Date:         Thu, 10 Apr 2003 13:09:23 -0600
Reply-To:     "Madsen, Ken" <Ken.Madsen@ATTCANADA.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Madsen, Ken" <Ken.Madsen@ATTCANADA.COM>
Subject:      Re: More rant on grounds and vanagon syndrome
Content-Type: text/plain; charset="iso-8859-1"

Could you guys point out what ground points should be checked, specifically, locations?

Ken
87GL

-----Original Message-----
From: John Rodgers [mailto:j_rodgers@CHARTER.NET]
Sent: Thursday, April 10, 2003 3:13 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: More rant on grounds and vanagon syndrome


Steve, this is a most enlightening discourse.

Do you think it possible to agressively attack the grounding issues by
installing direct ground wiring from the ECU to the engine, and from any
other questionsable locations directly back to the engine??

I remember way back in my aviation days that there were situations that
drove one crazy at times, always having to deal with what all the
aviation types referred to as "an intermitant short to ground!!"
Electrical problems both aggravating, difficult to repeat,  and
difficult to find.

John Rodgers
88 GL Driver

Steve Delanty wrote:

> Jay wrote:
>
>> Grounds and clean connections are the key. I have added extra body to
>> engine ground wires, as well as  wires from the alternator and the AFM
>> casting.  All the connections are cleaned and assembled with di-electric
>> grease.
>
>
> Grounds, grounds, grounds...
>
> I believe that part of the problem is that VW engineers violated
> one of the most important rules of good grounding tecniques
> by grounding the ECU and some of the sensors to the body of the
> vehicle and the O2 sensor (and who knows what else) at the engine.
> Good design practice would dictate grounding ALL of the EFI components
> including the ECU to the engine ONLY. (and most modern EFI systems
> go out of their way to do this)
>
> Grounding the ECU at the body and O2 at the engine means that the
> ANY resistance (and there is always some) in the ground strap from
> engine to body will cause an error voltage to be added to the output of
> the O2 sensor.
>
> Consider the following facts for your amusement...
> Under "normal" conditions the voltage output of the O2 sensor is
> approximately 0.5 volts. A voltage output of 1.0 volt would indicate an
> EXTREMELY rich condition, and a voltage of 0.25 volts would be
> extremely lean, so it's obvious that small voltage errors can make a
> pretty
> big difference between what the O2 sensor sees and what the ECU *thinks*
> the O2 sensor sees.
>
> When the alternator is producing current, the ground return path for said
> current back to the alternator travels through the ground braids.
> Since these
> braids have a finite resistance, there *will* be a voltage drop across
> them.
> How much? Well, if the alternator is producing 30 amps, and the ground
> braid resistance is 0.01 ohms, then the voltage difference between the
> body of the car (where the ECU is grounded) and the engine (where the O2
> is grounded) will be 0.3 volts, with the body voltage being positive
> relative to
> the engine. (that is the engine is 0.3 volts more negative than body)
> So... this 0.3 volts introduced by grounding errors is subtracted from
> the 0.5
> volts that the O2 sensor puts out, and suddenly the ECU only sees 0.2
> volts !!!
> Holy Cr@p!  We're way to lean says the ECU, and cranks the mixture up to
> rich as hell..
>
> The problem is worsened by the fact that the DC offset voltage caused by
> charging current is only an average, and an error of 0.3 volts will
> also have
> an AC component riding on it caused by the 3-phase alternator output,
> which
> causes the peak voltages to be much higher. Also, "Load dump" (which
> is brief
> high voltage spikes caused when electrical loads are suddenly removed)
> causes very short duration but high current spikes to pass through the
> ground braids and I saw brief voltage peaks well in excess of 1 volt
> between
> the body and engine when I was measuring. This means that the O2 sensor
> input to the ECU actually goes to a voltage BELOW ground (negative with
> respect to ground) periodically.
>
> I think the ECU just can't cope with this BS on the O2 line and
> eventually
> goes into "stupid mode" until the power is reset.
>
> Some folks have said that disconnecting the O2 sensor made their vanagon
> syndrome go away. Yep. Makes sense to me...
>
> I believe that what REALLY needs to be done, is to find ALL the wires
> that
> ground the EFI system to the body (ECU and all sensors) and remove these
> grounds from the body and ground them ALL at the engine only. Only in
> this way can all error voltages caused by charging current passing
> through
> imperfect engine to body ground straps be eliminated
>
> Since our digifants, don't do it right, the next best thing is to add
> plenty
> of extra heavy duty grounding, preferably directly from the alternator
> to some
> body point removed from the EFI ground locations. There will always be
> *some* error voltage present on the O2 line this way, but you can
> probably
> reduce it to an insignificant amount.
>
> And again, the noise suppression capacitor on the back of the alternator
> is an important item. It not only helps remove some of the 3-phase AC
> component off the charging voltage, but it helps absorb the brief voltage
> spikes caused by alternator load dump.  Get one if ya ain't got one!
>
> So there. That's what *I* thnk about digifant and it's silly ground
> system...
>
> Happy motoring!
> Steve
> '86 Westy
>