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

[William J]

I just wanted to add to what Bob brought up on different systems through the 
years.

 The early ones had a pressure switch a TPS that was on/off and a MPS that 
handled full load enrichment . Then there was the 70's with the 4 wire TPS 
and still a different MPS and I'm not clear on what type of MPS they had yet 
the TPS did take over the enrichment at least most of it. By 72 they had the 
PCV and the full load was controlled soley by the TPS and 73 they added the 
EGR .

 Based on this the IAD went through changes the MPS and the breather system 
and the ECU . It's possible an early breather would work on a 73 since all 
it does is vent the case pressure . Yet at the same time that 3 mm ID MPS 
line restriction may very well be there to compensate for the PVC influence 
of the MPS vaccum sig . If this is the case and the early IAD's don't have 
this it may need to be removed on a 72/73 and then one may create other 
issues , perhaps not if the restricion is only to balance out the PCV vaccum 
affect and the PCV is taken out of the system.

 AS I said I have no idea what the early IAD MPS port ID size is. My only 
experience is with the 72/73 system .
----- Original Message ----- 
From: "William J" <catnine09 at dslextreme.com>
To: <type3 at vwtype3.org>
Sent: Saturday, December 09, 2017 6:52 PM
Subject: Re: [T3] On a 73 T-3 SB fuel injected auto trans pinging


> 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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