WUR/CPR was Re: [urq] Parts recommendations

[James Howard]

Hi Ben,

On the WR at least the layout is like this:-

http://homepage.ntlworld.com/jh.666/diag.jpg

When you say 2 lines going to CPR do you mean the 2 Teed together as per 
this diagram?

The way I understand it the WR system works as below - I think the WX is 
pretty much the same at least as far as warm up goes, not so sure about WOT 
'cause of the whole frequency valve part on the WX - but I did think that 
the duty cycle was maxed out by about 4000rpm (it is on the MB).

When the engine is cold, the thermo valve is open and the mixture is varied 
as the amount of vacuum applied to the CPR varies. - The more vacuum applied 
(ie closed throttle/overrun) the higher the control pressure and the leaner 
the mixture.
The 'base' control pressure is lower anyway as the secondary function of the 
CPR is to vary pressure with temperature.

When the engine is hot, the base control pressure is higher (because the CPR 
is hot) and the thermo valve is shut. In a non-WOT condition, only vacuum is 
applied (and held) on the CPR via the one way valve and the top connection 
of the solenoid valve.
During WOT the solenoid opens and positive pressure is then applied to the 
CPR  via the bottom connection to the solenoid valve to lower the control 
pressure and provide WOT enrichment.

Basically this vacuum system provides enrichment at partial throttle on a 
cold engine, and enrichment only at WOT on a hot engine.

I have done some tests on my CPR with a MightyVac and a fuel pressure gauge. 
As vacuum is applied to the CPR, the control pressure rises. Applying 
positive pressure to the CPR does nothing - the control pressure is already 
at it's minimum at atmospheric pressure. The vacuum system on the car 
appears to apply positive pressure to the CPR only to dispell the vacuum.

This may give some clues too, although it's WR again :-
http://www.isham-research.co.uk/quattro/wr_hoses.html

Jim.
----- Original Message ----- 
From: "Ben Swann" <benswann at comcast.net>
To: <spam.me1 at ntlworld.com>
Cc: <urq at audifans.com>
Sent: Wednesday, March 30, 2005 3:27 AM
Subject: WUR/CPR was Re: [urq] Parts recommendations


> Jim,
>
> I thought the valve opened on warmup.  Anyhow- you are probably right. 
> Just
> trying to understand how this operates better.
>
> I was wondering is there a sensible way to re-plum this to provide greater
> enrichment under boost.
>
> Also - there are two lines on the CPR/WUR.  Do you know how they operate? 
> I
> was just redoing the vacuum lines on mine and was puzzled why they did it
> this way and why both ports are used for the thermo-time switch control.
>
> Ben
>
> [Date: Tue, 29 Mar 2005 19:46:19 +0100
> From: "James Howard" <spam.me1 at ntlworld.com>
> Subject: Re: [urq] Parts recommendations
> To: "Ingo Rautenberg" <i.rautenberg at waratap.com>, <urq at audifans.com>
> Message-ID: <006301c5348f$99fd9e30$657ba8c0 at jim>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
> The thermo valve closes as the engine warms up.
> When the engine is cold, the valve is open and fuel control pressure 
> varies
> with vacuum.
> When the engine is hot, the valve is closed and full vacuum is held on the
> control pressure reg (after the 1st decel) until a WOT event when the 2 
> way
> valve on the bulkhead opens and positive pressure is allowed through to
> dispell the vacuum.
>
> The control pressure reg does not enrichen further on boost, only leans on
> vac - it is at full enrichment travel at atmospheric pressure.
>
> Ergo, without the thermo valve, you have no cold running or WOT enrichment
> control, as the control pressure reg will be maxed out at part throttle 
> even
> with a hot engine.
>
> Jim.]
>