Neil Scott

There is a small cylindrical device which sits in front of the top of the drivers side front strut which has two wires connected to the top (sealed in resin) and two rubber tubes leading from the bottom - one goes to a 'T' connection near the wastegate on the turbo (I think), the other goes to the plastic inlet trunking between the air filter & the turbo. Anyway when at idle it is silent but if you touch the throttle slightly it starts clicking furiously. Is this the clicking referred to on the FAQ. If not can anyone tell me what this device does and should it click?

Thanks,

Neil.

Neil Scott

Well I've managed to partially answer this question myself - Mechanic at my dealer said it was normal for it to click but when asked what it did he replied 'something to do with the wastegate'.

Neil.

Colin

This clicking is perfectly normal. The SIDC FAQ is, in my opinion, somewhat confusing in its description of the wastegate solenoid and associated components, although it is plausible that the clicking noise would be slightly louder than usual if the solenoid was close to sticking. The following text is an excerpt from a posting I recently sent to IWOC in answer to a similar question:
The device you describe is the wastegate solenoid valve: From just above idle the ECU drives it (electrically) at 14Hz with a mark/space ratio of 10 (in other words open for 63ms and closed for 7ms). This is the clicking you refer to. Now as turbo boost rises the ECU increases the mark/space ratio (in other words, the proportion of the time it is closed for gets larger) which it turn starts to open the wastegate actuator (located next to the turbo) and hence control boost pressure. Essentially it's a closed loop control system designed to regulate boost pressure to a point preset in the ECU. For a good description of this technology see www.abel-info.com/~rryder/rx7/bcontrol.html.
Out of interest, the other solenoid valve (next to the wastegate solenoid) is a changeover valve that senses boost relative to atmospheric pressure and is designed (in conjunction with the pressure sensor - which is next to it) to (a) detect overboost and (b) to check that the boost pressure sensor is working - this is extremely important - you may have heard of these horror stories of cars incorrectly applying full boost at the wrong time etc!
I'm very familiar with these bits because I'm currently developing an electronic (dashboard mounted) boost controller (and possible ignition/fuel too). I think there's plenty of scope to improve the ECU's control algorithm - which seems designed for a smooth power increase (as restricting the power slightly etc...). Note that the above information has been gathered from experimentation with my '97 model, although looking at a friend's '98 model, it appears identical.

Colin.