filled up with premium 95 yesterday (on an almost empty tank) and the car runs like a charm. It's a bit more expensive but I don't mind if that's what's required. I switched only recently from E10 to ULP because the car needs almost a liter less per 100km using ULP. But the 91 ULP caused the knocking, E10 has 95 octane here.
 
FWIW I only use 98 and if it costs a little more so be it. you 'should' get better consumption on 98 than the E10 type of fuels.

I've also found that having the engine maintained well will reap the rewards with fuel consumption. A recent trip towing a 700kg camper at 100-110km/h was around 15.5l/100km. Thats with 33's, 4.56 gears with a 6 speed.
 
Roger that. Yep. I wonder what the combustion chambers look like. Might be worth trying a course of Seafoam or something similar. I have a bottle of Mopar combustion chamber cleaner I've been waiting to try on my Oldsmobile just for shits and giggles.
 
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