Strange sound when engine under load

[gizzwell]

Good Day,

My Explorer has been making a strange noise that seems to be coming from the engine bay whenever accelerating in a high gear or when climbing an incline. It's like a rattling sound. I notice that the vehicle does not make this noise whenever the weather is rainy and cold, and that the noise is more frequent during hot and dry days.

At standstill with the shifter in either N or P, the engine sounds good and normal. Revving the engine sounds normal as well, no rattling noise.

When accelerating the car, sometimes as early as 1500rpm up to about 2500rpm, the vehicle produces the noise, then once the transmission shifts to a lower gear and the rpms climb to 3000+, the noise is gone. Also when driving up steep inclines, the rattling noise is present.

Vehicle specs: 2014 Explorer 3.5 v6 Ti-VCT (not ecoboost) with intelligent AWD. 78000kms (~48500miles), all stock

I have taken the Explorer to different mechanics and dealerships, each with their own opinion of what's causing the problem. The vehicle does not produce any CEL or fault codes.

Here is a list of things I've done to the vehicle:
1. Cleaned MAF and Throttle body
2. Changed air filter
3. Changed spark plugs
4. Flushed coolant, replaced thermostat and radiator/overflow cap
5. Flushed/Changed Transmission Fluid, Rear Diff Oil, and Transfer Case oil
6. Changed Engine Oil and Filter

I thought at first that the engine might be pre-igniting but filling with either 91, 95, or 97 octane gasoline does not seem to make a difference with the frequency of the rattling noise.

Here is a video of the sound:

 

[peterk9]

Welcome to the Forum.
Not really sure what it might be. When accelerating and the noise happens does it disappear as soon as you lift off the gas? Do you have the factory tow package? Just wondering if the air intake may be loose.

Peter

 

[gizzwell]

Welcome to the Forum.
Not really sure what it might be. When accelerating and the noise happens does it disappear as soon as you lift off the gas? Do you have the factory tow package? Just wondering if the air intake may be loose.

Peter

Hello thanks for replying. Yes the noise disappears immediately as soon as I lift off the gas. I do have the tow package.

I inspected the airbox and the intake tube to the throttle body, all seems to be fine. I wonder if it could be a vacuum leak somewhere? Although the engine idles and drives nicely except for the rattling noise during acceleration.

I was also able to buy an OBD2 device and played around with it today. I don’t really know which data to pay attention to. Checked the ‘misfires’ panel and it said zero(?) don’t know if accurate or what.

Regards
Gizz

 

[Turdle]

If it sounds like someone is under the hood shaking a can of marbles, it's predetonation knock, try premium higher octane fuel

 

[gizzwell]

Good day,

I think I may have found out what is causing the noise under acceleration.

I removed the upper intake manifold to take a look and found a lot of oily residue just before the intake valves. Looked at the spark plugs and they all look fine, little brown but seems to be about right. Used a borescope to look inside the cylinders and they didn't look too carboned up, the lining showed no wear and good cross hatching.

Since the intake was removed I went ahead and looked at the PCV valve and hose, found a lot of liquid and the PCV valve looked very dirty/clogged. Cleaned it with carb cleaner as well as the hose it attaches to, then buttoned everything up.

Took the SUV for a test drive around the hilliest parts of town, both spirited and relaxed. No more noise!

Still observing if the noise will come back but have already ordered a new PCV valve just incase since they don't cost a lot.

My theory is that under heavy loading and low rpm, the cylinder pressures are at their highest, therefore blow-by gasses are high as well. This works the PCV system a lot and anything wrong with it will show itself. In my case the oil inside the hose was probably gurgling hence the rattling noise. This could also throw the air:fuel mixture off since the PCV is connected to the vacuum lines of the intake manifold, downstream of the MAF sensor.

Of course I could be wrong. But I'm just happy the car works as it should now with no alarming noises when driving. Will update if anything comes up. I'm just sharing this in case someone might encounter a similar problem.

Regards
Gizz