I've recently had a new exhaust on the Zx and since its been fitted the car runs lovely other than one issue I have which I think may be linked to the acav system , when pottering around the cars fine , but under fairly hard acceleration there's a sort of pulsing / woosh/woosh noise that seems to be coming from the exhaust ?!?! The rods that are connected to the diaphragms don't seem to move either ( one used to up until around 2 weeks ago ) , the problem seems worse if the car is hot and the weather is warm ? Any ideas where to start before I replace both diaphragms for £84 .

Mark

I can not imagine what you mean by a woosh woosh sound, but if your ACAV is not working you should notice weak performance between 2000~4000 rpm and a sharp increase in power above 4000rpm.

I know it sounds ridiculous but at tickover it's lovely but on the move with a bit of throttle it's almost like a pulsing type sound coming through the exhaust ? Where's the best place to start ? Replace both diaphrams and go from there .

Mark

You should not blindly replace the diaprahms.

First make sure ACAV is not working, than determine what is at fault:
-one or two broken diaphrams
-broken solenoid
-broken returnt valve, the one between the vacuumpump and brake booster

Take your multimeter and measure the resistance of the coil in the solenoid, from memory it should be 60Ohms, but if you get no reading it is broken.

Test the diaphrams
Optical:
make sure that er aren't any cracks in the vacuumlines, or plastic parts of the diaphrams.

Mechanical:
In short, let the car idle at its idle rpm(around 850)
Give it a bit of throttle, the diamphram arms should move.
Release throttle and let the engine idle, the arms should move again.
If they don't:
Disconnect the t-piece between the diaphrams and exclude one diaphram by blocking one side of the t-piece.
From an idleing engine give it some throttle and the only connecte diaphram arm should move, if it doesn't it probably broken.
Repeat test with the other diaphram.

Thanks , I'll give it a try .

Mark

I've got to the bottom of this problem , its the Brillo/wire ring in the downpipe/cat pipe which is broken and due to the engine movement under load it is opening slightly and blowing through the poor seal . I've got one on order from the dealer and it will be fitted next week .

Mark

I've got the exhaust gasket kit fitted and the car is running like a dream , next up is MoT time and then look at getting a couple of new diaphragms for the acav system .

Mark