Back again with a new Issue, Spark Knock??.... any Help?

[Rdizz]

So as of maybe a few days or possibly longer since it is now "jeep season" Took my doors off and I am hearing a rattleish noise that comes when i am at low RPM soft accelleration. To me it sounds like possible Spark Knock. It is hard to describe... Picture a metal ball inside of a wooden container and inside that container are mass amounts of ridges and this ball travels across them making a sound at every ridge which are placed back to back. Make sense?

I checked my Fuses, the PCV for oil seepage (didnt see any) replaced my air filter and installed a catch can (just incase) Could this just be a case of "bad gas"? Should I run it out and throw in some premium from a top tier station? or is this just a myth and as we all know the 3.6 isn't designed for higher octane so I feel like that is just a band aid on a much larger issue. I also went underneath and didnt see anything lose that could cause this sound.

any thoughts or advice on this? 2020 Jeep Glad 3.6 with 24k miles

Found this video (not mine) it sounds very similar to this.

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[JTGuy]

I use nothing but 91 octane and have never had an issue. I know it costs more and some say the 3.6 is designed for regular.

 

[Hootbro]

My guess is either the electric vacuum pump or a belt/pulley squeak if it is anything like that video you posted.

 

[intentsrig]

I had this issue all the time with my manual JL. The only thing that helped was running 91.

 

[jav_eee]

the engine is designed for 87 but it is "high compression". Won't cost a whole lot for you to try a higher octane and see if that helps. FWIW I only use 89 or 93 and don't have any issues.

 

[Banned]

All I heard was an engine running. Take it out and beat the piss out of it. That's what it likes.

 

[ShadowsPapa]

I run only 87 octane.
Yes, these are in theory "high compression" engines but that's the mathematical number, not the dynamic real compression because in low lift mode, the cylinders are not completely filled, thus you won't have the highest possible combustion pressures.
Anyone who understands cam timing, profiles, valve lift and so on will tell you - these won't be operating at maximum compression at lower RPMs

If this is a manual transmission, check the threads on "rattling" associated with those - spoiler alert - in those cases, it's not the engine.
Also - if it's a stick, rev it up higher and stop trying to keep the RPM low.
Too many believe modern engines must be run slow to run best.

 

[ShadowsPapa]

I use nothing but 91 octane and have never had an issue. I know it costs more and some say the 3.6 is designed for regular.

It is designed for "regular". Watch the timing on these things while driving it, and at RPM below about 2800, you are in low lift mode, and so on, and won't even come close to the theoretical or mathematical "11.3:1" compression ratio.
That's assuming you have a full cylinder with piston at BDC and the valves are fully closed before the piston starts moving up.
That's not the case in reality. Low lift intake means the cylinder isn't fully filled, and late valve closing can release some of that "air" as the piston starts moving up.
That compression ratio scares people. It shouldn't.
Valve lift, timing, ignition timing, EGR controlling the charge temperature, and more, combine to keep detonation to a minimum at best, if any at all.
Never had it in any 3.6 we've ever owned and we always run the cheapest stuff we can find, although shoot for top quality fuel - and "premium" != "quality" fuel.

 

[JW Jeep]

There is a Mopar technical service bulletin on something of this sort NUMBER: 09-012-22 Spark knock from carbon build up And possible bad pcv valve causing this ? With 24,000 miles I doubt it would be this ? I’m running 85 octane at higher elevation and have no problems ? Does it do it at hard acceleration too ? Maybe try some sea foam ? I have had some good luck with this on other vehicles ? There is a lot of things it could be however ? Bad gas is one of them ? Belt tensioner also ?​

 

[jav_eee]

Watch the timing on these things while driving it, and at RPM below about 2800

I do, and i see +30 degrees a lot. I also use higher than 87 octane. What would i be seeing with 87? Do you monitor timing?

 

[ShadowsPapa]

I do, and i see +30 degrees a lot. I also use higher than 87 octane. What would i be seeing with 87? Do you monitor timing?

That's the highest you see?
I've not watched the highs, but have seen as slow as 2 degrees ATDC.
Some of us run 36-38 degrees on engines from 50 years ago, so 30 is nothing.

It's more than that compression number and timing.
I wish people would ignore the compression ratio.
That's, like I said, a number comparing volume of a chamber with the piston at the bottom vs. volume of a chamber with the piston at the top. You will be running much lower pressures on these at lower RPM and lower valve lift, and depending on the valve timing at a given time (retarded intake timing), you'll bleed off enough air to end up with more like 9 to 1.

I don't know what the quench is like on these, but with tight quench, and good swirl of the intake air, quick burn chamber designs, you can run pretty high compression what we old farts call "pump gas" - meaning ordinary cheap 87 and keep the timing up there.
There's no reason in the world to have to run anything other than 87 unless you have a problem engine.

30 degrees - That's slow timing, IMO - at least compared to engines of the past, V8s, even the lowly little 4.0 had "faster timing. My 377 HP 360 with comp cam and so on runs at least 36 degrees (and I've run anything from 87 to 91 depending on my mood)

You want the spark to occur at such a time to cause the maximum chamber pressure to be reached at 14-16 degrees ATDC for maximum HP and efficiency.
For many legacy V8s, that means timing in the 36-38 range "all in" - meaning vacuum and mechanical advance plus base timing.
I'll have to watch to see what my higher timing numbers on the JT are when I get to where I get things hooked up again.

 

[Rdizz]

I run only 87 octane.
Yes, these are in theory "high compression" engines but that's the mathematical number, not the dynamic real compression because in low lift mode, the cylinders are not completely filled, thus you won't have the highest possible combustion pressures.
Anyone who understands cam timing, profiles, valve lift and so on will tell you - these won't be operating at maximum compression at lower RPMs

If this is a manual transmission, check the threads on "rattling" associated with those - spoiler alert - in those cases, it's not the engine.
Also - if it's a stick, rev it up higher and stop trying to keep the RPM low.
Too many believe modern engines must be run slow to run best.

It is an automatic. I did wind up putting premium in it and the sound has for the most part gone away... So i dont know.

 

[starrskream]

I’ve had a metal rattling sound on a Ford ranger and my Xterra. In both cases, it turned out to be welds on a heat shield. They were broken, and rattling.

 

[ShadowsPapa]

I’ve had a metal rattling sound on a Ford ranger and my Xterra. In both cases, it turned out to be welds on a heat shield. They were broken, and rattling.

Several members here have posted over the years about a similar cause - a shield, or in the case of the manual transmissions, it seems to be related to the clutch pedal in some way.
Seriously, unless there's an issue with oil consumption, faulty PCV or really very uncommon carbon build up, or a sensor issue and so on, there should be no true detonation from these.
If "premium" "fixes it" then something needs to be investigated. Again, many millions of these on the road in Jeeps of all flavors, Ram trucks, Charger and more - and no such issues.
This PUG has been around in Jeeps and other FCA vehicles since 2016. It's now 2024. That's 8 years and how many millions of these things all running on 87.
Those that "rattle" - there's a problem. Find and fix it. It could even be an EGR-related issue.
If mine started with a TRUE detonation "rattle", I'd know, and be looking for a cause, not tossing more expensive fuel at it. 91 around here is crazy expensive compared to 87.
I'd be sitting at the table with the service manager having some technical discussions - he'd not be able to push me off as just some unknowing customer. I'd be throwing numbers and science at them.

 

[zprovo]

My 2022 Mojave has had an itermittent spark knock from new. Very short duration until recently. Over the past month (doors off, so it could have been happening a bit longer) the spark knock duration has gotten longer, always hot, always a slow accelleration often during an upshift (automatic). Yesterday I could feel a power drop while going uphill which stopped the knock. Am I correct in assuming the engine sensed the knock and reduced power? It didn't throw a code.
I'm trying to gather as much information as possible and/or fix myself because the dealer will say this is normal.

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