Date:         Fri, 14 Apr 2000 10:49:24 -0700
Reply-To:     Dana Morphew <kdm@WHIDBEY.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dana Morphew <kdm@WHIDBEY.COM>
Organization: Dana's Mobile Carpet Steam
Subject:      Re: The Waveform is Different. Was: Extra Grounds on 1.9l
Content-Type: text/plain; charset=us-ascii

I'm eating it up.  Please keep it coming.  One of the considered
candidates to go in my '90 is the Digifant II or CIS-E...and
yes...there...just coming over the horizon...I believe it is a trailing
line of smoke, maybe from my ship, maybe about to come in at long last.

The tranny is now ready with self-rebuilt starter (it spins like
nobodies business), diesel bell-housing installed, fresh lubed & tight
release shaft with new throw-out bearing, diesel input shaft installed,
new boots (shift rod, lever and clutch slave), Redline MT-90, and all
fresh cleaned CVs with Valvoline synthetic MoS2 grease about to be
mounted.  Little by little.

-Dana-

Frank Grunthaner wrote:
>
> Interested Parties.
>
> Surprising result. While I can't directly comment on the 1.9 L Waterboxer as
> I run a 1.8L 8V GTi Digifant in line 4, I recently discovered something I had
> not anticipated. I had always assumed that the key ground issue was contact
> to met. As in not a contact through an insulating substance (oxides, crud,
> crude oil, kerrogens, plastic, the ether, etc.). Wrong. For the electronic
> fuel injection systems, the details of the resistive path are very important.
> Stereo (big thumper) system installers are well versed in a series of
> superstitious problems related to ground loops. I say superstitious because
> they are not analytically resolved but rather empirically treated with
> warnings and a recipe for the correct way. The aluminum block/head systems we
> work with have many surface elastomers (lubricants, anti-seize, etc.) and
> thin film insulators (oxides, see above) in the series path to the battery or
> computer. Also, the engine components are actually cast of mechanical grade
> alloys (not electrical grade conductors). The actual resistance across the
> block from connector to connector (or to the ground strap) can range from a
> few tenths of an ohm to 3 ohms or even more.
>
> The surprising result is the major effect on the fuel injector trigger pulse
> waveform. I haven't quantified this yet, but I have wired in taps to follow
> the trigger (on/off) pulse waveform, the ignition coil pulse waveform (think
> rpm and tach), the spark pulse and the O2 sensor response. Without a data
> logger, I can't follow all four signals simultaneously, but I can do two at a
> time. I'm setting up for real time road test the weekend after I do the taxes
> to get true load waveforms (no dyno). And I data set is modest (related to
> the fact that I can only rev the engine for extended periods if
> she-who-must-be-obeyed is away from her post. Something about neighbors who
> can't appreciate the sweet sound of a well-tuned engine).
>
> Anyway, when I did my conversion (many years ago, diesel to gas). I placed
> the ground wire from the Digifant system that is supposed to go to the head
> to the body instead. Ground is ground I said! Well, triggered by recent posts
> by Ken Lewis over my starter saga, I rigged up a switched system to go back
> and forth (ignition off!) between the body ground and the head ground. I saw
> on the oscilloscope (250 MHz bandwidth) an amazing change in the fuel
> injector waveform, and in the O2 sensor waveform. The fuel injector pulses
> were shorter and sharper (faster rise and fall times) and the same was
> observed for the O2 signal. The integrated or mean voltage of the O2 signal
> was also different by 0.072 volts indicating a leaner running condition.
>
> It appears that even though the currents are modest the issue is at least an
> RC circuit filter modifying the input to the computer. I also find that the
> computer outputs are considerably cleaner (less high frequency noise) which
> suggest a possible ground loop problem with which the Digifant computer is
> trying to cope.
>
> Summary, more ground wire is good. Heavy ground wire is better. My friendly
> local electronic goodie store (FLEGS?) sells AWG 1, 2, and 4 insulated wire
> with solderable connectors for minimal amounts of negotiable securities. I
> now have the Digifant head ground wire in the Bentley mandated location. I
> have run an AWG #2 wire (GM side terminal 42 inch ground strap from the
> accessible (not clutch slave) starter mounting bolt to the battery, an AWG #2
> wire from the AC mount (traditional I-4 ground point) to the battery, same
> wire gauge from the coil/head mount, and from the transmission to the body.
> May soon have to adjust the rear tire pressures to compensate for excess
> copper.
>
> I will try to post waveform images after I clean everything up if there is a
> image-web-site-poster-hoster available.
>
> Sorry for the length, but I think this has big MPG and Digifant/Digijet
> gremlin implications for stock systems as well as engine swaps.
>
> Hope this helps someone,
>
> Frank Grunthaner