Technical Squealing Multijet

[Cinq999]

I picked up a 06 plate MJ a few weeks ago.

Only done 69k, and is in excellent condition.

To cut a long story short, it's developed a rather horrible sounding "squeal" sound when under boost.

The only way I can describe it, is when you let air out if a balloon, and you stretch the opening, so it makes a high pitched squeal.

Only happens when on boost driving.

I solved part of the issue by fitting a shorter aux belt, and bypassing the AC condenser, as I could hear the pulley rumbling, and the "metallic" squeak then disappeared, but still the high pitched squeal on boost.

So, I then fitted new high torque clips on all the intake pipework, thinking it may be a leak at a joint. Even took the airbox off, and made sure the lid over the filter was on properly.

Took it for a test drive.....great.....squeal had gone.

Parked up, restarted, and the engine light popped up. Long story short, I'd forgotten to plug the MAF plug back in

Plugged it in, then went for a drive. Almost immediately, the squeal was back.

Again, cut a long story short, the squeal only happens when the MAF is plugged in.

Checked boost pressures with it plugged in and unplugged, and only does it when it's plugged in, regardless of boost pressure.

So.....its obviously something that is being electrically operated when the MAF is plugged in.

Could it be the EGR valve?

Wondering if when unplugged, it leaves the valve shut by default, but when plugged in, operates the valve, and potentially a leak somewhere in the valve or pipework??

 

[bugsymike]

I picked up a 06 plate MJ a few weeks ago.

Only done 69k, and is in excellent condition.

To cut a long story short, it's developed a rather horrible sounding "squeal" sound when under boost.

The only way I can describe it, is when you let air out if a balloon, and you stretch the opening, so it makes a high pitched squeal.

Only happens when on boost driving.

I solved part of the issue by fitting a shorter aux belt, and bypassing the AC condenser, as I could hear the pulley rumbling, and the "metallic" squeak then disappeared, but still the high pitched squeal on boost.

So, I then fitted new high torque clips on all the intake pipework, thinking it may be a leak at a joint. Even took the airbox off, and made sure the lid over the filter was on properly.

Took it for a test drive.....great.....squeal had gone.

Parked up, restarted, and the engine light popped up. Long story short, I'd forgotten to plug the MAF plug back in

Plugged it in, then went for a drive. Almost immediately, the squeal was back.

Again, cut a long story short, the squeal only happens when the MAF is plugged in.

Checked boost pressures with it plugged in and unplugged, and only does it when it's plugged in, regardless of boost pressure.

So.....its obviously something that is being electrically operated when the MAF is plugged in.

Could it be the EGR valve?

Wondering if when unplugged, it leaves the valve shut by default, but when plugged in, operates the valve, and potentially a leak somewhere in the valve or pipework??

It may be worth doing a "smoke leak test". I had a 1.6 multijet that I spent ages checking various electrical sensors for persistent error codes and even pressure tested from turbo to inlet manifold, this showed a couple of dodgy clips but problem not cured.
In the end a smoke test showed a small pipe at back of inlet manifold from EGR was leaking pressure via a seal at inlet manifold.
Less likely but a cracked turbo housing can cause a whistle.

 

[DaveMcT]

A loud turbo whistle can be caused by damaged turbine vanes.

 

[Cinq999]

It was a rubber hose connected to the EGR valve.....tiny air leak seeping past a clamp when EGR opens up.