Can a leaky vacuum hose cause a whistle when accelerating?

Question

My car recently developed a lot of issues that I've been working through. It needed a new EGR valve and fuel pump. But I held back on replacing the EGR because I hear a vacuum leak and I guessed there wasn't a strong enough vacuum for the EGR to work properly. Plus it recently started whistling when I accelerate!

I thought for sure the upper/lower intake must have a blown gasket (I've ham-fisted both of those b4). So I take apart, clean (didn't work), replace gaskets (didn't work), and then today a super miticulous job putting them on very carefully and according to torque specs (I listed torque specs in this post). I also held a straight edge up to the mating surfaces and they were all perfect except one of the heads (actually I didn't measure the other one) dipped down by like ...1/10mm in the center but I would think the gasket would make up for that.

Now I'm wrong a lot but I think I did the job right and I think the parts should be good. Yet I still hear the damn whistle!

I notice there is a line that connects the bottom of the upper intake to the some part by the brake booster (PA66-GF33 ). It's totally collapsed and I believe I can hear it suck air when I rev the throttle body. I just can't put enough load on the engine to tell if that's where the whistle is coming from because it only whistles while driving (cant reach it to spray carb cleaner in there).

I was imagining one of the gaskets flapping by the way it whistles but now I think it's the vacuum line.

You think that line might be it? Thanks for the help!!

Answer 1

From your previous questions, I am presuming that this engine is a petrol/gas engine.

You say that the engine only makes the leaking noise when the engine is under load. This would suggest to me that the leak is on the exhaust side of the engine, because vacuum on the intake manifold decreases with load rather than increasing with load.

At idle, your butterfly valve on your throttle is closed, so the engine is creating a large vacuum, since air can’t get in. The pipes that run to items like the brake servo/booster come off the intake manifold where the vacuum is greatest. If you open the throttle, more air can get in, therefore the vacuum drops.

On the other hand, the exhaust pressure increases with load, especially so, at the exhaust manifold.

I would check the exhaust manifold gasket for leaks. I have fixed leaking exhaust manifolds where under load the exhaust manifold gasket has acted like a reed in a wind instrument and has whistled quite loud, but again this only happened when driving hard. A small warp in the exhaust manifold can initiate a leak.

You could try bunging your exhaust tail pipe and then rev the engine, this will increase back pressure and may cause the whistle with the car stationary, helping you to locate the issue.