Date: Mon, 12 Sep 1994 09:29:35 EDT
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: cchubb@ida.org (Chris Chubb)
Subject: Re:Computers on Board
/I wonder if there exists some sort of device that you could plug in
/between the engine (maybe the fuel injection) and the PC and then some
/software allowing you to monitor/analyze the engine. I know that --at
/least for the early fuel injected engines-- VW had a computer they used
/for diagnostics and which plugged right into some receptacle in the engine
/compartment. That might be a starting point.
I built as part of a student project oh, many moons ago, a diagnostic
program that worked on the old, OLD, Timex-Sinclair 1000's. I might even
have my write up around somewhere.
The program gave a decent approximation of RPMs, Dwell, and some
other functions I cant remember. It used a 'black box' that hooked onto
the expantion connector and the points wire of the distributor. It did
not have enough memory for me to implement the diagnostic functions
that I had envisioned, nor was the timing accurate enough. It ran off
of 12 volts, was rigged as hell and impervious to water and grime,
and used a small 12 volt TV for output.
If I were to to it again today, I would try to use a cheapo 8086
portable and implement the following functions:
Tach
Dwell
degrees between firing of successive cylinders
degrees between firing of same cylinder (timing fluctuation)
Inductive pickups on all four spark plugs. These could be cross
referenced with the points to indicate no-fires
TDC sensor with firing informaton to indicate advance. Reports
advance curve under various driving conditions.
Oxygen sensor, mabye to indicate mixture under various conditins.
If you have any suggestions, send them my way, or post them. As the list
stands right now, the black box would not be very expensive. All it would have
to do is read the various sensors, digitize the results, and serially
send them to the host PC. The host PC would be able to do all the analysis
of the data in real time, giving you information as you drive, or in the shop.
All of the sensors, (esp. the four inductive pickups) would be more expensive
than the 'black box' reading equipment. The pickups, O2 sensor, TDC sensor,
and some mounting brackets would cost about $100.00. I cant cost the rest
of the system, and the computer would be up to you. The hardest part would be
making all the logic operate reliably on 12 volts for long periods.
I have always been intrigued by the big computers at service bays, but
I realized that the snesing hardware is trivial. All of the cost of these
machines, mostly leased, is the vehicle tune-up database that they carry.
So, any ideas?
--- Chris Chubb (cchubb@ida.org)
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