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Engine Knock with 93 Octane??

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Old Jun 29, 2010 | 05:18 PM
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Default Engine Knock with 93 Octane??

Trying to figure out why i need 100 octane in order for my motor not to knock?

It's pretty much stock minus just a few mod's,like slp air lid,k&n air filter,160 thermostat,superchips handheld tuner <knocks with stock or performance tune> flowmaster muffler,3.73 gears,no cats,descreened mass airflow,coolant bypass,transgo reprograming shift kit....

I have tried amoco ultra sunoco 93 mobil 93 you name it i have tried it,and under wot the car pings pretty badly and i know thats not right.

The car was a 1 owner upto 1 yr ago and Never raced until i bought it and unless i have 100 in the tank it pings.

I have no check engine light on and was hoping someone could point me in the right direction??

Thanks in advance for your time...
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Old Jun 29, 2010 | 05:39 PM
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Could be oil mist from the PCV system getting into the intake and causing the ping. Install a catch can and see if your problem goes away.
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Old Jun 29, 2010 | 05:59 PM
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i never thought of that,i will try and let you know..

Thanks again for your interest to assist me...
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Old Jun 29, 2010 | 07:21 PM
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Yep, carboned up from sucking oil... might need to do some topend cleaner (or give it a drink).

Another cause might be the descreened MAF... ever put a wideband on it to see what the fueling looks like?
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Old Jun 29, 2010 | 09:47 PM
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Not yet,im looking to find a local shop to take the car to but have not found one as of yet.

Where can i purchase a wideband tool that you mentioned in your post?

Thanks again for your time
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Old Jun 29, 2010 | 10:00 PM
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+1 on the descreened MAF. It's best to re-scale the MAF table after descreening. Can get away without doing it, but, is better to be done.

A wideband 02 sensor is used to measure air/fuel ratio. You need the wideband sensor & the display or controller.

Top end cleaner like Sea-foam
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Old Jun 30, 2010 | 05:48 AM
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Personally, I like my Innovate LM2 wideband - but if you are going to have it tuned, you don't need to buy your own...

I would get another stock MAF and replace yours - no gains to be had from taking the screen out on a setup like yours... all you do is run the risk of skewing the fueling.

Decarbon the chambers with Sea-foam top end cleaner... or you can use the old-school trick of sucking a glass of water through a drinking straw with the brake booster vacuum line (hold the RPM at around 3k while doing it)...
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Old Jun 30, 2010 | 08:19 AM
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get some seafoam, and clean up those heads
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Carbon build up, as others have stated.

Another thing to look out for is oil from you K&N contaminating your MAF hot wires. If the oil from the air cleaner gets on them, it will bake on, and cause an insulating effect, which in turn causes the maf to read very lean, and the fuel trims to shoot way up to compensate.
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Old Jun 30, 2010 | 09:21 AM
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If you have a scan tool, start looking at the misfire
(current, cylinder mode) counts. See if any holes
are way out of bed with the rest, which might point
to a silted-up injector or two.

Check for cleverness like !EGR without tuning out the
EGR advance; this is a good way to get light-throttle
ping.
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