WTF does the PCT Valve actaully do??

[TenaciousC]

Hi All,

<<ERATUM : TITLE SHOULD READ PTC not PCT>>

I've been making a study of the PCV system of my 850 for some months now (maybe even years) and have finally worked out where all the hoses are supposed to go.

I am curious to learn of the functional purpose of the PCT valve (that sits on the main air intake pipe near the turbo). Everyone says we must clean it.... but no one explains what it actually does.

The connections to it are as follows:

1. Connects into main air intake.
2. Large oily breather tube which goes around to the front of the block to the top of the oil catch tank
3. Vacuum tube which goes to the left hand side if the intake manifold.
4. Electrical connection

I would assume that the valve opens to allow the blow by fumes back into the intake to be recombusted. But what is the purpose of the electrical control and vacuum tube ??

Can any one explain its workings?

Thanks in advance :

C

[p fandango]

i don't think theirs a valve there its just a small heater element

[Yosser]

i don't think theirs a valve there its just a small heater element

^^ this.

Essentially it's just a T-piece that joins the crankcase ventilation system to the air intake. The other connection is to the inlet manifold, the idea being that at idle the vacuum will draw the crankcase vapour directly into the manifold.

The electrical connection is just to a heater element that stops any water vapour freezing in extreme conditions.

And it's PTC - Positive Temperature Coefficient.

[Niles]

i don't think theirs a valve there its just a small heater element

correct, its not a valve, its an air pre heater element for warming the intake air when its SUPER cold. developed for the Swedish market when the cars were designed.
Not really required for the UK market. Its much the same as the little 'snow' guard that's clipped to the front panel covering the front air intake pipe. And......the reason Volvo stopped the 'reverse' intercooler kit was that in the Nordic winters the reverse kit was chilling the air so much that the throttle bodies could freeze up. Moving the turbo pipes to the way they are on the later ('94 ish on) was to warm the air a little in the very cold weather stop stop it freezing.
The pre heater element CAN be removed from the air intake pipe BUT it must remain plugged into the loom as the ECU will notice somethings not responding & more than likely throw up a fault code.
If you want to remove it you must pull the element, leave it plugged in and wrap/cover the element so it 'works' but will not touch anything that may damage it or be damaged by it.

Make sense???

[Yosser]

The pre heater element CAN be removed from the air intake pipe BUT it must remain plugged into the loom as the ECU will notice somethings not responding & more than likely throw up a fault code.
If you want to remove it you must pull the element, leave it plugged in and wrap/cover the element so it 'works' but will not touch anything that may damage it or be damaged by it.



Not sure if that's correct.

I have mine disconnected on the S70R and there are no fault codes.

[TenaciousC]

Thank you Gentlemen for these excellent answers. It all makes sense now.

:-)

C

[p fandango]

binned mine with no ecu faults (well no faults about that anyway lol)

just a curious question here. On BT the small vac pipe from the PCT to the inlet went via a metal tube which went around the top of the head (under the sparkplug cover), again this was done to get the heat from the engine. Was this another bit just on early 94's or did they carry in on for a bit longer