Supplementary air device/choke valve gti 8v

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rutter123
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Supplementary air device/choke valve gti 8v

Post by rutter123 » Tue Mar 03, 2015 2:07 pm

The SAD on the gti is utterly shagged and finding a Good s/h working replacement is nigh on impossible unless you want to spend approx £170 for a new Bosch unit (which i dont) the principal of the SAD is to open when cold starting letting in more air tricking the ecu into adding more fuel for the faster idle when cold, in turn slowly closing over a period of a few minutes until the engine gets to N.O.T. This is operated by a 12v supply from the ecu which powers an internal bi-metal strip to close the aperture with the heat produced from inside the engine bay to hold it closed. Over time the bi- metal loses the ability to open/close the aperture leaving it stuck in the open position causing the engine to run lean moreso in the lower rpm's, for now i have bypassed the SAD to eliminate the lean running.

My question is are there any similar devices that would do the same job? I have seen a choke valve from a 16v but not sure how it operates, does it use the same principal needing a 12v supply to operate the opening/closing? Over what period of time? The pipework connections look similar size to an 8v.

Or if anyone has a 16v choke valve kicking around maybe it could be adapted.
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Tinkley
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Re: Supplementary air device/choke valve gti 8v

Post by Tinkley » Wed Mar 04, 2015 9:20 am

Have you been able to test the bimetalic strip? They usually fail completely or work, your kettle has one, and they are pretty reliable. However your kettle one is driven by steam, and your car one by an element - the element sounds more suspect.
Any other way you can get enough heat to get the bimetallic to work, and if so can you get a temp reading for its actuation. It may be possible to use a manually controlled air feed of the exhaust manifold?

rutter123
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Re: Supplementary air device/choke valve gti 8v

Post by rutter123 » Wed Mar 04, 2015 3:27 pm

Yes the bimetal is not functioning the aperture does move slightly with heat and 12v applied but not enough to fully close, I guess over 25 years it's just lost the ability to bend, a common prob esp with pug 205`s and the like. Being a sealed unit there is not a great deal you can do to repair it.
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MULLEY
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Re: Supplementary air device/choke valve gti 8v

Post by MULLEY » Wed Mar 04, 2015 8:42 pm

Is there anyway the old shagged unit could be refurbished for a lot less than a new part?
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Re: Supplementary air device/choke valve gti 8v

Post by Way2go » Wed Mar 04, 2015 10:37 pm

MULLEY wrote:Is there anyway the old shagged unit could be refurbished for a lot less than a new part?
As the motronic BX GTi doesnt use this SAD, I couldn't say but the equivalent device on a focus is the ICV (Idle control valve) and usually it is the build up of carbon deposits that cause the malfunctions.
In the case of the ICV for the focus it can be returned to normal operation by removal from the car and cleaning with carburettor cleaner.
Perhaps the SAD can be treated the same way?
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rutter123
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Re: Supplementary air device/choke valve gti 8v

Post by rutter123 » Sat Mar 07, 2015 9:39 am

I have tried the usual 3 in 1 oil and a squirt of carb cleaner but to no effect, only cleaned air passes thru this unit so there is no carbon build up inside. The small aperture inside can be manually closed with a small screwdriver thru the hole where the pipes fit so this shows its not seized, inside the unit the bimetal pushes on a cam which operates the opening/closing of the aperture, i got one from ebay a while back but this is the same only slightly closes so i broke it open tried to bend the bimetal a little to get it to function fully which it did for a dozen times then the bimetal soon returned back to its original state.
Im looking at some way of maybe converting this unit to being manually operated via a cable, something similar to the old pull out choke knob set up as another option.
Have recently found out that Alfa Romeo also use this same unit on some of their earlier models around the same era also causing problems there amongst others.
90 BX Tzd turbo 294k SORN undergoing major surgery
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rutter123
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Re: Supplementary air device/choke valve gti 8v

Post by rutter123 » Sat Mar 07, 2015 9:42 am

MULLEY wrote:Is there anyway the old shagged unit could be refurbished for a lot less than a new part?
Ita a sealed unit so i doubt it, Bosch have new in stock £159. Ouch.

Unless a new bimetal strip can be sourced. Thats the only faulty part.
90 BX Tzd turbo 294k SORN undergoing major surgery
90 BX Tzd turbo estate 46k awaiting surgery
65 Peugeot Boxer Van the new workhorse
52 Toyota Rav4 180k Bulletproof Jap reliability