I bought a new '08 1500 4.7L 6 speed back in August. The engine make kind of a diseal noise at ideal, I'm new to dodge and Hemi's but i gues its the "Hemi tick". While driving along with RPM around 2300-2500 throw the coal to it and it starts sounding like detonation is happening. I normal ran 87 octane in it like the owner manual say the engine is manufacture to run on. But the other day with cheaper gas prices i put in 89 octane....thats when the detonation sounds started. It has used 87 oct at the same station before with no problems. Any one had/have similar occurences.

 

Correction while running at about 2K RPM then throw the coal to it, it starts doing it around 2300 to 2500 RPM.

 

Well, the 4.7 isn't a Hemi so you don't have the Hemi tick. The 5.7 is a Hemi.
You could have just gotten some bad/old gas. It should not ping on 89 octane.

Oh and welcome fellow Kentuckian Louisville here.

 

Have the hemi 5.7 now, but had the older designed 4.7 before in mine (Had the Dakota 2000 with the 4.7 and 5 speed)... I noted that I got terrible ping/knock with cheap gas (87 octane generic) in mine (probably hasn't changed in them since) They upped the horsepower since then, and probably the compression (therefore making it more noticable)...

That Truck , ran best on brand name 89 octane (despite it saying it'll run better on 87)... It'd only do it under load though, low RPMs say, going up a mountain... as mine was a manual, it was usually a load, and lack of downshifting where it'd appear.

Try a fresh tank of 89 first before it goes to the shop.

 

Isn't the new 2008 4.7 310 HP, a "Semi" Hemi, it even has dual plugs.

 

I have the same exact truck you do and ive never heard a noise like that. Just try what everyone is saying about gas, that should do it. i run 93 on mine because i have a chip and it runs great.

 

Hemi refers to the shape of the heads (hemishperical combustion chamber). To my knowledge the 4.7 is not.

 

No, it is a SOHC design. With a Hemi style head, the valves sit across from each other with the spark plug in the top center of the chambers. The 4.7 is more of a Wedge type design with the valves all lined up in a row and the camshaft is in the center of the head.

 

Just kidding,I was just quoting the AllPar website: http://www.allpar.com/mopar/47.html

 

I understand I don't have a HEMI, I was I guess trying to assiociate a sound with something. It made a lite diesel sound when it was brand new, well it had 12 miles on when I test drove it and had 16 when I bought it. It still does it 3000+ miles later but it wasn't until I put the 89 in it did I start hearing what I think is detonation. I haven't driven it that hard either enought to isolate a distinct pattern concerning octane v/s supplier. London, KY here.