Need some opinions on WOT noise

[David H]

Hello everyone,

I've had a 2014 Shelby for nearly two weeks now, and the car is immaculate and perfect, save for one little issue that I can't identify.

At full throttle in third gear, starting from 60-70 all the way through until 110, there is a noise loud enough to be heard in the cabin above the supercharger and exhaust that sounds exactly like how driving through gravel or sand would at low speeds. Little ticks and pings, like small gravel being pulled from the tires and hitting the inside of the wheel wells. It doesn't sound metallic and is not rhythmic.

The moment I pull throttle off, it goes away completely. I have yet to determine if it's at least coming from the front of back half of the car--I just registered the noise today, though I believe I remember it being there prior.

I will test and edit this post after work, and will be trying 4th to see if it gives the same results. 1st and 2nd full throttle is somewhat difficult, as you can understand, but the sound is not present in 1st at 4.5-5k RPM, at least.

Obviously I know this is very limited information, so if anyone has questions I'd be happy to try and give more specific details on request; your opinions and thoughts are appreciated!

 

[Ablaze]

Is your exhaust stock? More specifically do you have an off-road mid pipe?

 

[gimmie11s]

Stop doing it until you find out.

Sounds like detonation and it can kill your $20k long block.

Is this car stock or modified?

Need mod list and moRe detail.

 

[merkyworks]

^This +1

 

[David H]

Is your exhaust stock? More specifically do you have an off-road mid pipe?

Stop doing it until you find out.

Sounds like detonation and it can kill your $20k long block.

Is this car stock or modified?

Need mod list and moRe detail.

Completely stock, 15k miles, running on 91 ethanol free. No codes displayed. I drove it off a Ford dealership not even two weeks ago.

 

[merkyworks]

Maybe the gas you have is bad and not 91 octane. I would run through your current tank and then fill up at a name brand gas station (Shell or Chevron) and see if you still does this.

Assuming this is in fact detonation/knock.
Your car has knock sensors and runs closed loop all the time (even at WOT), so in theory the PCM would keep pulling timing until the knock sensors stop happy. The car might feel like a turd on the hit but the PCM is trying save the motor. The fact the detonation/knock is so bad the PCM can't stop it is really bad and leads me to believe is something big like bad fuel, clogged cat, bad O2 sensor ect.

If it's detonation the more load you put on the engine the worse it gets, 1st-2nd may not do it cause the load is lower but if its detonates in 3rd then you can bet its going to detonate in 4th.

Do you know for a fact the car is 100% stock, maybe someone modded it and then returned it back to stock but messed up on re-flashing the PCM back to stock.

 

[David H]

Maybe the gas you have is bad and not 91 octane. I would run through your current tank and then fill up at a name brand gas station (Shell or Chevron) and see if you still does this.

Assuming this is in fact detonation/knock.
Your car has knock sensors and runs closed loop all the time (even at WOT), so in theory the PCM would keep pulling timing until the knock sensors stop happy. The car might feel like a turd on the hit but the PCM is trying save the motor. The fact the detonation/knock is so bad the PCM can't stop it is really bad and leads me to believe is something big like bad fuel, clogged cat, bad O2 sensor ect.

If it's detonation the more load you put on the engine the worse it gets, 1st-2nd may not do it cause the load is lower but if its detonates in 3rd then you can bet its going to detonate in 4th.

Do you know for a fact the car is 100% stock, maybe someone modded it and then returned it back to stock but messed up on re-flashing the PCM back to stock.

Aside from visual inspection and the dealership's word (not that I would take it as fact), there's no way for me to know if it was modified before I took ownership of it. It's all stock visible under the hood and out the back, but I can't speak for internal components. I have an ODB2 DTC reader/flasher, though I'm not sure if the firmware will be compatible with the newer vehicle (ran fine on my '07).

I ran my traded-in '07 GT with a number of aftermarket parts and a 91 tune on the same gas from the same station that I'm getting for the Shelby, and never experienced any issues from it. Could just be a bad shipment, so I'll run down to a local Shell station and get something I know is good.

I'll also try a gentle test in 4th this evening and get back to you. I know it will sound different on every vehicle because of the circumstances of the detonation, but this really doesn't audibly sound like it. Imagine taking sticky tires and going over a light dusting of 1mm gravel at 10mph or so; just very very light ticking. Not a clunking or knocking, or that it has a lot of force behind it. The engine also is not pulling any power, as far as I can tell, and still rolls through 3rd in three seconds or so.

 

[Coosawjack]

Did the previous owner gut the cats??

If so they can ring like a bell on hard acceleration!!

 

[David H]

Maybe the gas you have is bad and not 91 octane. I would run through your current tank and then fill up at a name brand gas station (Shell or Chevron) and see if you still does this.

Assuming this is in fact detonation/knock.
Your car has knock sensors and runs closed loop all the time (even at WOT), so in theory the PCM would keep pulling timing until the knock sensors stop happy. The car might feel like a turd on the hit but the PCM is trying save the motor. The fact the detonation/knock is so bad the PCM can't stop it is really bad and leads me to believe is something big like bad fuel, clogged cat, bad O2 sensor ect.

If it's detonation the more load you put on the engine the worse it gets, 1st-2nd may not do it cause the load is lower but if its detonates in 3rd then you can bet its going to detonate in 4th.

Do you know for a fact the car is 100% stock, maybe someone modded it and then returned it back to stock but messed up on re-flashing the PCM back to stock.

So WOT in 4th, 5th and 6th don't produce the sound. It also seems like it's coming from within the dash/cabin rather than something being transferred through the frame. I managed to take a recording of a 3rd 70-90mph pull, as well as a few second WOT in 6th for comparison.

In the video below the 3rd gear pull is from 9-12 seconds. 6th gear pull is from 52-56 seconds. The sound is that tinkling little rattle (in the video it sounds a little more like tin foil being manipulated, actually listening to it is a bit more staccato) during the 3rd gear pull. The sound really feels like it's coming from within the dash area.

SLIGHT VOLUME WARNING

 

[MG0h3]

Always hard to say over video but that could be detonation


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[David H]

Always hard to say over video but that could be detonation


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But would it be that irregular and 'light' sounding? I've been trying to just look through examples of engine knock/detonation, and I have yet to come across anything else that sounds like what I have. Engine sounds fine at idle and when not under load, up all the way through the RPM range. I would like to test 5k+ in 4th but the 2014's gearing makes that a little difficult...

 

[biminiLX]

Hard to hear in vid but def don't do 6th WOT at 75 on the stock 3.31 gears.
Schedule a test drive with dealer mechanic where you just bought it?
-J

 

[David H]

Hard to hear in vid but def don't do 6th WOT at 75 on the stock 3.31 gears.
Schedule a test drive with dealer mechanic where you just bought it?
-J

I can hear it clearly in the video, but maybe it's just because I know what it is. There's no detonation during the 6th gear WOT, which is why I included it for a comparison. The sound I'm referring to is between 9-12 seconds in the video; the little 'gravely' sound you hear just behind the S/C whine. The jingle at 12 seconds is just the keys when I pull off the throttle, but the 'crackling' sound is very audible (mostly in left ear for stereo). It just doesn't sound like any detonation I've ever heard. The dealership would be my first contact, if they weren't 3.5 hours away. I could probably get a local dealership to honor the warranty, though...

Additionally, call me a fool but why would it be a bad idea to open the throttle in 6th with the stock final drive gearing? Legitimately curious.

 

[biminiLX]

Some guys had a sticker on the CF driveshaft that would make a noise.
Still I can only hear something for a second or two now that you pointed out the 9-12 sec mark.
Have a trusted Mustang shop close by?
Last, WOT in 6th at 75mph is a bad idea because it's a low rpm to do WOT with the gears Ford neutered these cars with.
What rpm are you at in 6th at 75?
-J

 

[Revvv]

I would also look for stress marks on the carbon fiber drive shaft. Carbon is tough, but not indestructible.

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[raustin0017]

Sounds to me like the vibration noise made by the rear seat belt restraint attachment point....a very common problem. Mine is coming from the right rear seat belt. Take out the lower rear seat, lower the left/right seat backs, and then listen for the noise again. It did not sound like engine noise to me.
Good luck

 

[David H]

Some guys had a sticker on the CF driveshaft that would make a noise.
Still I can only hear something for a second or two now that you pointed out the 9-12 sec mark.
Have a trusted Mustang shop close by?
Last, WOT in 6th at 75mph is a bad idea because it's a low rpm to do WOT with the gears Ford neutered these cars with.
What rpm are you at in 6th at 75?
-J

The sound is only present while I'm on the accelerator in 3rd, and I don't hold it for long. Did some more testing just this morning; 3rd gear 2-3k RPM WOT doesn't make the noise, so it's only at 4k+. But then again, I ran 1st all the way up to 5k just now (slowly, without much load) and didn't hear anything from it, either. So I believe it's specifically 3rd gear 4k+ at high loads, which sounds to me like more of a vibration noise from a loose cabin component rather than engine det. As for 6th, I'm only at 1.5k RPM at 75mph. I wanted to test on an abnormally high load and see if there was any noise, which there wasn't.

Sounds to me like the vibration noise made by the rear seat belt restraint attachment point....a very common problem. Mine is coming from the right rear seat belt. Take out the lower rear seat, lower the left/right seat backs, and then listen for the noise again. It did not sound like engine noise to me.
Good luck

I'll check that out, that sounds more like what it is to me than engine detonation. Thanks for the tip!

 

[MastaAce03]

You need to get a SCT tuning device and data log your car to rule out detonation. You’re playing a potentially very expensive game right now assuming it’s not detonation. Err on the side of caution.

If the car is stock, car needs a tune and couple bolt ons anyway. So don’t feel too bad about purchasing the tuner lol


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[David H]

You need to get a SCT tuning device and data log your car to rule out detonation. You’re playing a potentially very expensive game right now assuming it’s not detonation. Err on the side of caution.

If the car is stock, car needs a tune and couple bolt ons anyway. So don’t feel too bad about purchasing the tuner lol


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I have an old (2011) flash tuner, and trying it today made me realize I just need a new one. I have a new model on the way with tunes, so I'll see what the better data logging on it can tell me. Also seeing if I can use a local dealership and still have my extended warranty honored.