Date: Sat, 19 Apr 2008 13:31:14 -0700
Reply-To: Mark Drillock <drillock@EARTHLINK.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mark Drillock <drillock@EARTHLINK.NET>
Subject: Re: Still Running Rich
In-Reply-To: <651f166d0804191233t45a496d4s92825973e7165063@mail.gmail.com>
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What you are describing is likely related to the OX sensor reading. This
area of discussion gets complex fast and I don't have time for a long
winded explanation right now. Here is a short one.
The OX sensor is ignored by the ECU until the engine warms up and again
for a short while every time the key is turned off and back on.
The OX sensor reads the exhaust fumes and signals what it sees to the
ECU. The ECU then turns down all the injectors for less fuel or turns up
all the injectors for more fuel, depending on what the OX sensor signals
is needed.
If one of the 4 cylinders has a problem that messes up the exhaust
reading, the OX sensor will tell the ECU what it sees. Unfortunately the
OX sensor only reads the total exhaust as an average of sorts of all the
cylinders. Thus the ECU will try to compensate for the wrong reading
caused by one cylinder by adjusting ALL of them. This will get the
average reading closer to correct but does so by screwing up the 3 good
cylinders. This can make the engine run poorly or nearly die. Then the
OX sensor sees the new problem and tells the ECU so the ECU adjusts the
injectors back the other way. Things run better again but only briefly
since the OX sensor again sees the original problem caused by the bad
cylinder and then the ECU again screws up the other 3 trying to
compensate for the bad average reading. This cycle can repeat endlessly.
One way of checking this is to unplug the main signal wire to the OX
sensor. This prevents the above cycle from happening and may seem to the
driver to fix things. It may make the van seem drivable again but all it
does is hide the real problem.
Mark
Aileen Boyd wrote:
> Ok. So I talked with my mechanic today and he told me he checked the
> following: Temp II sensor-Ok, ECU-Ok, put a wiring harness on-no effect. I
> drove around for a bit and the van idled so low it died once, has great
> power, then loses power without me decelerating. I can accelerate through it
> and kick it up again, but goes back down. Standing idle is fine then begins
> to run rich and putt badly. All of the negative things happen after the van
> warms up to mid-temp. If you turn it off, and then start it again 1min
> later, all is fine until it warms again. I have had suggestions to check the
> wiring from the ECU to the van, and all air hoses. Both my mechanic and I
> are a bit stumped. Costing me mucho in diagnostic hours....ew... He is going
> to try again. Any other ideas?? Thanks so much for all everyone suggested so
> far. We've gone down the list.
> Aileen
> 88' Westfalia, Automatic
>
> --
> If not Peace, then Justice.....
>
