[T3] 1971 fuel injected fastback

[William Jahn]

One way with a T-4 of even a T-3 engine in a type-3 is to use a battery
cable clamped the the alternator mount to the battery ground just to rule
out the tran's ground as long as the battery to frame/pan is clean. I can
get 14VDC at mid RPM yet never over this. A voltage drop is the best way to
find either a positive or negative issue. Also the reading all depend o
just how accurate the voltmeter is whether a DOM or a dash mounted
Voltmeter if you are monitoring there while driving. On a generator you
will never have  14 volts at idle an alternator you will. Even at idle with
a generator it will be far below 14 volts yet does not affect the FI or
contribute to rich running it's only when the voltage drop is below a
charged battery voltage below 12 volts it begins the rich black smoke
issue. Even on a working system run it long enough with the headlamps on
and wipers and if you don't drive far enough you will end up with a low
battery voltage requiring the battery to be placed on a charger. This is
true whether an alt or gen.

On Thu, May 28, 2020 at 8:01 AM Jim Adney <jadney at vwtype3.org> wrote:

> 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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