What to do
#1
What to do
I bought my 08 used with 55000 on it. Every since I bought it, it has sort of a knock when I first start it up of the morning, but goes away as it warms up. Well, I wondered if it was my 87 octane gas I was using. I tried putting in 89 octane, and that cut it back immensely. I am thinking about now trying 91 in it to see what it does. But here is my problem. I was looking in the down at the programing outlet, and noticed the harness was loose, like someone had been using it, with a fair amount of ware to it. I am wondering if someone may have used a programer on it, and set it to a higher octane tune, and that's why it sounds so bad with a lower octane. I can tell a good difference in driving when merging in traffic with the different gas.
Is there a way I can find if it has had a different tune set, without buying a chip? Can I hurt anything if I run a lower octane than what it was tuned for?
Is there a way I can find if it has had a different tune set, without buying a chip? Can I hurt anything if I run a lower octane than what it was tuned for?
#2
Join Date: Jul 2007
Location: South Georgia/East Florida
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A dealer can hook up the StarScan tool and tell if there is a tune on it. If this is a 4.7 then 87 is fine, if this is a Hemi we are talking about YOU SHOULD BE USING 89 OCTANE fuel anyway and this may be your problem. I'm hoping sustained use of 87 and all the pre-detonation you've experienced hasn't done damage to the cylinders.
BTW, if stock tune, there is NO reason to use 91 octane although it won't hurt anything...
BTW, if stock tune, there is NO reason to use 91 octane although it won't hurt anything...
#3
A dealer can hook up the StarScan tool and tell if there is a tune on it. If this is a 4.7 then 87 is fine, if this is a Hemi we are talking about YOU SHOULD BE USING 89 OCTANE fuel anyway and this may be your problem. I'm hoping sustained use of 87 and all the pre-detonation you've experienced hasn't done damage to the cylinders.
BTW, if stock tune, there is NO reason to use 91 octane although it won't hurt anything...
BTW, if stock tune, there is NO reason to use 91 octane although it won't hurt anything...
#5
Its not a Hemi. I noticed this morning, that it does it on mostly on the first start of of the day, and its when the start program has the increased rpms, and with lower octane, its worse. When it kicks down after about 45 seconds, it pretty much quits. If I manually give it gas, it does not do it, odd. Day after tomorrow, I am going to fill up with 91 just to see what happens, whats a 7 dollar experiment lol. Next month, I hope to take it and have an 18" Magnaflow installed, with dual exits. I will have the shop check for any other possible leaks. Thanks for the tips. Anything else you can think of to check, let me know.
#6
Join Date: Jul 2007
Location: South Georgia/East Florida
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OK, 4.7... It has NOTHING to do with the gas. Check the manifold bolts, probably on the driver's side. The 4.7 is notorious for having them snap off at the head. Time, heat and vibration causes them to fail. The symptoms fit perfectly. When the engine is cold, there is no seal and the manifold is slapping against the engine, causing your "knock". As engine temperature increases, the gasket swells and takes up the space, so the "knock" stops or at least is much fainter. VERY COMMON ISSUE.
Luckily, these bolts almost always break at the head and there is enough thread to get a hold of them and get them out without having to use any type of extractor...
BTW, you should put your vehicle information in your profile, I would have figured this out yesterday... LOL...
Luckily, these bolts almost always break at the head and there is enough thread to get a hold of them and get them out without having to use any type of extractor...
BTW, you should put your vehicle information in your profile, I would have figured this out yesterday... LOL...
Last edited by HammerZ71; 01-16-2012 at 05:14 PM.
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