intake manifold noise

[clemenshess97]

Hello everybody,


the last couple of weeks I noticed that I have a strange whistle sound coming from my engine, my first guess was the serpentine belt, but replacing the main belt didn't help, I took off the main belt and the AC compressor belt and let the engine run for a few seconds to be sure that the noise is not coming from one of the pulleys or the AC belt...unfortunately the noise was still there.
I also just replaced my throttle body gasket because of a hissing sound I noticed some months ago, didn't help the hissing sound.
I tried to check where the sound is coming from and my guess is the intake manifold as the sound seems to come from way up top of the engine.
I uploaded a video of the sound on youtube (

)

Also: the sound is not coming from my LPG injectors (those on top of the fuel rails)

My next guess would be a vacuum leak. The truck is a 2003 model, it turned 18 y/o this January, so maybe I should just go ahead and replace the intake manifold gasket ? If so, what else should I replace while I'm at it, MAP sensor, knock sensors, any other sensors or gaskets ?

 

[Fless]

Are you revving the engine or is it surging?

 

[clemenshess97]

Are you revving the engine or is it surging?

a friend is revving it in the video

 

[clemenshess97]

could a PCV valve or the purge solenoid cause this noise ?

 

[Mudsport96]

Best bet is to get a can of carb cleaner and just spray around the intake. If it is a leak causing the noise, the engine will respond when it pulls in the cleaner.

 

[George B]

Try cleaning the throttle body. I had a whistle on an 03 Burb that was related to that.

 

[JonnyTahoe]

What made you want to convert your truck to LP ?

 

[clemenshess97]

I'll try the carb cleaner procedure today, I'll share the results of that later when I'm back home


I cleaned the throttle body about 3k miles ago, also put in a new throttle body gasket, ...I just remembered that there was some oil in the throttle body and the intake tubing.


I have the LPG system on my truck because a gallon of gas is about 7 USD where I live (in Germany), a gallon of LPG is around 2.30 USD.
The 5.3 flex fuel engines run fine on LPG, the non-flex fuel engines may need a additive or a replacement of the stock valve seats for sintered valve seats.
I have the non-flex fuel engine in my Tahoe and have no additive or sintered valve seats, but I do check the compression regularly, only when the compression starts to go bad I'll replace my valve seats.
Also: the engine burns much cleaner, LPG has almost no combustion residues, when changing the engine oil every 6-8k miles you'd be surprised how clean it still is.

I also have regular gas though, I can choose between those two basically, I have a LPG tank where the spare tire would usually sit.
The engine needs to run on gas until the water is warm, then the LPG system can be turned on.

 

[Mudsport96]

That is very interesting. Have you calculated fuel economy on the LPG? Also have you had the computer tuned for LPG?

 

[clemenshess97]

That is very interesting. Have you calculated fuel economy on the LPG? Also have you had the computer tuned for LPG?

Fuel consumption increases by about 20% when driving with LPG, that‘s because LPG has a lower energy density than gasoline.

The system is plug&play, it has it‘s own computer that reads all the engine data via OBD, the system turns itself on when the correct temperature is reached and turns itself off when the tank is empty, also shuts itself off when it detects errors. The switching between gas and LPG is smooth, you don‘t even feel it, only way to notice is when you open the hood, because the LPG injectors make a ticking sound, sounds kinda like a diesel, but only with the hood open.
Overall it‘s pretty cool to have a bivalent driven car, it also increases the range quite a bit, the LPG tank adds about 400-450Km to the range of the standard gas tank