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?

 

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...

 

What he said 4.7 87 fine 5.7hemi you should be using 89 anyway. And also if you have a hemi most of them have a tick on startups its normal and nothing to worry about I would say 80% of the guys with hemis have the tick

 

If you do have the 4.7, its probably an exhaust leak. I had that problem a couple of times with my 4.7.

 

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.

 

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...

 

But Hammer, don't you like to speculate and guess? So much more exciting.

 

Thanks for the tips. I will give them a check this weekend, its pouring down the rain, and will be snowing tomorrow. Will do on the profile, thanks again.

 

You know what works wonders for finding ticks. Stethoscopes like what a doctor uses, these aren't common but you can use a homemade one like a 1/2 inch PVC pipe place it on the valve cover intake cover if nothing then keep trying till you spot the tick louder this will slim it down.

 

Is it written somewhere that you should use 89 in a hemi? I am at 92k miles and probably 89k of that has been on 87 octane with10% ethanol. No knocking or pinging or other ill effects for me.