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Date:         Fri, 26 Sep 2008 13:16:43 -0700
Reply-To:     mdrillock <mdrillock@COX.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         mdrillock <mdrillock@COX.NET>
Subject:      Re: Question about testing O2 sensor with digital meter
Comments: To: Jim Felder <jim.felder@GMAIL.COM>
In-Reply-To:  <4d1b79350809261059w659fd254gd7595d6aefa6442e@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Jim, while the Digifant system can seem mystifying at times, it is ultimately a fairly simple system to troubleshoot.

Don't give up, be persistent and logical. Take notes of what is done and any effects. If you have some parts you are trying out mark them clearly so you always know which is which. It is important to follow step by step testing procedures as this is often needed to truly find and correct the problem. I realize that many don't have the full confidence to use a multimeter but that can be essential to avoid endless parts swapping. Sure, parts fail and sometimes a fix is a simple matter of replacing a bad one with a spare. Other times this method comes up short and deteriorates into chaos. You need to learn how to use the volt meter and double check your work every time.

The sensors can be working fine but if the ECU does not see them right they might as well be dead. Measurements taken at the sensors themselves may not show what the ECU sees from them. This is something to always keep in mind. Another related thing is when you test wiring while holding the connector or wires you may be flexing it such as to hide an intermittent broken connection inside. This gives a false sense that the problem is elsewhere. I have seen this so many times....

Finally, don't skip over the basics. Go back to them now if you did so, even if in your mind this is pointless. If your van was brought to me, this is what I would do. Preconceived notions of the nature of the problem are a deadly trap for problem solving. When you seem to be at a dead end it is often because you made a wrong turn somewhere. Starting over can really help sometimes.

Check the compression in all cylinders. Closely inspect the individual spark plugs when you remove them to see if a bad condition exists on one or more cylinder.

Check the actual fuel pressure, with the engine running, and doing the vacuum compensation test step for the pressure regulator. The ECU assumes the fuel pressure is correct when it varies the opening time of the injectors to adjust the mixture.

If you have one, aim an infrared thermometer at the exhaust header right near each exhaust port. Do this quickly, going to each cylinder in turn starting with a cold engine and beginning as soon as it starts running. Keep going around the circle as it warms up, seeing that they all heat up more or less at the same rate. Harbor Fright has one on sale right now for $10.

Mark

Jim Felder wrote: > I'm about to take the car out for an errand. I'll disconnect the O2 > sensor and check the Temp II when I get back and it's warmed up. I > just put a new Temp II in this morning, BTW. > > What's the procedure for testing it? > > Jim > > > On Fri, Sep 26, 2008 at 12:56 PM, David Beierl <dbeierl@attglobal.net> wrote: > >> At 01:51 PM 9/26/2008, Jim Felder wrote: >> >>> Yes, it's hooked to the ECU. >>> >> In that case it's totally screwed up. What's the TII voltage as it warms >> up? Should drop down to ? a tenth volt or so ? at running temp. If it's >> zero, bad connection from ECU or bad ECU? If it stays high, bad sensor? bad >> ground? >> >> >> -- >> David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/ >> '84 Westy "Dutiful Passage," '85 GL "Poor Relation" >> >> > > >


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