Is 91 octane really over kill on a 3rd gen?

[BoomSticks]

Really? This is still a question?

Marketing really works I guess.

If you people won't listen to other members, how about the awesome guys from CarTalk:

Premium vs. Regular Myths

And further FAQ: Premium vs. Regular FAQ

Q. My owner's manual says my car will run just fine on regular, unleaded gas. Will "treating" it to premium gas provide any benefit?


A. Let's be perfectly clear about this:

NO!

A. The only thing you'll be benefiting are the portfolios of impoverished oil company executives.

 

[JayRolla]

I know this thread is dedicated more towards naturally aspirated vehicles but I just wanted to give a quick PSA to those with superchargers that wonder whether or not they can get away with running less than premium fuel. When I first bought my supercharged truck they filled my tank as a "courtesy" with low grade fuel. Through the course of that tank the car ran like crap, I had pinging, and averaged like 16 mpg with a mix of highway/city driving. I ran that completely empty and filled up with 91 and it made an entire world of difference. It ran as smooth as can be, basically no pinging, and I actually averaged nearly 20 mpg with almost identical driving habits from the last tank. Granted like I said before this doesn't really apply to the NA vehicles, as they are built to be able to run on low octane.

I bought a turbo 2.5l dodge shadow to build as a sleeper. Same motor as some of the minivans. It had fuel issues. Dealer replaced fuel pump and filter. Also cleaned them replaced them after that did nothing. They even swapped ecu. I bought it for $1k. Added premium fuel. Issue fixed. All the power was back. It even said premium only on the cap. I modded her up a bit. Very fun sleeper.

 

[kolelt]

My dads Chrysler 300c in the user manual it states only to use higher then regular. And one time I put regular. And it ran like shit.

We have a seadoo rxp supercharged jetski. Seadoo only and highly recommend SUPER.

So I think it does make a difference as the engineers wouldn't just be like, this car will have regular, this car will have premium and so on. There's a reason why the manufacturer is recommending the type of fuel

 

[cmtul]

We started running 87 shortly after buying. Within weeks we noticed sluggish response, and rough idle. Did a complete tune up, and oil change thinking that was the issue. Drove that way for a bit thinking it would settle. Last month we went back to 91, and the rough idle and sluggishness went away after the second tank.

 

[coltonbaxter31]

I usually run 87 but lately I've been running 89 octane ("plus") and my 4Runner seems a bit more peppier and not as slow to get to highway speeds and doesn't struggle as bad getting up steep mountain hills (I'm running 35's) Also gas mileage has gone up about 1 or 2.. My engine just seems to run better on it for now but I don't think it's worth it if you're trying to get better fuel economy. But that's just my opinion. I wouldnt run premium in the 4Runner.


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[jhfleet]

We started running 87 shortly after buying. Within weeks we noticed sluggish response, and rough idle. Did a complete tune up, and oil change thinking that was the issue. Drove that way for a bit thinking it would settle. Last month we went back to 91, and the rough idle and sluggishness went away after the second tank.

Oil change for sluggishness and rough idle? And, what is a "complete tune up".

 

[gamefreakgc]

I know this thread is dedicated more towards naturally aspirated vehicles but I just wanted to give a quick PSA to those with superchargers that wonder whether or not they can get away with running less than premium fuel. When I first bought my supercharged truck they filled my tank as a "courtesy" with low grade fuel. Through the course of that tank the car ran like crap, I had pinging, and averaged like 16 mpg with a mix of highway/city driving. I ran that completely empty and filled up with 91 and it made an entire world of difference. It ran as smooth as can be, basically no pinging, and I actually averaged nearly 20 mpg with almost identical driving habits from the last tank. Granted like I said before this doesn't really apply to the NA vehicles, as they are built to be able to run on low octane.

The supercharger kit when installed new came with a sticker that says "Premium Fuel Only" you are supposed to put near the gas cap. The instructions also say to only use premium fuel. Suppresses pre-detonation.

 

[jhfleet]

I once had a conversation with a fellow who said he carried around a can of jet fuel and added some to his tank at every fill up. He said it made his car run like a hopped-up V8 instead of the four banger it actually had. Plus, it gave tons of extra mpg, ran quieter, and was a real sleeper on the street. Being an airplane mechanic at the time, I hated to tell him that jet fuel was virtually identical to kerosene and worked great in diesel engines. But, bad things would happen and it certainly wouldn't add any performance if a person was dumb enough to use it in a gasoline engine. I suggested he replace the air in his tires with imported air from Tibet for a real performance boost.

 

[Focoty]

The supercharger kit when installed new came with a sticker that says "Premium Fuel Only" you are supposed to put near the gas cap. The instructions also say to only use premium fuel. Suppresses pre-detonation.

Yep I have one sticker on the gas door and one on the dashboard by the diff locker switch. I guess the dealer I bought it from thought that it was just a "suggestion".....

 

[JayRolla]

The supercharger kit when installed new came with a sticker that says "Premium Fuel Only" you are supposed to put near the gas cap. The instructions also say to only use premium fuel. Suppresses pre-detonation.

Its actually suppressing detonation, which is the ignition of spent gas after the normal initial combustion. This after time can cause damage but is not as bad as pre-ignition.

Pre-ignition is when it fires before initial combustion. Which is very bad!!! Usually is caused by completely foul spark plugs or burnt valve. This will eat up valves and pistons very quickly. Tuning of fuel quality has very little affect on pre-ignition.

 

[gamefreakgc]

Its actually suppressing detonation, which is the ignition of spent gas after the normal initial combustion. This after time can cause damage but is not as bad as pre-ignition.

Pre-ignition is when it fires before initial combustion. Which is very bad!!! Usually is caused by completely foul spark plugs or burnt valve. This will eat up valves and pistons very quickly. Tuning of fuel quality has very little affect on pre-ignition.

Well there ya go! So the pinging we hear is detonation? I guess I've heard it explained too many times and not know which is which anymore.

 

[frodiesel]

In a 4runner it is overkill. Now my old all wheel steering turbo mazda626 it absolutely needed premioso petro. Literally burned through two exh valves at 278k miles. Rebuilt the head and gave to a buddy with 310k. I used to have a real turbo626 problem. Once put a yamaha SHO motor in an 88 4ws 626.

Even tho its overkill, my runner earned a tank of premium when it ran outta gas, but limped 3 miles to the station.

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[nevada]

Its actually suppressing detonation, which is the ignition of spent gas after the normal initial combustion. This after time can cause damage but is not as bad as pre-ignition.

Pre-ignition is when it fires before initial combustion. Which is very bad!!! Usually is caused by completely foul spark plugs or burnt valve. This will eat up valves and pistons very quickly. Tuning of fuel quality has very little affect on pre-ignition.

Well there ya go! So the pinging we hear is detonation? I guess I've heard it explained too many times and not know which is which anymore.

here is a pretty good explanation on both. with some nice graphics to go along with it.

https://www.savvyanalysis.com/articles/detonation-and-pre-ignition

I believe this is actually about plane engines, but its still the same process.

 

[JayRolla]

here is a pretty good explanation on both. with some nice graphics to go along with it.

https://www.savvyanalysis.com/articles/detonation-and-pre-ignition

I believe this is actually about plane engines, but its still the same process.

Exactly how it works. I love the way this link explains it. Good stuff.

Pre-ignition is very bad. E85 guys are getting it in over 1000hp applications when your stuff so much fuel into the cylinder that it literally runs out of space and preignites.

 

[wettRunner]

New to the forum

I've only had my 4Runner for a few days now, and I filled it with 87 regular. It's a 99' 3.4l 4WD w/ 180,000 miles. Got a knock that started at idle only. It is inconsistent when hot or cold. Wondering if different fuel/ heavier oil will resolve. Toyota dealer quoted $3,500-$5,000 to fix, and stated it was rod knock.

I had an ej25 boxer engine before that I only ran NO ETHANOL in. Truly believe that no matter what octane, ethanol % is really what damages engines/ gaskets.

 

[phattyduck]

I've only had my 4Runner for a few days now, and I filled it with 87 regular. It's a 99' 3.4l 4WD w/ 180,000 miles. Got a knock that started at idle only. It is inconsistent when hot or cold. Wondering if different fuel/ heavier oil will resolve. Toyota dealer quoted $3,500-$5,000 to fix, and stated it was rod knock.

Knock at idle won't be fuel related... You can try a thicker oil (10w40, maybe even thicker) to see if that quiets it down for a while - but if it is the bearings, something will have to be done sooner rather than later.

-Charlie

 

[gamefreakgc]

I've only had my 4Runner for a few days now, and I filled it with 87 regular. It's a 99' 3.4l 4WD w/ 180,000 miles. Got a knock that started at idle only. It is inconsistent when hot or cold. Wondering if different fuel/ heavier oil will resolve. Toyota dealer quoted $3,500-$5,000 to fix, and stated it was rod knock.

I had an ej25 boxer engine before that I only ran NO ETHANOL in. Truly believe that no matter what octane, ethanol % is really what damages engines/ gaskets.

Yeah if it really is rod knock, try thicker oil or a friction modifier in the oil. Worth a shot since your engine is running on borrowed time.

 

[wettRunner]

Knock at idle won't be fuel related... You can try a thicker oil (10w40, maybe even thicker) to see if that quiets it down for a while - but if it is the bearings, something will have to be done sooner rather than later.

-Charlie

Roger that. Guess ill be looking at used 5VZ-FE motors this week.

The knock is SO inconsistent though. For instance when I got off the highway this morning after 20 mins of both stop and go, and highways speeds, it would knock at 750 RPM's.

I took it out of gear, and put it right back in drive, and miraculously, no knock. But after getting up to speed and slowing down again, the knock returns. (Maybe Flexplate?)

VIDEO LINK****
https://www.youtube.com/watch?v=rcFRWuvVHqY&feature=youtu.be

https://www.youtube.com/watch?v=hcWc0qHRROs

I figured a rod knock would be more consistent once the metals warmed up, but then again, that's why i'm asking you guys for help.

Thank you guys for the reply's.

(maybe there is a better thread for this but since i'm new, I can't post a new thread.)out:

 

[19963.4lsr5]

A cracked flex plate will make the rod knock sound under load. Been there. But usually it only cracks if something is not aligned properly. The could be caused by loose bolts, or missing alignment dowels.


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[nevada]

Roger that. Guess ill be looking at used 5VZ-FE motors this week.

The knock is SO inconsistent though. For instance when I got off the highway this morning after 20 mins of both stop and go, and highways speeds, it would knock at 750 RPM's.

I took it out of gear, and put it right back in drive, and miraculously, no knock. But after getting up to speed and slowing down again, the knock returns. (Maybe Flexplate?)

VIDEO LINK****
https://www.youtube.com/watch?v=rcFRWuvVHqY&feature=youtu.be

https://www.youtube.com/watch?v=hcWc0qHRROs

I figured a rod knock would be more consistent once the metals warmed up, but then again, that's why i'm asking you guys for help.

Thank you guys for the reply's.

(maybe there is a better thread for this but since i'm new, I can't post a new thread.)out:

that isn't a rod knock. if it were a rod, there would be no pause between the knocks. it would be consistent and smooth. do those have an inspection cover on the bottom of the trans? I cant remember. check the converter bolts. ive dealt with something similar before, it had been misdiagnosed several times as a engine bearing knock. in fact they apparently even pulled the engine and rebuilt it, still knocked.

it ended up being the converter bolts. the nuts were bottoming out on the stud(non threaded) section before getting tight against the converter. wrong bolts, or lacking washers. I cant remember now...