Date: Sat, 9 Mar 2013 21:10:47 -0800
Reply-To: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Subject: Re: 84 Vanagon--Won't start at 40 degrees
In-Reply-To: <vanagon%2013030923102531@GERRY.VANAGON.COM>
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thanks for the through rundown.
I'll try the voltage method sometime.
Havn't seen an ecu do anything like this ..
other than one that held the injectors open full time continuously.
that's the only 1.9 ecu I have ever seen fail.
and I got the van that way ..
so it's even possible technician error was involved, aka boneheadedness.
I tend not to read voltages on electronic stuff unless a book says to or
I really know what I am doing.
thnx
sdf
On 3/9/2013 8:10 PM, David Beierl wrote:
> At 10:10 PM 3/9/2013, Scott Daniel - Turbovans wrote:
>> fwiw,
>> if I suspect Temsor II ..
>> which I sure would on an 84 waterboxer vanagon
>> ( or conenctions to it ! )
>> I would pull out my ohm meter and measure the reistance and compare that
>> to the chart in Bentley.
>>
>> that is there standard test there too I believe..
>> measure resistance of Temp Sensor II ..right there onthe thermostat
>> housing , or near it ..
>> two wire connector there.
>> Be *real sure* it's getting a good connections. That connector gets old
>> and can be dodgy.
>
> Hi Scott,
> In general I completely agree, and you know I've told people to do
> both those things about a thousand times or so. But there's at least
> some method in my madness.
>
> If Temp-II is causing a no-start, it has to be either
> I) not enough enrichment, because:
> a) Temp II line shorted to ground (voltage approaching zero)
> b) ECU providing insufficient drive on the line (internal pull-up
> resistor or its connections)
> c) Sender drastically low value (not very likely)
> d) ECU enrichment logic not working right
>
> OR
>
> II) too much enrichment causing flooding, because:
> a) Bad sender connection (if open circuit, voltage will be
> approaching five volts)
> b) Sender much too high value (not very likely unless moisture
> has gotten inside)
> c) ECU providing too much drive (internal pull-up resistor
> partially shorted, very unlikely)
> d) ECU enrichment logic not working right
>
> Checking the Temp-II working voltage by back-probing the connector
> will instantly show whether a problem is case I, voltage too low; or
> case II , voltage too high; and Temp I is a handy reference point
> because at equal temperatures the voltages should be very nearly
> equal. If they are, then you have largely eliminated Temp-II as the
> problem source. Bad ECU internal logic won't be detected, but
> everything else will.
>
> If they're not about equal, then it's time to start distinguishing
> farther with resistance tests. But the voltage test is very quick,
> and will detect an ECU drive problem the the resistance tests won't,
> because what the ECU is actually measuring is voltage; and there are
> things inside the ECU that can affect that voltage. Electrically,
> the ECU internally supplies +5V to one end of a resistor. The other
> end is connected to the sender which is further connected to
> ground. The pair of resistances form a voltage divider, and the
> voltage measured at the junction between the two is proportional to
> the ratio of Rsender (including connections outside the ECU and the
> ground path back to the ECU; and inside the ECU as far as the
> measurement point) : Rtotal (including all connections and ground path).
>
> There are lots of ways to get there....
>
> Yours,
> David
>
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