Date: Sat, 11 Oct 2008 08:08:00 -0700
Reply-To: mdrillock <mdrillock@COX.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: mdrillock <mdrillock@COX.NET>
Subject: Re: Technical question re: Injector firing signal
In-Reply-To: <96c89c360810110521o4924e4b2y6dac9b476d243ad6@mail.gmail.com>
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There was no particular procedure. I had noticed some voltage reading
variations with my newer "Digitool" from VanCafe that I wanted to reconcile.
http://www.van-cafe.com/home/van/page_820_567/8691v_electrical_diagnosis_tool.html
I also have an original homemade Digitool made by an old list member and
I noticed variations in readings when switching back and forth from old
to new test devices. I wanted to see if I could get to the bottom of
those variations, as well as improve a voltage drop the Digitool showed
at the power pin of the ECU on my 87 driver. I asked my brother to stop
by and give me a hand determining what was going on. He insisted on
using my scope rather than relying just on my multimeter. We looked
first at the supply voltage at it's source, the alternator. A nice 13.99
volts with the meter but the scope showed more noise there than
expected. Next was the power junction stud in the engine compartment
wiring box where the power wire from the alternator connects to the fuel
injection harness. There we could see some of the noise was actually the
voltage spiking down close to zero in a regular pattern, also causing
the multimeter to display a lower voltage since it averages the voltage.
I reach over and unplugged the idle valve connector and the spikes on
the scope stopped and the voltage reading on the meter and Digitool
increased. I plugged in a spare idle valve and the spikes returned. I
swapped the idle control 'relay' behind the passenger tail light and the
spikes were gone. I opened up the suspect 'relay' and the power
transistor was visibly smoked. I fixed a couple of these many years ago
by replacing that transistor and will likely do so again if I can find
the generic replacement number again. Anyone have that?
Mark
Larry Alofs wrote:
> So, describe your procedure yesterday, what you looked for, what you
> saw, etc.
> I most often use mine on O2 sensors too. High impedance and
> responds quickly; hard to get both features in a meter.
>
> Larry A.
>
>
> On Sat, Oct 11, 2008 at 6:49 AM, mdrillock <mdrillock@cox.net
> <mailto:mdrillock@cox.net>> wrote:
>
> Here you go Scott. Plenty for simple automotive use.
>
> http://sfbay.craigslist.org/sby/sys/873977808.html
>
> I mostly use mine for oxygen sensor testing but it sometimes helps me
> with other problems. Yesterday I found a bad idle control unit
> with it.
>
> Mark
>
>
>
> Scott Daniel - Turbovans wrote:
>
> hey there.
> I've not heard of an electronic flea market, tho there may be
> ones in
> Portland once in a while.
> all right .......
> well, if you see a good one, I'd go $ 200 on one, for sure,
> and pay
> shipping
> too.
> If you make a couple bucks on it, that's fine.
> I've used one before on a jet interceptor in the air force.
> would be fun to start scoping oxygen sensor output, injector
> pulse, etc.
>
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