Just noticed a loud squealing sound coming from the engine area before I start the truck, but with the key in the on position. I'll try to get a video the next time it happens. I assume it's something starting/warming up, but it's louder than anything I've ever noticed. It lasts probably 20 seconds.

 

Low pressure fuel pump is what I think you are hearing.


Try again but listen next to the drivers door, underneath the truck and see if that is where the sound is actually coming from.

 

Hmm, ok. I assume it's bad if I'm hearing that...? I haven't gotten any warnings on the dash (yet)

 

Coincidently, after reading this post earlier, I went out and did a headlight and foglight swap for some LED's. When I turned on the key to get the fogs to come on for a check, I too got the squealing. It appears to be the pressure control valve on the fuel rail returning fuel to the tank while the low pressure pump is pressurizing the system for start-up. I was key on - engine off a few times while checking the lights. I got the squealing twice, but it was quiet the other three times I was testing. I don't believe you are hearing things, and I don't believe it is the low pressure pump. When I got the noise, I was already in front of the truck with the hood open. The noise lasted the full priming cycle of the low pressure pump, so I had plenty of time to go listen to it as well.

 

DEF pump? There is something underneath the hood that is always clicking on and off and I hear fluids running through it when I turn it off or just cycle the key.

Only time I heard squealing was when a cat was under the hood and I went to start the truck.

Unless I missed the TSB on it, a squealing pump is not usually a good thing.

 

Dak, mine wasn't the pump squealing. It was the valve on the fuel rail that returns the fuel to the tank. It is on the rail in the valley. The cat will squeal after the engine is started and their tail is caught in the belt. (Been there - done that!) This is happening before starting, and it is not the usual sound of the DEF injector, or the wastegate solenoid, EGR valve, etc.

 

Yeah, it's definitely not a usual sound, and I know these trucks make a lot of them when starting up. Funny that you heard the same thing, I too have not been able to replicate it after a few tries.

 

Just get a cat and put its tail in the belt - then start it up...

Welp, as long as it isn't a pump and is just fluid and a valve probably is no biggie.

 

The LPFP on my truck makes various levels of noise depending on the day. Some mornings it is normal and some mornings it is louder. I don't know why especially when it can be the same tank of fuel.

 

Before the days of the serpentine belt, we had a cat that knocked all of the belts off the front of the engine with his tail. He was lucky he kept his tail, and we were lucky we could put all of the belts back on and have no further damage. He stopped seeking shelter under the hood after that.

 

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Did you ever find out what it was?