Hey guys as some of you may know i drive a 99 dodge ram SLT 5.9. I got the truck last year from an old man and it had 38K miles on it. It currently has 46K and since I've had it its had a small knocking noise when I accelerated until about 45 mph. I thought it was the plenum possibly, but when i checked it was clean as a whistle. The other day I put in premium for the first time since i had it and the knocking went away. My question is, is the reason because of the higher octane? I don't know much about engines so I don't know if this is the reason. Based on how well the truck is driving since I've filled up I will def. be using 93 now instead of 89.

 

Probably hearing spark knock.. hopefully there wasnt any damage done..

 

If you were getting spark knock on 89...... there is something amiss there. These engines were designed to run on 87......

Did you pull the throttle body to check the plenum??

 

May wanna check for a clogged cat too

 

I did not pull the TB I just looked through with a flash light and it was completely clean from what I could see which was most of the pan except for the edges.

 

I suggest you remove the TB and look in the corners for oil pooling. Also if the precat o2 has never been changed there is a good chance the cat is getting clogged from that, let alone the plenum.

 

+1 on removing the TB. I thought mine was fine until I removed the TB. Clean it and the iac valve too while its off, if you haven't already.

 

Regardless if the plenum is clean I would change it out. It will eventually be a problem down the road.

 

Ok I'll pull the TB and recheck and I'll clean it while I'm at it. I will hopefully be replacing the Plenum within the next month or so. While doing more research I saw the end all plenum thread and I will be pulling the precat o2 sensor and see if I notice a difference and whether I need to replace the cat. while watching the video that was on that thread the guy mentioned that if your vehicle has less than 70k miles or is less than 7 years old that I can get it replaced because of the federal warranty. Will this apply to me since my truck only has 46K on it or do both requirements have to be filled?

 

If it's over 7 years old, they won't warranty it.