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

William J catnine09 at dslextreme.com
Sun Dec 10 16:14:16 PST 2017

----- Original Message ----- 
From: "Jim Adney" <jadney at vwtype3.org>
To: <type3 at vwtype3.org>
Sent: Sunday, December 10, 2017 1:29 PM
Subject: Re: [T3] On a 73 T-3 SB fuel injected auto trans pinging

>I was concerned that I was mixing up different IAD front covers when I said
> there was a tiny hole at the PCV outlet. I just went down and looked at a
> '72-3 IAD and, you're right, it does not have a tiny outlet hole. The tiny 
> outlet
> hole is only on the '68-9 IAD with the optional cold start valve. As a 
> double
> check, I also blew thru the '72-3 pipe to make sure there wasn't some
> internal restriction in there and there isn't.

 Jim ; did you notice on your 73 IAD if the MPS port has a 3 mm ID 
restrictor inside it . it's right near the end and flush can't miss it . I 
thought perhaps it was placed there to maybe compensate for the size of the 
PCV port of the IAD cover.

> Nevertheless, I don't see that system causing a problem. It's possible,
> however, that the PCV valve in the breather box has dirt in it, which 
> makes it
> stick open or closed at times. That might explain your idle variation. Try
> removing and cleaning it.

 There is a bit of dirt in the breather . It's not bad and since it has a 
sort of wall betwen the two cap sides although they are open at the top the 
PCV itself does not look bad just a bit of dried oil film on the valve 
itself it wouldn't hurt to clean it.
> I understand that you've already got the valves and timing done correctly.
> Here are some other things to try/check/consider:
> '72 & '73 MAP sensors and brains have the same VW part #, but they have
> different Bosch numbers. I've always suspected this was because VW/Bosch
> felt that the later part numbers would be backwards compatable, but this
> does not insure forward compatability. You need to make sure you have the
> '73 version of each
> The '73 brain has a Bosch part # ending in 048. (The '72 brain is 024.)
> The '73 MAP sensor has a Bosch part # ending in 116. (The '72 MAP sensor
> is 106.)

 I never looked to see if the ECU has a Bosch # it has the proper VW number 
. I would need to look . The one from the 72 has no # all I see is the clean 
area wwhere the # tag was. At the time in 97 when I was trying to pas smog 
here in Calif were are now exempt up to 74 models . I didn't have internet 
and not knowing I removed the VW E  ECU and installed the one for the 72 and 
got the same reading's based on emissions Both were just a bit rich on idle 
yet the same and both just made it at the higher RPM something like 2500 if 
I recall. Both have the ground on the ECU case as well as the thermal unit 
used for the EGR . I don't know if the 72 was a sold in Calif car didn't 
have the EGR.

 The MAP has only a Bosch number which ends in 116
> I believe you're already using the correct AH distributor.
> These parts were all developed to make the vacuum advance/retard
> distributor used in '72 unnecessary. They work together, as a team.
> Regarding your ping. My first recommendation would be to take the car for 
> a
> nice long drive. If that fixes it, great, if it does not, stop halfway 
> thru your
> drive and top up your tank with the highest octane gas you can find. If 
> this
> fixes or severly reduces the ping, you know that what you have is actual
> ping, caused by compression pre-ignition.
> If high octane gas does not change the ping, this is not real ping, but
> something else.
> (If you're already using premium gas, try regular. If going to regular 
> doesn't
> make the ping get a lot worse, then this isn't ping.)

 The Ping is gone . I did add 4 gallons of 89 octane before I put the AH 
dist in . It did strike me odd that the ping was so sudden and the first 
thing I thought was fuel since we now have the winter blend and for it not 
to ping at all then all of a sudden . Normally distibutors don't suddenly 
stick or have weights hang up . Yes if a spring breaks or maybe a fiber 
washer under one  weight cracked and fell out. This didn't happen . Over all 
since I cleaned and lubed the AH and changed the shaft shims that were worn, 
it's better since now it takes a second to return to 5 BTDC rather than 2 
minutes. Also the ping the sound I heard was quite a bit louder than a 
normal ping . It sounded like a ping , I'm familar with that sound , this 
sounded like it was timed at far more advanced than 5 BTDC . At the same 
time and I only allowed it to ping for a few seconds , I didn't feel any 
power loss . It just caught me by surprise , didn't know if it was my car or 
another car near me and as son as I backed off it was gone . The very next 
stop it didn't do it and I knew it was my car . This is what made me think 
it was the Dist .
> Regarding the cyl head temp sensor, just leave it alone. There's more
> resistance in series with that sensor inside the brain. (In the one 
> schematic
> that I've been able to find on the web, there's a 300 Ohm resistor that 
> gets
> connected in series, only at idle.) It's always possible that something 
> has
> gone wrong with the circuit inside the brain, but the brains have been
> extremely reliable over the years.

 So far as the ECU has worked as far as the fuel pump relay times out and it 
starts once I prime it a bit , Starts right up once it's been started . Yet 
there are resistors and caps and transistors in them as well as solder 
joints and anything over all these years can go out of spec especially caps 
. I've built tube powered guitar amps they don't have transitors and by 
design produce far more heat from the tubes and resistors do go out of spec 
and even new ones do not all read the same yet close enough. The caps in an 
amp are electolytic , this type is used only to filter out ripple converting 
A/C to D/C  and resisters used are high temp between these caps what they do 
is drop voltage since each tube from pre amp to power requires less voltage 
. The other caps are used in tone circuits and most often they stay within 
spec and are not electrolytic . When the power section filter caps get old 
you get noise or they leak or dry out and can short and kill the power 
transformer. Now on transister guitar amps caps last a long time .

 I imagine these ECU's can have out of spec resistors and mostly the caps . 
Yet here we have low voltage 14.5 at best and the caps are more than likely 
rated @ 25 to 50 volt yet over years if the leak or dry out then you will 
have issues As you know they really only store a charge or may be used as 
filters in these ECU's . I can't imagine changing all these ECU parts . At 
least they don't use IC's
> BTW, I believe all the VW/Bosch cyl head temp senors are the same, except
> for details like the length of the wire, the insulation, and, possibly, 
> the style
> of connector.

 Yes they seemed to replace then all with one part number long ago ending in 
041A if I recall.

 The one thing I'm still trying to understand . That's how all the issues I 
have just vanish once I unplug the air temp sensor . The miss is gone , the 
idle is stable and I no longer have that 1500 RPM when engine cold with AAR 
open . I set it @ 950 hot idle in park and it stays there . Once the AAR 
closes and it does just takes longer than it should , the idle in drive is 
850 nad always drops to 850 put it in park it's 950 . Before it was all over 
the map . This tells me it's lean if the 10% across the board rule applies , 
with what I see it seems to , I don't know the precise % yet what ever it is 
it works.
> -- 
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
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