Date: Sun, 3 Aug 2008 22:12:11 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Heh -- I'm such a ninnyhammer
In-Reply-To: <48965430.9050802@gmail.com>
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At 05:58 PM 8/3/2008 -0700, Mike Elliott wrote:
>>Unhook the sensor from the AFM and leave it hooked to your dash
>>meter. If you want to know when it's hot and working, bias it to
>>0.5 volts with about a megohm so it will read midscale while it's
>>cold, otherwise it will read lean.
>
>Can do. So what am I looking for?
Is it crappy lean, or is it crappy rich. But I have an hypothesis
that connects the dots here to some extent. Stipulate AFM circuit
(AFM itself or ECU or *possibly* wiring -- as you know I'm betting on
ECU) working poorly. You start opening the throttle -- ECU doesn't
get the word as it depends on AFM. Mixture goes way lean and engine
coughs and sputters. O2 sensor steps in, says TOO LEAN and a few ECU
cycles later (several seconds at low rpm) the mix is a lot richer and
motor runs ok.
If this were the case I'd expect that you'd notice crappy throttle
response if you have a heavy foot, but with a light foot it might
just work -- the response time gets faster proportionate to the
engine rpm. But your meter ought to show it dipping lean every time
you increase throttle, then returning -- with the sensor in circuit
doing its job. With it out of circuit, I'd expect to see it go lean
and stay there while the engine coughs its lungs out.
If this is the case, substituting the Known Good ECU should make
things run right w/o the sensor in circuit.
And if your shop is doing any kind of troubleshooting without
disconnecting the sensor first, that says they fundamentally Don't Get It.
>>Mixture is controlled by fuel pressure regulator,
Not likely to be a thermal issue.
>Not tested. I's afeared of spraying gasoline.
Run the tests in Bentley for pattern and delivery...
>>injector timing/drive from ECU,
>
>Dunno how to test. Could a moderately-skilled Vanagon shop test
>this? procedure & specs?
Probably way beyond our pay-grade...
>>AFM,
If you have access to an oscilloscope, look at the AFM signal -- it
should be clean and proportionate to flap opening, not full of crappy
transients. Ditto the injectors, should see a cleanish (some ringing
maybe from injector inductance?) square wave with duty cycle varying
in response to throttle, load, rpm. Should be the same on all
injectors, i.e. if you invert one and add it to a second one the
result should be fairly close to a straight line. If you're using a
Tektronix scope remember that signal ground in the scope is tied
directly to earth ground!
--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage," '85 GL "Poor Relation"