Chewing metal sound when accelerating

[packmule1911]

This Jeep doesn't make Jeep loving very easy these days.

When I accelerate, rpm's over 2500, I get a lovely higher pitched crunching metal sound/vibration sound directly in front of the driver seat/foot well area. It's in the engine bay, but that's the direction it seems to be coming from.

This does not happen when stopped, only when it's being driven. 2200 rpm's is great, idle is smooth. Imagine a spoon stuck in a garbage disposal, but a little higher pitched, thinner sound, and that's it.

This started yesterday after I filled up with regular gas from my normal place, and put in some Purple Power stuff because the store was out of Seafoam.

Did the CAT fry, or the octane is now whacked? I should have just filled it up and left well enough alone with the stupid additives, but I'm still trying to tune this thing up.

[denverd1]

ouch. flexplate?

There's an inspection cover right where the engine bolts to the trans. remove it and check the condition of things

[NW99XJ]

Well the obvious here is going to be to double check your oil level, but i think its not internal to the engine...
I have a couple of questions that may help narrow down what this may be:

- is the noise dependent on temp (either outside or engine - meaning does it change after the engine warms up or when cold)

- does the noise change when you are braking hard, or turning a corner sharply or something?

- Does the noise only happen under load (meaning at a stop if you rev the engine does it happen then too, or only when accelerating?)
- if the noise can be recreated by grabbing the throttle control when standing over the engine, then see if you can narrow down the location of the noise... is it a component such as the power steering pump, alternator, idler pulley, or water pump?
- if the noise cannot be recreated unless the vehicle is in motion, or under load, then, its going to be a little more difficult to track down.

Having someone to help you thru this procedure is going to be of great benefit, they can press the pedal and you can climb around/over/under the jeep and try to isolate the noise.

Do a visual inspection of everything, CHECK ALL FLUIDS, look at both the engine mounts as well as the tranny mounts. Look for clean metal or metal that has been stripped of any point/shiny/fresh ground metal/etc.. (looking for signs of metal on metal contact here.)

I'm leaning towards bad/broken motor mount, and what your hearing is the fan hitting the core support/radiator.... But it could be other things too... answer the above questions as best (and as detailed) as you can, and we'll go from there.

[packmule1911]

- is the noise dependent on temp (either outside or engine - meaning does it change after the engine warms up or when cold)

Sound occurs at any temp.


- does the noise change when you are braking hard, or turning a corner sharply or something?

Only under load. No noise revving while stationary, or braking.


- Does the noise only happen under load (meaning at a stop if you rev the engine does it happen then too, or only when accelerating?)

Only under load. No noise revving while stationary.


- if the noise can be recreated by grabbing the throttle control when standing over the engine, then see if you can narrow down the location of the noise... is it a component such as the power steering pump, alternator, idler pulley, or water pump?

Will try this, but I haven't been able to get it to make the noise unless I'm moving and step on the gas.


Do a visual inspection of everything, CHECK ALL FLUIDS, look at both the engine mounts as well as the tranny mounts. Look for clean metal or metal that has been stripped of any point/shiny/fresh ground metal/etc.. (looking for signs of metal on metal contact here.)

I'm leaning towards bad/broken motor mount, and what your hearing is the fan hitting the core support/radiator.... But it could be other things too... answer the above questions as best (and as detailed) as you can, and we'll go from there.

I put a power steering pump in recently, and I expect it's garbage, but I will focus on inspecting the mounts. What I imagine seeing when I hear it is a metal plate violently bouncing around on another hunk of metal. When the sound is not going on, it's actually running really smooth right now (except for the occasional and ongoing heat soak problem).

[NW99XJ]

If the power steering pump was bad you would have a couple different symptoms than what you're describing...
First, you would DEFINITELY feel it in the wheel, sluggish, or intermittent feel in the steering. Also the sound would be happening all the time, because as long as the engine is running the power steering pump is also working. So i dont think its that.

The fact that it ONLY happens under load makes me think its something to do with what the engine is doing once the rotational torque force of the engine competes against the resistance of the drivetrain.
The motor (not having anything to fight against other than itself when in neutral) will not move as much as when you have the transmission engaged.
Try this:
If you're an automatic... pull the ebrake, step on the brake pedal, put it in DRIVE and give it some gas, like you were gonna try to do a burnout....
If you have a stick.... pull the ebrake, step on the brake pedal, put it in 1st gear, and give it some gas, like you were trying to do a burnout...

If THIS procedure recreates the noise...then we know its related to the movement of the engine... But that doesnt necessarily mean its the mounts.
I have heard recently... that thru a regular inspection, that someones tranny had several bolts work loose, and that only a couple were actually more than finger tight, or even still there. I have also heard this same thing happening with the transfer case to the tranny.... THIS IS EXTREMELY RARE .... but you cant rule it out.

The flex plate issue is still hanging in the back of my head as a potential culprit as well.... If you haven't already... remove the inspection cover, and take a look at it.... you'll be looking for cracks along by where the mounting holes/bolts are...
Here's a decent video of how to do it... (the guy is holding his camera wrong, but oh well - despite that.... the content is good enough to get you what u need.) https://www.youtube.com/watch?v=k21NSEm96H8

And a halfway decent write-up about the process as well:
http://www.cherokeeforum.com/f51/how-fix-flexplate-knocking-125547/

Good luck... hope this helps... we just got to try a couple more things, and we should have it narrowed down.
Do the above steps.... and report back... we'll go from there.
(also.... if you can.... post up a video of this noise - it might help)

[packmule1911]

Try this:
If you're an automatic... pull the ebrake, step on the brake pedal, put it in DRIVE and give it some gas, like you were gonna try to do a burnout....
If you have a stick.... pull the ebrake, step on the brake pedal, put it in 1st gear, and give it some gas, like you were trying to do a burnout...

Took it by a friends place this morning. I pay 50% of their diagnostic fee, every other time, and he has a guy take a look at what I'm complaining about.

This morning's conclusion on this problem is spark knock. This makes sense since the noise started after a fill up, and a bunch of additive. SO ...... I'll keep filling up, and lay off the super-duper extra-special secret sauce additives and see what happens.

I am going to inspect the flex plate and such though.

Thanks All.

[denverd1]

Took it by a friends place this morning. I pay 50% of their diagnostic fee, every other time, and he has a guy take a look at what I'm complaining about.

This morning's conclusion on this problem is spark knock. This makes sense since the noise started after a fill up, and a bunch of additive. SO ...... I'll keep filling up, and lay off the super-duper extra-special secret sauce additives and see what happens.

I am going to inspect the flex plate and such though.

Thanks All.

Good to hear!

[packmule1911]

Good to hear!

No kidding. Worst spark knock I ever heard of. I've read that most cars have knock when the octane it too low. Mine was the opposite. It's slowly getting better with each fill up of 87, and I've given up the additives.

That Purple super-power stuff must be pretty intense. If they'd had Seafoam in, I would not have had this problem. Learned something, which I welcome, but dang that was a frightening sound.

[NW99XJ]

So are the plugs fouled now? .... i'm curious to see what the electrodes look like after all this.

[packmule1911]

It's not running poorly, and I haven't looked at the plugs. The dealer put new ones in as a step to solve the heat soak problem (before I knew what the cause was), which was back in December.

Is the coil assembly fragile? I saw it removed, but I've not removed it myself.

While on the topic of plugs, what do people here prefer to use?

[abebehrmann]

Is the coil assembly fragile? I saw it removed, but I've not removed it myself.

While on the topic of plugs, what do people here prefer to use?

You'll want to be a little careful with it but it's not too fragile. Have one on the GF's TJ and it was a breeze to remove.

I think everyone here recommends the regular copper Champion plugs. Heard of people having problems with the fancy platinum plugs but mine had some in it when I bought it and it ran just fun.