What is this grinding noise when accelerating?

Posted by: VP71

What is this grinding noise when accelerating? - 04/09/21 09:58 AM

Hi panther people,

I've been looking around for an answer to this question, and while there are a few similar threads on here, nothing I've read sheds any light on this issue. I recently bought a 2008 CVPI, which had 123,702 miles on it at the time of purchase. She's now got 124,050. Overall the car appears to be in very good shape, new(ish) intake manifold and valve covers, etc. Aside from some intermittent odometer issues, the one thing I can't figure out is this noise that happens with harder acceleration.

The noise sounds like a grinding type sound, but I can't figure out where it's coming from. My first thought was the belt, which had some unusual wear on the top, almost like someone installed it backwards before putting it on the right way. I replaced the belt yesterday, and before putting the new one on, I handspun everything to make sure the noise wasn't coming from there.

I noticed that there's no noise with smooth steady pressure on the accelerator. However, stepping on the accelerator with a little gusto (i.e. getting up to speed to merge onto a highway) triggers the noise. The noise stops as soon as I let off the gas. I noticed it merging onto a highway and even on the street when stepping on the gas. Not sure if it only happens in certain gears or rev range, but noticed it yesterday between first and second gear around 1,500 rpm. The noise does not happen when the car is revved while in park or neutral, which leads me to suspect this might be a transmission issue?

Going to try to get some audio/video of the sound. Until then does anyone have any thoughts on what this might be?

Much obliged.
Posted by: 2011LX

Re: What is this grinding noise when accelerating? - 04/09/21 10:10 AM

Check the condition of the motor and trans mounts, as well as the exhaust system.

Worn or broken mounts might be causing the exhaust to bind or make contact with something else. They are easy to check: with the hood open, brake torque the engine and see if it moves around excessively.

Rotted exhaust piping, broken hangers, etc, may do the same. A good visual inspection and shake down will reveal any problems.
Posted by: VP71

Re: What is this grinding noise when accelerating? - 04/09/21 10:44 AM

Thank you! Really appreciate the input!
Posted by: RF_Overlord

Re: What is this grinding noise when accelerating? - 04/09/21 04:04 PM

Agree w/2011LX. One question: is this just an audible noise or is there any physical vibration?
Posted by: VP71

Re: What is this grinding noise when accelerating? - 04/11/21 06:30 PM

That's a good question. Honestly, it's hard to tell since the noise happens under acceleration. I can say for sure that there doesn't seem to be a noticeable vibration, but that's not to say that there isn't one I'm just not feeling.
Posted by: TheShadow

Re: What is this grinding noise when accelerating? - 04/11/21 10:55 PM

Did you check the belt tensioner for play when you did the pulleys-spin? How about with the a/c cycling on and off?

Otherwise, an audio would be priceless...
Posted by: VP71

Re: What is this grinding noise when accelerating? - 04/12/21 12:07 PM

Yes sir, I did check the belt tensioner for play and it was solid. There doesn't seem to be an issue with the a/c being on or off, the noise is present with both. I'm going to try to get some audio soon.
Posted by: TheCableGuy

Re: What is this grinding noise when accelerating? - 04/12/21 01:47 PM

I’m wondering maybe a pulley/bearing going out.. my work truck, yes different but I had a very odd groan noise when my truck would get around 2500-3500 rpms. (2013 F150). Water pump detonated about a month later. Turns out it was that.. and get this, would only do it while actually driving. I reved it multiple times to 4000 rpms while in park without being able to recreate it.

Could be a handful of things. Idler pulley, PS pulley etc etc.. just my thoughts.

I know you said it doesn’t happen in idle which I find is very odd. Could he that intermittent maybe.
Posted by: VP71

Re: What is this grinding noise when accelerating? - 04/12/21 04:20 PM

I want to apologize in advance, this is terrible audio. There's too much ambient noise outside right now to get this better quality. That said, around 7-8 seconds into the vid, if you listen closely you can hear the noise. Again, I'm sorry for the bad quality.

https://youtu.be/8RmKIJZtfUA
Posted by: professorP7B

Re: What is this grinding noise when accelerating? - 04/12/21 07:44 PM

Right at about 8 seconds...sounds like an ABS activation....
Posted by: RF_Overlord

Re: What is this grinding noise when accelerating? - 04/13/21 01:44 AM

All I hear is a thump.
Posted by: VP71

Re: What is this grinding noise when accelerating? - 04/13/21 11:04 AM

Yeah, again, I'm sorry for the bad audio. I tried to record yesterday afternoon. Where I live between 2:30 p.m. and 7:30 p.m. the amount of traffic around here is insane. Between the noise from the other cars, and not being able to accelerate to where this noise is present is hard. I'll probably have to wait for the weekend to record a better video. Thank you nonetheless for taking the time to listen. I really appreciate your's and everyone else's help with this.
Posted by: GM_Guy

Re: What is this grinding noise when accelerating? - 04/15/21 07:37 PM

Can't really tell, but heres an experiment, drive with OD locked out (including the freeway portion) and see if the noise is still present under the conditions it usually might occur.
Posted by: GMUE03

Re: What is this grinding noise when accelerating? - 04/16/21 05:25 PM

Could be spark knock, have you tried cleaning your MAF sensor?

(Quick example of what spark knock sounds like)
https://youtu.be/6xTWHJADFe8
Posted by: VP71

Re: What is this grinding noise when accelerating? - 04/20/21 12:36 PM

Thank you for the tip! I'll give this a try. If it is or isn't present what would that indicate?
Posted by: VP71

Re: What is this grinding noise when accelerating? - 04/20/21 12:37 PM

Haven't cleaned the MAF. The guy I bought it from said he cleaned it before selling it. Should've been a case of trust but verify. I will check that out. Did just replace the air filter this weekend.
Posted by: RF_Overlord

Re: What is this grinding noise when accelerating? - 04/20/21 01:26 PM

Originally Posted By VP71
The guy I bought it from said he cleaned it before selling it.
Hopefully he used either MAF cleaner or electrical contact cleaner. If he used carb cleaner then it's possible it's damaged now.
Posted by: Tenevic_P71

Re: What is this grinding noise when accelerating? - 04/20/21 06:03 PM

The noise at 7-8s in your video sounds distinctly like the *clunk* of a bad drivetrain mount. If you lock the car in 1st or 2nd and alternate between stepping on and letting off the gas I bet you can get it to clunk repeatedly.
Inspect engine/transmission mounts. If you don't find anything there I would look closely at transmission tailshaft, driveshaft u-joints, rear suspension/axles. Sounds like something somewhere has excess play.
Does not sound at all like spark knock to me.
Posted by: VP71

Re: What is this grinding noise when accelerating? - 04/21/21 06:47 AM

Thank you for the input! This is something I'm adding to the checklist. Appreciate your thoughts!
Posted by: VP71

Re: What is this grinding noise when accelerating? - 04/21/21 03:49 PM

Alright guys, slightly better audio quality. Could only grab a few seconds' worth, didn't want to be screwing around with my phone in my hand while trying to rapidly accelerate on public roads.

https://youtu.be/RxGNesa2K9c
Posted by: Tenevic_P71

Re: What is this grinding noise when accelerating? - 04/21/21 09:44 PM

That video is much more clear.
Take the accessory belt off and (briefly)do the same thing you did in the vid and see if the noise is still there. You can also see if the noise is present if you brake torque it while stopped.
Posted by: VP71

Re: What is this grinding noise when accelerating? - 04/22/21 09:14 AM

I'm a little hesitant to run the engine without the belt for two reasons. First, the obvious issue of running the engine without the belt. While running it for a few minutes shouldn't be an issue, the other reason I'm hesitant is that the noise isn't present when the engine is revved while in park or neutral. That being the case, it makes me worry about the cost-benefit of that test. Not ruling it out, just being overly cautious. Let me know what you think?
Posted by: bspurloc

Re: What is this grinding noise when accelerating? - 04/22/21 01:18 PM

you arent going to do anything to the engine with the belt off drive down road and back... you will be running on battery though, so do it and come back or the car will stall as the battery dies... have lights off radio off etc etc everything off

Now I cant really hear anything in the video's u need to say the exact seconds in the video and say exactly what u did at that time.
The one thing you cant test sitting in park is the kick back of the PI alternator pulley.
If you punch it causing the engine rpm it instantly exceed the belts speed the alternator pulley is built to allow back spin so the belt can catch up instead of causing it to slip and squeal as it catches up.
I may be explaining this wrong, so dont waste our time telling me how im explaining it wrong just stick to the fact of the alternator pulley has this feature and that may be the cause of the noise.
Posted by: RF_Overlord

Re: What is this grinding noise when accelerating? - 04/22/21 01:29 PM

I can hear it better in the second video, but it's still kinda iffy due to background drone. Does it only do it on throttle tip-in or is it constant while you're accelerating? It sort of sounds like a catalytic converter rattle...

I don't think we're gonna solve the problem here, though. It's going to need a competent mechanic to listen to it in person.
Posted by: VP71

Re: What is this grinding noise when accelerating? - 04/22/21 02:06 PM

Very interesting. I didn't know the PI alternator did that.
Posted by: VP71

Re: What is this grinding noise when accelerating? - 04/22/21 02:10 PM

Appreciate you taking another listen. The noise happens when I give the gas pedal a hearty push as I did for this video. It'll also occur on the highway sometimes with normal acceleration. Oddly enough, when I press the gas at lower speed to get the noise, like in the video, the noise goes away once I let up off the gas, whereas on the highway it goes away with more acceleration.

Appreciate all the input guys. Gonna have to add this to the list for the mechanic.
Posted by: Tenevic_P71

Re: What is this grinding noise when accelerating? - 04/22/21 03:02 PM

I definitely hear the knock/rattle clearly in the 2nd vid. Another thing I would consider checking are the torque converter/flexplate bolts to see if they're loose and ensure they're all torqued correctly. Could also be exhaust as stated above. Maybe a loose flange or something.
However I agree with RF_Overlord; to diag this it is going to take a thorough inspection from someone with experience and knowledge on the subject. I'm not sure if you're a mechanic.
Posted by: bspurloc

Re: What is this grinding noise when accelerating? - 04/22/21 11:37 PM

Ok yeah that wouldnt be the alternator.
on a civilian crown vic assuming engine is in good shape, if u gently get onto the on ramp and then put it to the floor and keep it there as the transmissions shifts I think its the 2-3 shift the belt will squeal right as 3 engages. so the PI alternator has a different pulley that allows for slight back spin eliminating that belt squeal.

So anyway yeah, this isnt an easy one.
Do u not hear anything going D to R a few times no clunk?

Originally Posted By VP71
Appreciate you taking another listen. The noise happens when I give the gas pedal a hearty push as I did for this video. It'll also occur on the highway sometimes with normal acceleration. Oddly enough, when I press the gas at lower speed to get the noise, like in the video, the noise goes away once I let up off the gas, whereas on the highway it goes away with more acceleration.

Appreciate all the input guys. Gonna have to add this to the list for the mechanic.