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Knock on 91 octane. None at 94 octane

 
Old 05-23-2019, 12:31 PM
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Knock on 91 octane. None at 94 octane

Hi Everyone.

I have a bone stock 2010 SH-AWD 6MT.

I get an annoying knock with 91 octane fuel, even when the ambient temperature is only 10 degrees Celsius outside.

This is true for a few brands of fuel I've used (Costco, Shell, Esso, Petro-Canada)

I've noticed the knock goes away entirely using the 94 octane fuel I've found (Petro-Canada)

The rub is that 94 octane is expensive, and reduces my fuel economy by roughly 10%.


Question: From anyone's experience, is it sustainable to use Octane booster regularly? Will I experience any fouling issues?

The $7.00 cost per bottle is cheaper than the price differential for 94 octane, per tank.

Thank you
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Old 05-23-2019, 03:41 PM
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A few thoughts and comments:
  • In Canada, as with the U.S., there is no such a thing as a fuel marketed as 91 or 94 octane; they are 91 AKI and 94 AKI (yes, I know, splitting a hair, but I prefer to be precise).
  • When you experience the knock on 91 AKI fuel, is there a typical driving environment where it happens more than others (say low RPMs, high gear selection, high throttle setting)?
  • Running octane booster on a regular basis is a bad idea for the very reason you listed.
  • Long story short, it would probably be best to figure out why your engine is pinging on the recommended fuel.
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Old 05-23-2019, 04:15 PM
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Thank you for your input. The knock is occurring at low rpm, mostly on 1st gear take off.

Also, it's funny. Petro Canada refers to their fuel as 94 octane. I've never heard of AKI? https://www.petro-canada.ca/en/personal/fuel/gas

"We offer three gasoline grades across the country, each with a different octane number 87, 89 and 91. Many of our stations in Alberta, Ontario and Quebec also offer 94 octane gas, which is the highest level of octane available in Canada."

I think you're right though about finding the source of the knock. I am currently in the queue for the rebuilt engine recall. I wonder if my pre-cats and main cat are requiring replacement from all of the blow by over the past 10 years?

Last edited by coldb; 05-23-2019 at 04:17 PM.
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Old 05-23-2019, 06:11 PM
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Originally Posted by coldb View Post
Thank you for your input. The knock is occurring at low rpm, mostly on 1st gear take off.

Also, it's funny. Petro Canada refers to their fuel as 94 octane. I've never heard of AKI? https://www.petro-canada.ca/en/personal/fuel/gas

"We offer three gasoline grades across the country, each with a different octane number 87, 89 and 91. Many of our stations in Alberta, Ontario and Quebec also offer 94 octane gas, which is the highest level of octane available in Canada."

I think you're right though about finding the source of the knock. I am currently in the queue for the rebuilt engine recall. I wonder if my pre-cats and main cat are requiring replacement from all of the blow by over the past 10 years?
Look in the "Measurement methods", Canada does not use RON or MON, they use AKI:
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Old 05-24-2019, 09:31 AM
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I am not sure if you are getting the knock and rattle mixed up but since you said it occurs at low RPMs, it could be your engine oil level too.
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Old 05-24-2019, 09:43 AM
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The 3.5L is also prone to lower-RPM knocking. I've experienced knock at low RPM's on occasion, yet virtually never at higher RPM's (when monitored by KTuner or Torque Pro). I find if I just keep it tuned up it does it less. I know some of these carbon-cleaning products are sometimes considered a farce but I seem to experience it less for a few thousand miles when I use Seafoam through the intake or Gumout Multi-System tune-up. Being that the 3.7 is prone to oil consumption, carbon buildup might be a bigger issue and add to the problem.

I pointed it out to Kenny at Turbogixxer who is doing my e-tunes. He asked that I log it then send it over for him to look at. I haven't done that yet but once I do, he might be able to provide an updated map that pulls timing a bit or adjusts the A/F ratio to compensate. We'll see.
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Old 05-30-2019, 07:32 PM
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Yeah, good thought on carbon build up from oil consumption adding to the need for high octane.
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Old 05-31-2019, 03:43 PM
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add a meth injection system or water injection. Octane boosters work by .1's of a point raise so "raise by few points" could litterally mean a boost from 91AKI to 91.5 AKI. Meth/Water injection are much better esp in hot temps.
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