Date: Sun, 16 Sep 2007 10:22:17 -0700
Reply-To: Michael Elliott <camping.elliott@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Michael Elliott <camping.elliott@GMAIL.COM>
Subject: Re: Rich on side, lean the other?
In-Reply-To: <vanagon%2007091612300396@GERRY.VANAGON.COM>
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Hi Geza, Good questions and points.
On 9/16/2007 9:29 AM Geza Polony wrote:
> Do you KNOW the two cylinders are running lean/rich, or are you just looking
> at the plugs and surmising?
That second thing. No got a sniffer. I'm planning to check the temps of
the exhausts on Tuesday to see if one side is markedly hotter than the
other, but that's the extent of my diagnostic equipment.
> There are a ton of things besides the mixture
> that can make plugs look whiter in one or more cylinders, eg., certain oil
> additives, a water leak into the cylinder, etc.
I /hope/ I don't have a water leak. Had the heads patched and resealed a
couple years ago. No sign of coolant loss.
> NGK has a site with pictures
> that gives a good clue as to what the plug appearances actually mean. I'll
> see if I can relocate it.
I have seen that site in the past sometime, too.
> Any way you could post pics of the plugs?
Maybe Tuesday. Thanks.
> Your O2 sensor isn't the problem. There's no way it could make only two
> cylinders run leaner or richer.
I know it doesn't influence individual cylinders, it just reads the summed
output of all four cylinders. If two were running lean for some reason
(funky injectors, air leaks, perverseness) then the overall mixture would
be lean and the ECU would want to richen it and would do so by squirting
more through all the injectors -- since it assumes they all are working
fine -- which would cause the cylinders that had good injectors to be too
rich. At the moment I don't have any reason to think the O2 sensor is
faulty. On the highway the output of the sensor is skewed toward lean (see
http://camping.elliott.googlepages.com/poormileage for why I think this,
which doesn't help explain my poor mpg, but that's a different story), but
I'm gonna replace the sensor anyway because I saw quite a bit of noise on
its signal when I was monitoring its output on the scope. What the heck,
easy to do.
> I don't see how any other central fuel
> delivery component such as the FP regulator or pump could cause two
> cylinders to run lean/rich, either. These provide equal pressure and flow to
> all injectors, even when they're faulty. They don't choose.
Yes, that seems apparent.
> Have you done the Bentley "ECU pin test"? Since it's free, that would be a
> good place to start in chasing down your problem. If the resistance in two
> injectors is markedly different from that of the other two, it might
> indicate a problem along the lines of what you're talking about.
I'll be molesting the injectors on Tuesday, and hope to be able to measure
spray patterns and injector + wire DC resistances to ground.
> If you've recently run any oil additives, change your plugs and drive a
> hundred miles, then reexamine. If you're losing any coolant at all, and the
> plugs on one side are whitish, that could explain where the coolant is going.
>
Good suggestions. No indication of coolant loss, and no oil additives have
been added since I got Mellow Yellow 5,000 miles ago.
--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
KG6RCR
