Date: Sat, 23 Jul 2011 09:12:55 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Running Rich-Voltmeters
Content-Type: text/plain; charset="iso-8859-1"
For most automotive work look for a digital meter that includes a bar graph
in the display. These update faster than the number display and give a very
good indication of what is happening.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Larry Alofs
Sent: Friday, July 22, 2011 5:25 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Running Rich
The challenge here is not the low voltage, but rather the low current.
The O2 sensor is what we call a high impedance source. It can supply very
little current without its voltage dropping. If the meter used is an old
fashioned analog type VOM with a needle, it draws too much current and the
voltage you are trying to measure drops, so you don't get the proper reading
and the signal to the ECU is also disrupted.
Your old VTVM was good in this situation because it had a high impedance
(used little current) and its needle moved quickly enough to follow the
changing voltage from the O2 sensor.
Modern digital meters have a very high impedance so that is no problem.
Unfortunately most of them respond rather slowly and it would be hard to
read a changing digital display quickly anyway. The best answer is an
oscilloscope, but these cost more than most DIY mechanics want to spend for
something used infrequently.
When I don't want to drag out my scope, I generally just hook up a DVM
from Radi* Shack and stare at it for a while as the engine idles and runs at
a slightly higher speed. If the numbers change too fast for the meter to
give any steady reading, that's a good thing. If I see readings once in a
while near 0.9v and sometimes around 0.1 volts,
I figure it's probably OK. This is of course with the O2 sensor
connected so that the ECU is getting the info and operating warmed up,
presumably in closed loop mode.
have fun,
Larry A.
On Mon, Jul 18, 2011 at 12:38 AM, John Lauterbach
<jhlauterbach@bellsouth.net> wrote:
> Dennis,
>
> I remember something from a lab electronics class decades ago that the
> wrong voltmeter would give inaccurate results with low-voltage sources
> such as sensors. I didn't worry about this as long as my 1967
> Heathkit VTVM still worked. The VTVM is history. What are you using
> for a voltmeter?
>
> Thank you,
>
> John
>
> On Sun, 2011-07-17 at 23:10 -0400, Dennis Haynes wrote:
>> You can measure the voltage output of the O2 sensor to determine if it is
working and if you are actually running rich. It is unlikely that you are
running only slightly rich. The system generally works or it doesn't. When
it doesn't it can go so rich that the engine nearly dies and you will even
see black smoke. You may actually have a cylinder miss fire problem. Some
good diagnoses will help you.
>>
>> Dennis
>>
>> -----Original Message-----
>> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On
>> Behalf Of Harry Hoffman
>> Sent: Sunday, July 17, 2011 5:12 PM
>> To: vanagon@GERRY.VANAGON.COM
>> Subject: Running Rich
>>
>> Hi All,
>>
>> So the van is running rich, or at least the exhaust smell more like gas
than exhaust.
>>
>> I've got a new O2 sensor in place (it's the original 3wire one) which
I've disconnected to see if things would get better but they haven't.
>> The temp 2 sensor was recently replaced by my mechanic when he put in new
threads on cylinder 2 sparkplug.
>>
>> I've also been reading a bit online trying to troubleshoot. Here are some
things I know:
>>
>> On start the idle is just below 1k rpms and remains so while driving.
>> The throttle switch makes the "click" when moved from it's closed
position with the engine off.
>> The van is responsive in all gears and easily drives 60mph
>>
>> I don't know what else to check, so any pointers would be great. I've got
a long list of google results for "vanagon running rich" which I'm pouring
through now.
>>
>> In good news, my mechanic replaced my sender unit and fixed my odomter so
I no longer have to rely on my phone's gps to see if I'm gonna run out of
gas!!!
>>
>> Cheers,
>> Harry
>
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