[T3] On a 73 T-3 SB fuel injected auto trans pinging

William J catnine09 at dslextreme.com
Sat Dec 9 18:52:45 PST 2017

Yes the actual tube at it's end is rather large something like 12mm OD- wall 
say 11 mm ID then drops to 10mm OD say 9 mm ID and the hole through the back 
cover 7 mm ID . It for some reason drops in ID in three places . 7 mm ID is 
about the normal vacuum line size as the MPS . I wouldn't call it small and 
it never seemed to affect anything before. It gets the clean air off the oil 
bath . I've tried to feel the vacuum at both and I really can't feel any 
suction .

 I recall Ray saying 1.5 to 2 mm fixed . Yet his main point was the distance 
the MPS port is from the PCV port affection the MPS vacuum sig . One a T-3 
it's dead center at the rear of the IAD and the MPS port is between runners 
3 & 4 at the top it has a 7 mm ID hose yet a 3 mm ID restrictor inserted for 
a reason why who knows. On early IAD's it was at the bottom . I have no idea 
what T-4 is like.  I took these measurments off a 73 IAD I have sitting 
here. The 72 I used is the same other than the EGR tube on top after the 
throttle plate and the second port for the retard line to Dist vac can which 
I have plugged. Perhaps the 3 mm ID restrictor in the MPS port was put there 
to off set the PCV vacuum. I have no idea if the early IAD MPS port has this 
restrictor or not , perhaps someone knows.
----- Original Message ----- 
From: "Jim Adney" <jadney at vwtype3.org>
To: <type3 at vwtype3.org>
Sent: Saturday, December 09, 2017 6:12 PM
Subject: Re: [T3] On a 73 T-3 SB fuel injected auto trans pinging

> On 9 Dec 2017 at 20:58, Bobsnotch at aol.com wrote:
>> This is the 1 thing that Ray really doesn't like about the 2 cap PCV
>> system VW used. It has a bad tendency to open when it wants, and
>> causes a miss. What  most of the type 4 guys do, is to strip out the
>> guts of the valve, and add a  slug with a drilled hole in it (can't
>> remember what size right off hand) in the  vac hose to the plenum. What
>> this does is allow you to tune around the "constant  vacuum leak" of
>> the small hole. I only mention this, as all of the type 4  engines
>> (bus, T-4, 914) use that same valve set up, and have issues with it. I
>> haven't really studied how the VW designed PCV system really works, but
>> then  I've only got 1 t-4 engine here, and it's on carbs. The rest of
>> the type 3  engines are all 1 cap breather models, so no real PCV set
>> up.
> All '72-3 FI Type 3s came with the 2 cap breather system. I've had several 
> of
> them and they were all fine. No problems whatsoever. There's already a 
> tiny
> little pinhole where that air enters the IAD, so there's no way for this 
> to be
> overwhelming.
> -- 
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
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