interesting question about octane...from TruckTrend...

[jwyshrek]

To Premium or Not To Premium
Q: I want to buy an FJ Cruiser but it calls for premium fuel. This is an issue for me, as premium fuel is 25 cents more per gallon than regular. Can this vehicle run on regular gas, or can it be tuned to run on regular gas?

A: The 2007 FJ Cruiser is the same basic platform as Toyota's 4Runner SUV, and both use the very same 4.0-liter V-6 engine. So why does the 4Runner owner's manual stipulate a minimum of 87 octane (regular gas) while FJ specifications read 91 or better? Good question. According to David Lee, product education administrator at the University of Toyota, Toyota wanted the new FJ Cruiser to meet the more stringent LEV II (Low-Emission Vehicle) standards, which it was able to achieve, but only while running its V-6 on a 91 octane or higher-rated fuel. Therefore, in order to be officially deemed an LEV II vehicle, 91 octane had to be listed as the required minimum. The good news: you can run the FJ on regular gas without any significant ill effects (spark knock, loss of power), just like the V-6 4Runner (LEV I). The only differences will be a tiny bit increased emissions and an iota less power. On the dynamometer, the higher octane increases engine output by six horsepower and 10 pound-feet of torque at peak rpm, but I don't see that being perceptible in real-world driving.

 

[Koz]

Very interesting! I would have to see it to believe 91 octane produces 6hp in the V6. Sounds like :bs:

Koz

 

[Even Steven]

I dont think the article is claiming that 91 octane really produces 6 hp for the V6 engine. I do believe that it is possible for 87 octane gas to REDUCE engine output by 6 hp due to retarded ignition timing.

In other words, the ENGINE produces its maximum hp on the fuel that does not cause a change in ignition timing. I would only find the claim hard to believe if the V6 engine did not pull ignition timing with the lower octane fuel, which seems to be what they are trying to say.

 

[G.I.G.]

Interesting...

I wonder if that holds true with the 4.7L V8 as well? I'll be getting my Runner with the V8 soon and I'd like to avoid paying $3.50 per gallon for premium if possible (not as though $3.25 for regular is good )

 

[RonDeF]

I owned an FJ TRD/SE for 5 months. I can tell you that the FJ runs fine on regular gas (87 Octane) however you will loose some performance and the mpg will be lower. You may or may not notice the performance difference. Before you purchase you should really look at all of the data about broken windshields. The windshields in the FJ are terrible and crack from the tinyest of objects hitting them. They also are having problems with the windshields cracking due to stress. This was one of the reasons I got rid of my FJ. I had three windshields crack in less than 5 months. They are also expensive to replace, approximately $1,400. The other reason I got rid of it was due to my in-laws moving in with us. The FJ does not work as a vehicle for carting around elderly people, one of which is blind.

 

[Koz]

When I see dyno charts that show a hp difference between 87 and 91, I will believe this. I also don't believe timing is being pulled using 87. I'm not a gambling man but I would bet this is BS.

Koz

 

[Even Steven]

When I see dyno charts that show a hp difference between 87 and 91, I will believe this. I also don\'t believe timing is being pulled using 87. I\'m not a gambling man but I would bet this is BS.

Koz

I dont believe the timing is being pulled on a V6 with 87 octane gas either. But if you think about it, under high load conditions it is possible. I am sure it does not happen under regular driving conditions though.

 

[RamThis]

I dont believe the timing is being pulled on a V6 with 87 octane gas either. But if you think about it, under high load conditions it is possible. I am sure it does not happen under regular driving conditions though.

If these engines have a knock sensor, then timing will be pulled when running 87 VS 91 octane fuel. The O2 sensors will also pull timing depending on the quality of the fuel and how much CO's and NO2 are running out the exhaust after ignition. These computers are constantly adapting and if it senses a higher than normal knock or engine temp, it will retard timing to compensate. Under light to no-load, you are right, the timing will set about the same for all three grades of fuel. But under acceleration, like on an entrance ramp to the interstate, or pulling out into traffic on a busy street, you might notice a difference between the grades due to the computer retarding the timing. I know I notice it in my Ram, especially when I switched to the Mopar Performance PCM. I ran 91 in it the first few tanks until the truck had been through a few good drive cycles and the PCM had learned and compensated for all variables. I then tried 87 octane for a tank. It ran horrible. No power, and had a ping that sounded like someone put ball bearings down the spark plug holes under medium acceleration (No knock sensor to compensate for that on the Rams) Went back to the 91 and all was cured.

 

[Even Steven]

RamThis,

Two things-----

1 - Oxygen sensors do not alter ignition timing. They alter fuel mixture.

2 - Someone on this forum posted about recording live data from a scan tool while driving under various conditions with a V6 4Runner. If I remember correctly, his 4Runner did not pull timing using 87 octane under any conditions (even high load), but of course that can vary depending on many variables. Even ambient temperature can make a difference, so I am sure that it is quite possible. The point is that the V6 engine seems to run fine on 87 octane without knocking and causing ignition retardation 99 percent of the time.

 

[RamThis]

RamThis,

Two things-----

1 - Oxygen sensors do not alter ignition timing. They alter fuel mixture.

2 - Someone on this forum posted about recording live data from a scan tool while driving under various conditions with a V6 4Runner. If I remember correctly, his 4Runner did not pull timing using 87 octane under any conditions (even high load), but of course that can vary depending on many variables. Even ambient temperature can make a difference, so I am sure that it is quite possible. The point is that the V6 engine seems to run fine on 87 octane without knocking and causing ignition retardation 99 percent of the time.

Not to argue with you, just trying to clear up my info. I thought that the O2 sensors, through the PCM, could also effect timing, same as the MAP sensor will, EGT, and IAT sensors. Does not the computer use all these readings to adjust timing, as well as fuel trim? Like I said, this is just my understanding of it so if it's wrong please correct me. :

 

[p nut]

To clarify another point:

I have owned cars that say "PREMIUM FUEL REQUIRED" right on the gauge. The FJ owner's manual does not say it REQUIRES premium, but RECOMMENDS it. I believe it states that you can run 85/87 on it, but will lose some performance.

Also on a side note, I am glad I did not pick up an FJ. The windshield issue that they are having is ridiculous. I hope something can be done to resolve this issue (except for that crappy clear-bra-like "shield" they're offering).