[T3] ECU question .

[William J]

this other ECU does have the EGR thermo switch on it and the bracket . 
Wouldn't this make it a 73 or 72 late ECU? I don't understand why late units 
can replace early but not the other way around.

----- Original Message ----- 
From: "Jim Adney" <jadney at VWType3.org>
To: <type3 at vwtype3.org>
Sent: Friday, July 08, 2016 5:34 AM
Subject: Re: [T3] ECU question .


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