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Engine guides and mods

450 Cycle Valve Change

Modification Details




Cycle Valve - Fault Symptoms

If your car goes into safe mode every now and then, it could well be a faulty cycle valve.
Try pulling and refitting fuse 27. If that temporarily fixes the issue, you need a new cycle valve.

The valve can also fail in such a way that the performance is restricted but no safe mode.

If you don't like being upside down with t-rex arms trying to pull a fuse in the Roadster footwell, you can
disconnect the battery instead but it resets everything and doesn't narrow the fault down to the cycle valve.

Cycle Valve - What Does It Do?

The full name is the cycle waste gate valve. It has 2 high pressure hoses and 1 neutral hose.
The cycle valve takes high pressure air from the turbo and regulates how much is passed to the wastegate actuator.

The wastegate actuator controls how much exhaust gas the turbo converts to boost.

Any excess boost is dumped out into the TIK pipe (neutral air pipe between the airbox and turbo).

If the valve fails open, the car will over boost and will go into safe mode.
If the valve fails closed, the turbo doesn't create any (or very little) boost.

Cycle Valve Changing

Some cars like to consume cycle waste valves like sweets. Initially the cycle valve is problematic to reach but when you replace it, consider putting it somewhere sensible where you can reach it easily for next time.

There are 2 ways to get to the cycle valve. You can disconnect the TIK pipe and flip it over but access isn't great.
This is the way I do it. It's a little more involved but the access is improved which make me less agitated.

Remove the rear panels and then open the boot cover to access the top of the engine.



Use a 7mm socket to loosen the pipe clip holding the upper intercooler pipe to the throttle body.



Then, at the other end of the pipe, use the same 7mm socket to loosen one of the clips. Pull the pipe out of the engine bay.



Now the same for the lower intercooler pipe.



Use the 7mm socket to loosen the hose between the turbo and lower intercooler pipe.



Then the same at the other end of the same pipe. Then remove this pipe from the engine bay.



Now you have good access to the cycle waste valve (arrowed below).



The cycle valve is bolted to a plate using 2x E8 bolts, 1 at the bottom...



...and 1 at the top.



Access isn't great so you may need an E8 spanner.



Press the metal latch in and pull the electrical connector.



Thankfully, smart gave this connection a good amount of slack in the wiring.



Now the only thing holding the cycle valve in place is the 3 hoses.



The hoses are clamped using hose clamps (imagine that!) and these are not reusable.
The hoses generally perish anyway so your best option is to just cut the old hoses and fit new ones.

As you are fitting new hoses, you may as well make them longer and put the cycle valve somewhere accessible.

Take your hose colour of choice and...



...hose up the replacement cycle valve. Now is a good time to clamp these hoses to the cycle valve.



Put the other end of the hoses into the correct places and clamp the hoses that need it.

Refit both of the intercooler hoses.



Zip tie the cycle valve somewhere sensible like the top intercooler hose.



Next time it fails, you just have to open the engine cover and swap in a new one.

What Hoses Do I Need?

Most people just go with silicone vacuum hose as it will do vacuum (as advertised) but will be fine for boost.
You can, of course, buy rubber hose if you want but you are normally limited by colour options.

1 metre of 3mm inside diameter. Cut this into 2 lengths of 50cm.
50cm of 4mm inside diameter.

What Hoses Need Clamps?

The cycle valve has 2 hoses with a red stripe, these 2 are pressure hoses and need a clamp at each end.
The other hose is plain black and doesn't require a clamp at either end.

The cycle valve below has connections labeled F, G and H.

F to T and G to E require hose clamps.
H to B doesn't require any hose clamps.

More about these connections can be found here.



What Hose Clamps Do I Need?

Unfortunately, adjustable clamps such as Jubilee Clips aren't ideal for such small hoses.
Ideally you need ones that crimp in place using crimping pliers as shown below.



You put them on the hose and then crimp the ears together to clamp the hose securely.



Where Can I Get A New Cycle Waste Valve?

Normally this is where I would call you an idiot and suggest you go to smart for smart parts.
However, you are saved this time from ridicule as smart no longer sell this part.

So you are screwed.

Well no, not really. Thankfully this unit is fitted to Mercedes, BMW, Seat, Ford, Skoda and VW models.

The exact item is a Pierberg 7.22632.01 so get searching on eBay.


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