4.0 Detonating/Knocking While Accelerating...Help! - Page 2 - JeepForum.com
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Unread 02-11-2013, 04:18 PM   #16
95yj0645
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1995 YJ Wrangler 
 
Join Date: May 2010
Location: indiana
Posts: 363
My apologies I was under the impression you could adjust ignition timing via the distributor. I thought that the coil pack 4.0's with the goofy cam sensor were the non adjustable without the fancy Chrysler scan tool. Good to know.

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Unread 02-11-2013, 05:15 PM   #17
Stingray427
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Join Date: Jan 2010
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Quote:
Originally Posted by jsawduste View Post
Intake Air Temp sensor. Single wire sensor by the throttle body on top of the intake manifold.

Moving it from the hot intake manifold to the cooler airbox tricks the ECM into thinking the incoming intake charge is cooler. The ECM algorithm reads the sensor signal then pumps more fuel by increasing the injector duty cycle........Time the injector is open.........

I`ve seen folks simply drill a hole in the airbox and epoxy the sensor in. I turned an aluminum bung on a lathe then welded it to my cold air intake tube. Guessing your set up is a little different though.

http://www.angelfire.com/my/fan/IAT_sensor.html

http://markism.net/jeep_IAT_relocate.html
Cool, thank you for the info.

A few quick (but probably stupid) questions:

1. Does this work well on stock 4.0's (in case mine is not a stroker)?
2. I assume that it is reversible if need be?
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Unread 02-11-2013, 05:49 PM   #18
laybackman
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1995 YJ Wrangler 
 
Join Date: Dec 2002
Location: Massachusetts
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Quote:
Originally Posted by Stingray427 View Post
My Jeep runs great thankfully but I have noticed that I am getting a slight detonation/knocking sound when accelerating. I know these things are computer controlled so I guess you can adjust the timing but it sounds like it may be doing some damage so I am wondering what to do.

Everyone says premium fuel is a waste of money in these things but I am wondering if the lower octane fuel is part or all of the problem, any thoughts?
I did not read any of the posts but if you are not running the lowest octane fuel you can buy you caused the detonation.

High octane in fuel is there to make the fuel HARDER to burn. Designed for higher comression engines which you do not have.
Fuel with higher cetane burns easier but the gas companies control that chemical additive.
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Unread 02-11-2013, 06:04 PM   #19
Que89YJ
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1989 YJ Wrangler 
 
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Higher octane will reduce knock. The fact you are running 100 mph makes me think that things are not stock somehow. Did you check your codes? If you move the sensor to a cooker temp with the engine running hotter it will run a more advanced curve. I think out is the opposite of what you want to do.
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Unread 02-11-2013, 07:15 PM   #20
jsawduste
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2006 YJ Wrangler 
 
Join Date: Jul 2006
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Quote:
Originally Posted by Que89YJ View Post
Higher octane will reduce knock. The fact you are running 100 mph makes me think that things are not stock somehow. Did you check your codes? If you move the sensor to a cooker temp with the engine running hotter it will run a more advanced curve. I think out is the opposite of what you want to do.
You are correct in that the advance curve will be affected. To the positive side. I am suspecting that a little additional fuel MAY over ride the slight timing advance relocating the IAT will give. If not the mod is easily reverse-able.

Higher octane fuel is NOT harder to burn. It simply burns at a slower rate (slower flame front) as the octane level goes up. Depending on the additive package is MAY run cooler also but that is a wide generic statement. Cylinder pressure can be that of compression but also timing. Both ignition and valve. Many of today's modern engines run a high(er) compression but still get away with 87 octane fuel. There are way to many factors to consider then what an internet forum is worth.
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