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My son is an hour away and we are trying to diagnose this problem on a 2001 Toyota Corolla. When the car is accelerated slowly and gradually everything is fine. However when the gas "pedal is to the metal" he hears a grinding sound under the hood. I suspect from prior experience that it is the radiator fan shroud touching the radiator fan blades. I am not sure what causes a loose fan shroud to go out of position only on hard accelerations, but I suspect and fear that it could be motor mount related.

Have any of you encountered anything similar? I also hope it is not transmission related.

  • A front wheel drive vehicle has electric fans. Hard acceleration shouldn't make a difference. Could the noise be pinging? – cano Jul 1 '17 at 0:47
  • Check the engine belts also for any misalignment or damage – Ciril Jul 1 '17 at 6:07
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    I would check the motor mounts for excessive travel. – Moab Jul 2 '17 at 1:27
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    No, it is a grinding sound. Pinging would be a knocking sound. – 0tyranny 0poverty Jul 2 '17 at 2:14
  • @Moab you were right. It was the motor mounts. If shocks are not replaced, the motor mounts will take the brunt of the potholes. – 0tyranny 0poverty Jul 11 '17 at 0:47
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After arriving on the scene, first I established the scope of the problem and areas affected. The noise did not happen if I reved up the engine rpm in park. so we can rule out a valve bearing or other engine problem. It did not happen if I gunned it in reverse, and it did not happen in any forward gear if the car was already in motion. It only happened when hard acceleration form full stop and it went away after the car was going 5mph and faster. If I accelerate very gradually from full stop by only tapping the accelerator, it did not happen.

I asked my son to hold the brake while in drive and step on accelerator while I watched for the engine to rock out of place. Sure enough there was more than an inch of movement of the engine, so I knew it was the motor mounts.

I then asked my son if he hit a deep pot hole or other obstacle at high speed and he admitted he did. Then I asked him if this grinding noise problem was noticed only after striking the pothole and he said yes.

I checked the front end shocks and struts and they are shot.

So, that is the problem when bad shocks are not replaced. The road shocks are absorbed then by the engine mounts, which they are not designed for.

Diagnosis: 2 or more engine mounts were damaged, so the engine is no longer fully secured to the chassis. The most pronounced rocking or movement of the engine occurred when accelerating forward from full stop. Since the vehicle is front wheel drive, the automatic transmission assembly moved out of position slightly as well, not much, but enough for front wheel drive axle components to rub on something and cause said grinding noise. After the car reached some motion forward, the engine and attached rocked back or settled back in place due to gravity and rubbing noise stopped.

Lessons learned: Replace shucks and struts at recommended intervals and avoid pot holes.

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