[T3] On my 73 square

Keith Park topnotch at nycap.rr.com
Sun Sep 15 18:45:45 PDT 2019

you really need to have a wideband on there to know what the AFR is in order
to adjust the MPS anyway, otherwise you really are shooting in the dark.


-----Original Message-----
From: type3-vwtype3.org [mailto:type3-vwtype3.org-bounces at lists.vwtype3.org]
On Behalf Of Jim Adney
Sent: Sunday, September 15, 2019 5:07 PM
To: type3 at vwtype3.org
Subject: Re: [T3] On my 73 square


Clearly I'm aware of the long history of this. The problem, as I see it, is
it's pretty clear that this is NOT a pressure sensor problem. That's because
happened suddely, and it happens with different pressure sensors. I'm here 
in the midwest with the very same car, '73 AT/FI, running the same FI system

without his symptoms.

To me, it makes no sense to mess with the pressure sensor unless we're 
pretty sure it's a pressure sensor problem.

Or, as Gene Berg would put it, "Don't put a Band-Aid on your elbow for a 
scrape on your knee."

I understand that there are people out there who jump at the chance to 
"adjust" the pressure sensor. Those same people would probably suggest 
adjusting the brain, too, if it also had a simple, one-knob, adjustment 

People tend to look at problems like this as one dimensional problems: You 
either need more or less of something. Unfortunately, even carbs are not 
one dimensional, with their interplay of main jets, idle jets, emulsion
and throttle pumps. FI is even more complicated.

I have a friend who refers to things like this as, "wandering around in a 
multi-dimensional parameter space." That may seem complicated, but it 
really puts it in a nutshell. Which are you going to adjust, U, V, W, X, Y,
Z? Any one of them can make things richer, but each has different effects, 
under different loads, and at different speeds, and their effects all

It's possible that he needs another brain to swap in, as it's always
that something really has gone wrong in there. That's just about the only 
thing he hasn't tried. That's an unlikely failure, but anything's possible.

I thought we had it fixed when he found the bad relay, but that didn't help.
possible, however, that the fix on the relay didn't last for long. There's
the fuel pump relay, and he hasn't monitored the fuel pressure while

Then there are the trigger point contacts, although those should make for 
poor operation at speed as well as at idle, which he doesn't see. Still, I'd
to see those get adjusted, because it's a common problem and is something 
simple I can do here, but it's not a DIY project.

There are so many trivial mistakes that can happen that will make things 
bad. Daniel mixed up #21 with #12 in the trigger point connector, which 
made some brains work and others not (how could that be?) That wasn't 
found until we put the Bosch tester on it. Someone else found 2 wires 
swapped on their pressure sensor connector. That kept the engine from 
running at all, but I'm amazed that he was able to find this at all. I've
the head sensor wire connected to the ground lug on the pressure sensor, 
and that car still ran, but poorly.

So, my recommendations: try a different 048 brain, monitor the fuel pressure

and the voltage to the fuel pump while driving, monitor the output voltage 
from the power relay while driving. Also see if the problem goes away if the

TPS is disconnected. Then get this car to a Bosch tester and someone who 
knows how to use it. A second set of eyes is often able to pick up a


On 15 Sep 2019 at 19:30, bobsnotch at aol.com wrote:

> That's the thing Jim, that "miss at idle" started him down this road of
going thru everything. 
> He's had a couple of threads about this on the Samba, chasing it. So far,
the big consensus 
> has been to adjust the MPS, so he can at least plug in the IAD sensor.
> The miss has been bugging him since 2016 or maybe 2017, as he can't get
rid of it. He 
> ended up unplugging the IAD TS to help a running issue back then, after he
got the correct 
> MPS on the engine (had been running a "D" unit).
> He originally blamed it on the 10% ethanol being added, but we know
better. That's not it.

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

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