[T3] ECU question .

[Jim Adney]

On 6 Jul 2016 at 16:33, William J wrote:

> I have the one which is an E unit that came with my 73 SB . I also
> have one that came off a 72 yet it does not have the tag on it . It
> does have the ground wire tab just like the E unit . I used it once to
> see it might change what was rich running that turned out to be low
> voltage from a bad regulator. 
> 
> All is has is a white paper tag right inside just ahead to the ECU
> connector with  this number printed on it 725734. 

I don't know if that number means anything to us.

> The only difference between the 73 Calif FI SB I have and the 72 was
> the 72 did not have the EGR and no plugs in the harness for it . It
> did have the EGR relay plus an older type cold start valve and the
> three port vacuum valve to the dual port dist vacuum advance and all
> three were mounted on the MPS bracket . It had the AH dist with the
> proper vacuum  advance 73 had the AH single . 

AE: '72 MT, dual can
AF: '72 AT, dual can
AG: '73 MT, single can
AH: '73 AT, single can

The dual vac can has different mounting holes, so that you can't 
mount it on anything other than an AE or AF. You can't mount the 
single can on an AE or AF body. (Of course, you CAN modify the body 
or the can and MAKE these fit, but Bosch made this difficult on 
purpose.)

> Both had the PCV setup and the IAD's the 72 had no pipe bolted on top
> for the EGR and on extra vacuum advance port for the like AG dist. The
> MPS on the 72 looked new and is VW # 311 906 051B. I need to look for
> the Bosch # I know it's on it . It had the ground tab as did the 311
> 906 021E that screwed to gether rather than rivets. 

The B pressure sensor is for '68-9. The rivets mean it's a late 
production replacement, made that way to make it "tamper proof." 
Probably an EPA requirement after some date.

> I have no history of the PO of either car so since the MPS on  the 72
> was new perhaps the entire bracket was removed for another car and it
> them had the EGR relay and old cold start valve on it. 

Not cold start; that vacuum relay is to enable the vac adv in top 
gear only. I usually take it out of the circuit, as the vac adv does 
almost nothing until you get to cruising anyway. California '72s had 
EGR, so it's possible that the original engine was replaced, but 
given all the other things there, the swapped mounting bracket sounds 
just as likely.  

> There's my info I have . the 73 had everything on it that was stock
> that it should have. Even the ERG valve and it's rusted pipe and
> filter that never worked. With this how would I know if the ECU from
> the 72 is compatable for a 73 ? All I know is it worked the same as
> the known E unit when I tired it many years ago. Just hoping I have a
> spare. My E unit works fine. 

The '72 E brain and '73 E brain are actually different Bosch part 
numbers. I suspect VW did it this way, meaning that the later part 
was a suitable replacement for the earlier one, but not the other way 
around. The same goes for the '72 and '73 E pressure sensors; they 
have the same E suffix, but different Bosch numbers.

Yes, you can sub a lot of these parts around and not really notice 
much difference, but there can still be differences that you don't 
see, that are undesirable. It's best to seek out the correct parts, 
rather than gamble on random ones.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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