I've had an issue with spark knock under load for quite some time on my truck. It doesn't knock when I'm just putting around and commuting, so I haven't been super motivated to diagnose/repair it. It will knock a lot at WOT on 87 octane and 89 octane. On 93 it will knock just a little, but it still knocks.

About 3500 miles ago (roughly around the last time I changed the oil) I installed an oil catch can. It's in line between the PCV valve and the intake manifold. The PCV is an OEM mopar valve and is still fairly new. Changed my oil yesterday and decided to check the can. Despite being after the PCV, the catch can is really catching a lot of oil and moisture https://photos.app.goo.gl/7ZDvAERecWUGAamTA. It's absolutely full, maybe even to the point of no longer functioning.

So after I dumped it, I decided to see if it was having any effect. Low and behold, I have no more spark knock. Had a tank full of 87 and did about half a dozen WOT runs in 1st and 2nd gear...nothing. At first I thought maybe it had to do with the engine not being quite up to operating temperature, so I waiting until it reached temp and tested several more times. Still no knock. I can't say for sure that the removal of the oil/moisture from the intake charge is responsible, but I haven't changed anything else on the truck. The spark knock wasn't due to poor gas either, because I've had the issue for years and verified it on all different fuel grades from many different sources of fuel.

 

What brand catch can did you install? How did you mount it?

 

Amazon cheapie: https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

I also ordered a section of 3/8 hose so I didn't have to trust the cheap hose that comes with it, and to ensure I had enough length https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

I mounted it to the drivers side firewall. It's not great from an access point, and probably wouldn't recommend it, but I didn't want to have it in the way when servicing the truck.

 

I thought about creating a mount like the new trucks have.

 

Probably NOT having the engine burn that oil keeps the chambers/valves cleaner...... so, not as prone to hotspots that promote pre-ignition.

 

That's my guess, and the reason I did the can to begin with.

The way I saw it, the most common issue with these trucks is the failed plenum gasket which allows the intake to suck in oil and burn it. Common to have spark knock issues with the bad plenum, along with poor economy and other symptoms. Well, if oil coming in through a failed gasket causes those problems, then oil coming in through the pcv system can cause them just as well. I know the PCV valve is supposed to prevent liquid oil from transferring to the intake but at least on a high mileage engine like mine, I'm seeing a lot of liquid transfer to the intake...or at least I was before installing the can.

 

I've had a handful of new PCV valves on my truck and they all let oil through. Not too long after changing my intake manifold gasket I took back off to install an Airgap manifold and there was a nice wet spot on the inside of the old one where the PCV hose hooks up.

 

I installed a cheapo catch can also mainly to keep the oil out of my intake. I made a bracket and mounted mine on the passenger side inner fender. What has me a bit worried is that it seems like there's a lot more vacuum pulling through the pcv valve now. It sucks so hard the valve actually makes a squealing sound. I tried a new valve and it does the same thing. Did you have a similar issue?

 

So long as it's a mopar PCV valve, it will have the correct flow rate. (get one at the dealer, last I check, they were less than 10 bucks.)

 

No, I didn't have this issue, and it looks like we have the same catch can. I did however discover that the catch can will leak vacuum if the cup isn't screwed on real tight, so if you ever start having the "wild vents" check the can first.