polo wastegate rattle noise

[bn1986]

Hey guys,

having another minor issue with the polo, sorry ive been absent from here of late but with a mortgage, the funds to mod the polo are goneskis, and lets face it you lot don't help me with wanting to mod and upgrade her.

Anyway the story is as follows, car developed a rattle coming on boost. Got worse, took it to vwvillage, who said the flex join in my downpipe was rattling.

So I took the car to hitech mufflers and had a 3" stainless downpipe with 200cel cat made up,

Car drove like a dream the boost comes on harder (19-20 psi in first, never used to do that!), no rattle on the drive home. An hour later sitting hot, and bam the wastegate started making the same noise again.

It is worse in the shorter gears, and ive noticed it seemingly comes and goes once you've been driving a while. Seems less of an issue in 5th rolling on at 80.

When I unplug the n75 the noise doesn't seem to happen, and equally the car only boosts to about 5 psi (dunno if that's limp mode or if its just the maximum the turbo can boost without the n75 routing pressurised air to the actuator.

Im guessing its either:
a) a cracked vacuum hose from the N75 to the wastegate actuator, not enough airpressure to close the wastegate, and hence the rattle

b) faulty N75 (was replaced in 2013)

c) wastegate actuator issue (could be the actuator itself, or the rod has come loose)?

d) the internal flap in the wastegate has crapped out and it is somehow flapping around?

Anyone with an profound ideas? Ive had a vagcom scan run on it, and no boost/wastegate relevant issues were detected..

was contemplating replacing the n75 again, but don't want to waste time or money if its something else or something one of you guys has any experience with.

Hope someone has some insights.

Ben

[sambb]

I don't think a hose to the actuator would do that - you'd be getting overboost if that happened anyway. Likewise I don't think the N75 could cause a mechanical rattle in any of the parts. If it is an actuator based issue it could be a loose preload nut that would probably vibrate more at a particular spot in the rev range or a loose nut that is allowing the flapper to move. You said you had 5psi with the N75 unplugged. It should be more like 7psi so this may suggest that you've lost preload on the flapper and are leaking boost thru a loose flapper.

[bn1986]

could have been 7.. Its hella boring, and having dropped $1g on a dump pipe I was rather ****ty to say the least.

are the actuators expensive/hard to fix.

When it makes the rattle, the boost doesn't come on as quick, or as hard or peak quite as high...?

[Blue9N3]

Detonation?


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[bn1986]

Nope it's a mechanical rattle


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[sambb]

reach in behind the charge pipe from the drivers side and you should be able to get your fingers onto the actuator rod. Feel if there's any free play in the rod and if any of the nuts are loose you'll be able to feel it. If you're boosting to 20psi and have 5/6/7psi with the N75 disconected then the catuator is probably ok. Just where its rod attaches to the flapper is worth checking.

[Dugle]

I have a mechanical boost gauge that rattles when coming onto boost, took me a week to figure out what it was

[seangti]

When does it make the noise, only as it's coming on boost, or when producing full boost and stretching through the rev range?

My red car makes what seems like a mechanical noise as it's boosting, but it's actually the wastegate shattering in an attempt to control the boost as it rises and the noise comes back through the pod airfilter. We (my mechanic) were able to identify it by plumbing in some piping to a boost line and was clearly the pulsing air coming back through the system. Once it's reached full boost, it's not present.

[bn1986]

https://vimeo.com/121437502

Here's a short video for u guys to hear


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[simon k]

My red car makes what seems like a mechanical noise as it's boosting, but it's actually the wastegate shattering in an attempt to control the boost as it rises and the noise comes back through the pod airfilter. We (my mechanic) were able to identify it by plumbing in some piping to a boost line and was clearly the pulsing air coming back through the system. Once it's reached full boost, it's not present.

blast from the past...

my car has been making a noise like a cicada for the last 15,000k's - I finally thought about doing something to see what's doing it and disconnected the N75 today on the way home from work, noise went away.. I assume it's doing what Sean describes here

is it just annoying or is it doing damage to something?

[sambb]

I'd seafoam/subaru top engine clean it to rule out any gas leaks at gaskets on the hot side first. When I changed over my exhaust mani on the new car I reckon 2 bolts were still tight. Hot side leaks can flutter, squeal, whine etc which could account for it. If the noise went away with the N75 disconnected then it might point to a compressor side boost leak in the IC pipework that only breaks over above 6psi too I guess?

[simon k]

I'd seafoam/subaru top engine clean it to rule out any gas leaks at gaskets on the hot side first. When I changed over my exhaust mani on the new car I reckon 2 bolts were still tight. Hot side leaks can flutter, squeal, whine etc which could account for it. If the noise went away with the N75 disconnected then it might point to a compressor side boost leak in the IC pipework that only breaks over above 6psi too I guess?

nah, I did all of that.. intake cleaner, checked the bolts, pressurised the intake tract

it only does it when it's building revs, if I put my left foot on the brake and accelerator flat on the floor it won't do it, so I don't think its a boost leak

[sambb]

whats the preload on the actuator rod like? they say 3mm (3 full turns on the end nut) is the K03 base setting. Maybe it has insufficient pre load and the flapper is rattling over the port at anything just above spring pressure?

[simon k]

I was pretty sure I'd done it properly when I had the turbo off, but I reset it anyway, no difference - what would happen if I made it 4mm preload?

[h100vw]

I'd add half a turn at a time. As you add preload the boost profile can alter drastically. Will become peaky AF and the ecu may be unable to catch over boost occurrences . So go gently