Date: Mon, 13 Jul 2015 13:39:08 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Fwd: Re: ECU Testing
In-Reply-To: <55A2BF6A.6040102@ucsb.edu>
Content-Type: text/plain; charset="iso-8859-1"; format=flowed
This is just Darrel Boehler's Digitool (second
version, with the voltmeter) with minor
variations in a prettier box. As Darrel said, it
doesn't do anything you can't do with a voltmeter
and a couple of needles to pierce insulation.
It gives LED indicators for things like fuel pump
power, Throttle switch, and so forth, and a
voltmeter that can be switched to look at Temp-I,
Temp-II, AFM output, O2 sensor output and so
forth. The ideal way to attach it would be with
a pass-through connector, but to do that you'll
need a sacrificial ECU and harness to get the
male-female pair of connectors from. Given that
much you could also arrange to have two DB-25
connectors mounted so you could plug it in
configured for either 1.9l or 2.1l ECUs.
The LEDs give instant confirmation about what the
ECU thinks is happening, for example that the RUN
signal for the fuel pump is being asserted or
that Hall pulses are being received. Likewise
the voltmeter lets you see what the ECU is basing
decisions on, which is the voltage at the various
sensor inputs. These inputs are supplied with
+5V through resistors, and those resistors
together with the varying resistances of the
senders form voltage dividers where the voltage
the ECU sees is 5V X (Rsender circuit/Rtotal).
Take Temp-II for example. The sender has a
resistance of about 6500 ohms at 0C, around 2500
ohms at 20C and around 200 ohms at 100C. I just
measured 8220 ohms across what I think is the
right resistor on a bum 1.9l ECU board. That
would give a reading of about 3.9V at 0C, 1.2V at
20C, and .12V at 100C -- but if the reading is 5V
then there's an open circuit, probably bad
contact between sender and its connector.
The AFM is itself a potentiometer, that is a
voltage divider where a variable wiper moves
along a fixed resistance, dividing it into two
resistances with the voltage at each point
following the same proportions as above, Vwiper =
Vinput X Rwiper-to-ground /Rtotal. The ECU
supplies the 5V on another lead, but reads the wiper voltage.
The oxygen sensor is a special case -- it's
really a battery that operates when it's very
hot, and suppplies roughly .1-.9V depending on
whether there's more oxygen inside it or outside
where the exhaust is passing by it. It's a weak
(high-impedance) signal but the ECU supplies an
even weaker one just below half a volt so that it
can tell when the sensor comes on line and starts to generate its own signal.
Yours,
David
At 03:26 PM 7/12/2015, John Goubeaux wrote:
>This is all good info to know, Thanks.
>
>I did quickly read through all the documentation on the ECU monitor I
>got, ( an 8691V ) and saw that it WOULD entail opening and soldering
>onto the contacts on the board, but once that's done and the ribbon
>cable is routed out of the ecu it's not something that has to be messed
>with again, and as you say one can route the cable either fwd or aft to
>monitor the engine performance while working or driving.
>
>I DO need to get a cable or section to solder on to the ecu as this was
>not included, ( presumably it was soldered onto another ecu ) but as
>mentioned it appears that there might be an improved method to connect
>into the ecu ? I see that VC sells a cable kit as well, not sure if
>this has what I need or?
>http://www.van-cafe.com/home/van/page_1027_126/diagnostic-tool-ribbon.html
>
>I like that it has helped you work through and solve running issues AND
>I'm, as a tinkerer and someone who is also keeping an old Vanagon on the
>road, interested in learning more about how all the Digifant ignition
>components work together.
>
>-john
>
>
>On 7/12/2015 11:31 AM, John Rodgers wrote:
>>I have the Shoebox ECU monitor. I got it without the ECU and did my own
>>soldering and wiring. Unless you are good with fine work and soldering,
>>don't.
>>
>>To get best use of the thing, knowing how to interpret the thing is half
>>the battle. Big advantage is you can have it back by the engine while you
>>work and also up front while you test drive.
>>
>>The first time it helped me isolate a bad coil. Had no coil signal.
>>Replaced coil and it fired right up. DSecond time it was a bad ECU. I don't
>>remember exactly the interpretation. But once I decided that was the
>>problem and swapped out, all was well. I just finished reworking the
>>throttle switch. It was so easy to adjust with the ECU monitor. One time
>>the hall sender didn.t light up. Replaced it and all was well.
>>
>>The system works pretty good. Saved me a lot of time and headache..
>>
>>It's a worthwhile gadget in my opinion.
>>
>>John
>>---------- Forwarded message ----------
>>From: "Neil N" <musomuso@gmail.com>
>>Date: Jul 12, 2015 12:57 PM
>>Subject: Re: ECU Testing
>>To: <vanagon@gerry.vanagon.com>
>>Cc:
>>
>>I had a quick look at the Shoe Box website and the PDF for this unit.
>>I didn't see installation instructions but looking at van-cafe and Shoe Box,
>>it appears that a known good ECU is supplied with the 'ready to go'
>>monitor.
>>
>>I swear I recall that some folks might've soldered the Shoe Box
>>connector wires to
>>existing wires at ECU connector. But looking at this Digijet ECU image:
>>http://images.thesamba.com/vw/gallery/pix/1190386.jpg
>>I can see how those pins would be more forgiving in terms of soldering
>>new wires on.
>>
>>As to my earlier speculation on what the monitor does, from the PDF:
>>
>>"Basics
>>It is important to keep in mind as you are using this System as a
>>troubleshooting tool, the monitor and ECU simply allow the user to
>>monitor input and output signals at the ECU......"
>>
>>So it measures inputs AND outputs.
>>
>>I'd suggest that for an experienced hard core enthusiast or mechanic,
>>this tool would be
>>a really useful time saver.
>>
>>Neil.
>>
>>On 7/12/15, Richard Smith <richard_smith@gnwc.ca> wrote:
>>
>>.....
>>
>>>I looked at the process of adding the shoebox thing and backed off when I
>>>saw that I had to get in there and mess with the ECU itself. It would be
>>>so nice if there were some sort of ³reader² that you could put inline
>>>(some sort of passthrough connector) without messing with the ECU itself.
>>>But that¹s probably asking way too much.
>>
>>
>>
>>--
>>Neil n
>>
>>Blog: Vanagons, Westfalia, general <http://tubaneil.blogspot.ca>
>>
>>1988 Westy Images <https://picasaweb.google.com/musomuso/New1988Westy>
>>
>>1981 Westfalia "Jaco" Images, technical <http://tubaneil.googlepages.com/>
>>
>>Vanagon-Bus VAG Gas Engine Swap Group <http://tinyurl.com/khalbay>
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