Sucking/Blowing air sound when accelerating?

[Captain Jack]

Gearboxes are not really known to fail on the 406s...

[BruceT]

Does it depend on speed or purely on the engine rotation speed? Mine was having some weird "whooshing" noise at over 60mph, which took me absolute ages to find. Turned out to be the radio aerial on the roof being extended too much upright generating the noise in the wind

Speed is irrelevant, just as engine speed increase. Its only happens when you really put your foot down more than half way and rev past 2400-2500

[BruceT]

Okay so accelerating in 2nd/3rd gear and dipping the clutch while keeping the throttle position the same results in the noise stopping (But then the engine is not under load)

Take it out of gear has the same affect.

I dont think its Gearbox related at all

[steve_earwig]

Know anyone with a rolling road?

Btw Welly's broken bottom mount eventually broke the flexible section on his exhaust.

[DiscoPol]

Btw Welly's broken bottom mount eventually broke the flexible section on his exhaust.

Bloody hell that sounds painful

[BruceT]

There is a Dyno place about 40 miles away...

Exhaust... hmmm could well be as the bottom mount is complety shot and is not actually attached...


Ill see if I can hear anything with the windows down...

[Panda]

This all sounds very familiar! Mine makes a faint whistling noise under the same conditions. Hardly noticeable until I tow the caravan and then its quite clear. I haven't found the problem yet but I presume it will gradually get worse and then be easier to find. I was thinking that under heavy load the engine might move slightly on its mountings and stress the exhaust, possibly opening up a slightly dodgy gasket/seal somewhere. Like someone else said, without a rolling road you're probably not going to find it.

[BruceT]

Interesting...

Its only audible when your in the car, no radio on, no ventilation fan on low or high speed.

So its quiet on mine but I think the exhaust could possibly be it but weird how it appears to come through the air vents lol

[BruceT]

Ive had the windows down while going to work and when accelerating I can hear the hissing sound from the outside

[jasper5]

I've recently fitted a new cat to a Mazda MX5 with symptoms of hissing noise from outside, blowing noise from under the bonnet, and loss of power, parts of the cat had broken up and wedged in the rear silencer, the noise was the exhaust trying to blow past the broken bits, hence the loss of power, the noise from under the bonnet was the exhaust trying to blow back through the air filter.

This might not be anything to do with yours, but some of the symptoms match.

Get someone to rev the engine whilst you listen from outside the car, also put your hand behind the exhaust and feel if there is a good pressure from the exhaust when the engine is revved....I felt poor resistance from the exhaust on the Mazda.

[Welly]

I remember my 110 used to produce a *massive* blast from the eggsauce tail just by giving the throttle a sharp stab I was quite surprised at the force of it.

[BruceT]

My car feels more pokier than my misses estate but then that has a TPS Fault and general flat spots and goes into limp mode sometimes so probably not a good comparison vehicle - lol.

My MPG has dropped from 37-38 now down to 34/34.6mpg but im putting that down to colder weather and defrost and rear screen on during my commute and heavier traffic.


I was going to say ill check the old MOT for the emmision tests... but its a diesel so nothing to see apart from a smoke test!

I will check the exhaust to see how much pressure it has...

[bangernom1cs]

HI,
I have this problem on mine and have done for a while.
As the weather is awful at this time I'll investigate when I'm feeling less 'nesh'.
This hissing problem occurs under part throttle and between 2000 and 2500 rpm and under load but is less noisy under full or very light throttle. When the windows are open its especially noticeable to the point of embarrasment.
I also have the high pitched hum after switching off. This is easy as when you pump the brake pedal it goes as the vacuum disappears from the servo.

My theory (and dont take it as fact) and a few answers possibly/hopefully.
As the Hdi engine, and economy, relies on boost from the turbo at low revs the turbo itself is designed to give most of its effort at lower speeds and boost is therefore controlled by the wastegate. This wastegate itself is controlled by vacuum from one of the bulkhead electronic solenoids powered by the brake servo exhauster pump at the end of the camshaft. The solenoid being sent electronic signals from the main ECU.
I removed the vacuum pipe from one of these solenoids that supplies the wastegate and my hissing problem completely went.

Unfortunately...so did a lot of my power! From this I concluded that the little vacuum valve's diaphragm on the turbo itself 'could' be faulty perhaps(the pipe itself doesn't appear to leak). OR it could in fact be the turbo itself. I was told that pressure seals go on the turbo and when under power both let oil into the intercooler, which I have but only negligable oil consumption, and also causes the hiss as the pressure escapes with the oil possibly, which might suggest that the wastegate and its valve is working correctly but the seals aren't? I dont really want to start swapping Turbo's unless I really have to. The car itself drives ok and seems to still have a good amount of power,no flat spots or management issues and no smoking exhaust. Just this LOUD hissing...not the faint pleasant turbo whistle it should make.
This might help or hinder but if anyone knows any more I'd also appreciate it.
It might explain why my fuel MPG is much lower than I reckon it should be.
The turbo on my car was also replaced under warranty previously but some time ago.
A complete exhaust inc. cat and flexi was fitted and didnt make any difference and the emissions pass an MOT so I rule this out too.

Tony

[BruceT]

HI,
I have this problem on mine and have done for a while.
As the weather is awful at this time I'll investigate when I'm feeling less 'nesh'.
This hissing problem occurs under part throttle and between 2000 and 2500 rpm and under load but is less noisy under full or very light throttle. When the windows are open its especially noticeable to the point of embarrasment.
I also have the high pitched hum after switching off. This is easy as when you pump the brake pedal it goes as the vacuum disappears from the servo.

My theory (and dont take it as fact) and a few answers possibly/hopefully.
As the Hdi engine, and economy, relies on boost from the turbo at low revs the turbo itself is designed to give most of its effort at lower speeds and boost is therefore controlled by the wastegate. This wastegate itself is controlled by vacuum from one of the bulkhead electronic solenoids powered by the brake servo exhauster pump at the end of the camshaft. The solenoid being sent electronic signals from the main ECU.
I removed the vacuum pipe from one of these solenoids that supplies the wastegate and my hissing problem completely went.

Unfortunately...so did a lot of my power! From this I concluded that the little vacuum valve's diaphragm on the turbo itself 'could' be faulty perhaps(the pipe itself doesn't appear to leak). OR it could in fact be the turbo itself. I was told that pressure seals go on the turbo and when under power both let oil into the intercooler, which I have but only negligable oil consumption, and also causes the hiss as the pressure escapes with the oil possibly, which might suggest that the wastegate and its valve is working correctly but the seals aren't? I dont really want to start swapping Turbo's unless I really have to. The car itself drives ok and seems to still have a good amount of power,no flat spots or management issues and no smoking exhaust. Just this LOUD hissing...not the faint pleasant turbo whistle it should make.
This might help or hinder but if anyone knows any more I'd also appreciate it.
It might explain why my fuel MPG is much lower than I reckon it should be.
The turbo on my car was also replaced under warranty previously but some time ago.
A complete exhaust inc. cat and flexi was fitted and didnt make any difference and the emissions pass an MOT so I rule this out too.

Tony

Tony.

Many, MANY thanks for this. I've bolded the top part, its EXACTLY the same as mine. I get this high pitched whine, which also stops when I pump the brake pedal a few times. I cant see the picture (Work has blocked image hosting sites) i will see when im home and ill disconnect whatever you did and report!

My MPG is also 4-5mpg less than my misses car on a very similar run so maybe our MPG are down slightly because of this.

Maybe its the actual solenoid on the bulkhead?

[Panda]

There are usually two solenoids on the bulkhead : one for turbo wastegate and one for EGR valve. Some models have a third one (something to do with brakes?). The turbo and EGR solenoids are the same so you can swap them to help you diagnose a fault.

The HDi "manual" I have says something about the signal to the solenoids being "open cycle ratio". I'm not sure what this is supposed to mean - I presume it is a poor translation from French and the signal from the ECU to the solenoid is not just a varying DC voltage but perhaps a square wave with a variable duty cycle? If anyone has checked it with a 'scope I'd be very interested to know what its supposed to look like at various rpm / loads etc.