[T3] 1971 fuel injected fastback

[Keith Park]

Its possible that its a diode in the alternator, that was a new alternator
when I built the engine because I never wanted to have to change it again,
yea, its not coming out of there any time soon, with this setup you have to
drop the heater box. its not the regulator and all the grounds are in place
and fresh, this car has a beefed up harness for the additional electronics
with a second fuse box, so grounds were beefed up too many years ago.

The mechanical regulators with the T3 engine were this way, some peaked out
low, all couldnt keep the voltage above 14 with the headlights on (Oh yea, I
rewired my headlights to keep the low beam on when the high was on)and this
never really caused a problem per say... but when I went with the electronic
regulator on the stock engine it was rock steady at 14.4, and when I went
with electronic with the T4 alternator, that did not happen.

Keith


Topnotch Restorations
topnotch at nycap.rr.com
http://www.topnotchresto.com
71 Squareback  "Hothe"
65 Notchback  "El Baja Rojo"
93 RX7  "Redstur"
13 Subaru Outback "Blendin"
 
-----Original Message-----
From: type3-vwtype3.org [mailto:type3-vwtype3.org-bounces at lists.vwtype3.org]
On Behalf Of Jim Adney
Sent: Thursday, May 28, 2020 11:02 AM
To: type3 at vwtype3.org
Subject: Re: [T3] 1971 fuel injected fastback

Keith, Keith, Keith,

Don't recalibrate your FI to try to make up for an undiagnosed problem with 
your charging system. That charging system, like any other from that era 
that's designed to work with a 6 cell lead/acid battery, was designed to 
regulate at 14-14.4 V. There were hundreds of models of cars in the late
'60s 
to early '70s that used that same Bosch voltage regulator. They all worked
at 
the same voltage. I've worked on Type 4s and 914s and replaced VRs on 
both. They all regulate above 14 V. Modern cars use a more computer 
controlled regulation system, but they all still end up above 14 V.

All this is due to the unchanged nature of the lead/acid battery chemistry.

If you're seeing less than 14 V at medium rpm, there's something wrong with 
your charging system. The fault is either in the + or - (ground) wiring or
in 
the alternator itself. You know Ohm's law like the back of your hand. I know

you understand that 0.1 Ohm anywhere in this loop is WAY too much.  

It's possible that there's poor contact between the fan housing halves and 
the engine case, or the engine case to the tranny. All of these have to be 
good in order to get good voltage to the rest of the car. It's quite
possible for 
oxides to build up on a connection that looks just fine, to the point where 
your only real ground is thru something like the clutch and accelerator 
cables.

Another possibility is inside the alternator. Alternators produce 3 phase
AC, 
which goes thru a 3 phase full wave bridge. If you've lost a diode, you've
lost 
1/3 of your output. It's also possible to have a problem with the alternator

brushes or with the rotor or stator winding itself.

I'd start by completely removing the ground strap from the nose of the 
tranny, wire brush the corrosion off, apply some grease to prevent future 
corrosion, and reinstall the strap.

Then look for a voltage drop somewhere in the + or - wiring, simply because 
that's simple and easy to spot with a voltmeter, but keep in mind that the -

(ground) side of that loop is complicated: diodes to alternator housing to 
alternator bracket to fan housing to engine case to tranny case to ground 
jumper to pan to battery ground wire to battery - post. There are so many 
links in that chain that this is where the problem is most likely to occur.

If that doesn't pick up anything, the next thing to do is to install a low
ohm 
resistor in series with the alternator output wire and look at the voltage
there 
with an oscilloscope. You can either look differentially across the
resistor, or 
you can look, AC coupled, from ground (careful with what you think is a good

ground) to the side of the resistor away from the battery. Turning on the 
headlights and wipers will amplify the signal. You should see the ripple
from 
the rectified 3 phase output. I've never done that, but I'd expect it to be 
instructive, and I know this is one way that alternators are tested.  

It's unfortunate that the Type 4 alternator is so hard to get to, but you
may 
have to bite the bullet to fix this correctly. You'll never be happy with it
until 
you do, and we both know that this isn't ever going to be right as long as 
your car sees different voltages depending on whether you have your 
headlights or wipers turned on.

Good luck, and let us know what you find,

Jim

On 27 May 2020 at 21:13, Keith Park wrote:

> This reminds me, a seldom mentioned characteristic of D jet often not
> mentioned by the experts.  One thing that has bothered me with the T4
engine
> and its alternator is that system voltage is much less than the T3.  With
> the T3 and the electronic regulator Jim mentions below it was a rock
steady
> 14V unless maybe you had ALL the lights and accessories on.  With the T4
it
> would be more like 13-13.5, so I finally went with an electronic T4
> regulator, and again, not as high.  When driving at night with the low
beams
> on im at 13.1, with highs on its 12.8 or 12.9.
> 
> now I calibrated my D jet to run where the system voltage is so its
> compensated for, but perhaps I should see if the gas mileage is less when
I
> drive at night than during the day...

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

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