Date: Fri, 22 Jul 2011 17:24:37 -0400
Reply-To: Larry Alofs <lalofs@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Larry Alofs <lalofs@GMAIL.COM>
Subject: Re: Running Rich
In-Reply-To: <1310963895.1669.6.camel@landallc>
Content-Type: text/plain; charset=ISO-8859-1
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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