Odd Engine Noise

[SelfmodJT]

Just to give people a heads up, so in other threads it seems like a similar noise is pre ignition or detonation? Anyways, I just realized the gas I have been using is basically low tier gas. I used giant gas for the savings and speedway gas. Both those gases aren't good.... so I put in Mobil and the noise is barely noticeable. I'm hoping the noise was a gas issue because I still had about 1/4 of a tank of the low tier gas. I'm going to let my tank almost go to empty before refueling next time. I'm pretty sure 87 octane from giant vs Mobil is different lol.

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[Mojave Gladiator]

My manual does this when I don’t Rev the RPM’s up high enough before shifting. It sounds similar to “dieseling”… the 3.6 simply doesn’t make good usable torque under 2200K.

 

[SelfmodJT]

My manual does this when I don’t Rev the RPM’s up high enough before shifting. It sounds similar to “dieseling”… the 3.6 simply doesn’t make good usable torque under 2200K.

I have a manual too, that's what I presumed too but the top tier gas does seem to make a difference. Seems to purr a lot better too. Looks like I'll have to make sure I always put in top tier gas from now on.

 

[saltlife4shore]

I use 91 octane fuel, still have the noise.

 

[SelfmodJT]

Regardless of octane, I think top tier gas makes a difference. No?

 

[Higher_Ground]

I think I'm getting this too, but it's hard to tell.

I drive through neighborhoods with an excessive amount of speed bumps... and I notice it most often right after the rear wheels come over the hump and I start to accelerate (usually it's in 2nd on the automatic). I hear about 0.5-1.0 of rattling and had up until now just assumed it was from the speed bump itself. But after listening to these videos and the fact it seems to only happen when accelerating after a relatively quick deceleration has me worried it's something else.

 

[iGlad]

I use 91 octane fuel, still have the noise.

Same here. I am also regeared to 5.13s and its still occurring.

 

[LoJac963]

Regardless of octane, I think top tier gas makes a difference. No?

Correct, most everyone including myself have tried all tiers of fuel with no resolution. There is something else with the engine/tranny. I am curious if larger tires is what is causing this. I didn't seem to have the issue on stock 33s. I don't know if a regear will fix the noise but I don't want to spend a few thousand honestly to fix the noise with a regear and it doesn't fix it.

 

[j.o.y.ride]

Chevron 91 solves a lot of weird engine knock type noises for me. BP 91 makes them come back. Maybe in my head, but it just gets really set in it's way, top tier or not.

 

[Fortus]

From the manual:

"While operating on gasoline with the required octane number, hearing a light knocking sound from the engine is not a cause for concern. However, if the engine is heard making a heavy knocking sound, see an authorized dealer immediately."

 

[ShadowsPapa]

Automatics generally will downshift and avoid lugging, apparently people driving the manual version of the JT just aren't used to winding engines up enough and tend to keep the RPMs down instead if downshifting and getting the engine away from 1600-2000 RPM under a load.
I can't stand engines running 1600 RPM - I'm used to 3,000-3,200 RPM on the highway with some of the cars I've had (and still have)

I run my little 4.0 up 3,000 -3500 rpm before shifting and never lug it or load it up at anything under 2,000 RPM before shifting. 2,000 RPM and below is for cruising on level roads, anything else and I downshift my car. I never hit 5th with that T5 until I'm over 60 mph.

Maybe that's one reason I've not heard any pinging at all with my JT - I don't let it work hard under 2,000 RPM - I push harder and force a downshift.

 

[jmdwifi]

From the manual:

"While operating on gasoline with the required octane number, hearing a light knocking sound from the engine is not a cause for concern. However, if the engine is heard making a heavy knocking sound, see an authorized dealer immediately."

This is bullshit. Cant be good for and engine to have the pistons beating on the cylinder walls at the wrong time. It's bad enough it rattles when you start it until it get oil pressure. I don't know how this will turn out long term. I'm ready to buy an old truck with a simple engine.

 

[ShadowsPapa]

This is bullshit. Cant be good for and engine to have the pistons beating on the cylinder walls at the wrong time. It's bad enough it rattles when you start it until it get oil pressure. I don't know how this will turn out long term. I'm ready to buy an old truck with a simple engine.

I've worked on cars since I was about 14 - it's talking about brief light ping. And it's correct. I've worked on engines that have had a history of light ping - and you don't see damage.
There's a fine line, though..............
My fear is that people today won't know the difference between what's ok and what's not ok.
It's not about the pistons beating on the cylinder walls at the wrong time - it's the sonic boom from colliding flame fronts. Yes, there's excess pressure but it's more on the head of the piston (I have proof in pictures of the results), and yes if severe it blows away the boundary layer exposing the top of the piston directly to extreme temperatures.

 

[SelfmodJT]

This is bullshit. Cant be good for and engine to have the pistons beating on the cylinder walls at the wrong time. It's bad enough it rattles when you start it until it get oil pressure. I don't know how this will turn out long term. I'm ready to buy an old truck with a simple engine.

If your dealer says it's normal, just have it noted on the worksheet that they heard it detonate and told you it's normal so it's on record. Your warranty for the engine is 60k miles or 5yrs, just drive the shit out of it and keep using 87. If it's not normal, theres no way itll go 60k and stay intermittent. If it's a constant rattling for secs at a time and clearly audible they have to address it. If youre close to 60k and it's still intermittent then perhaps it's not doing anything to the engine. Either sell it or buy an extended warranty for peace of mind. You're gonna drive yourself crazy if you keep let it bothering you everytime you drive. It's not something you cant control so fuk it, turn up the radio.

 

[81Mojave]

That’s the most Jeep thing I’ve read all night!!?

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