Date: Wed, 24 Jul 2013 12:37:21 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Fuel pressure regulator - acceptable pressure readings?
In-Reply-To: <45591212-F580-4710-ACF4-024A29419A75@SHAW.CA>
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At 12:03 PM 7/24/2013, Alistair Bell wrote:
>Well, it is a USG (US Gauge) pressure gauge. You can't be doubting
>those readings can you?
You'd be amazed at my ability to doubt gauges. I've got a lovely
little chromed-brass vacuum gauge made by USG for Gomco, the (at one
time anyway) pre-eminent maker of medical suction devices. It's
pretty, readable, responsive, and irritatingly far off.
>Yup, Bentley gives value in Bar and psi. 2.5 Bar = 36.25 psi.
>Leaving aside gauge error, I was just wondering if the extra 2psi
>would be enough to enrichen things beyond the O2 sensor's control ability.
Hollow laughter, since the ECU has the demonstrated ability to follow
a shorted sender down into super-rich will-barely-idle hell. But
remember that the system should operate (except for emissions)
perfectly with sensor and CAT removed. My California-spec '84 was
delivered that way in Germany and didn't get its CAT and lambda
sensor until it arrived in the US in 1991.
So lessee...stoichiometric mixture is 14.7:1. Best economy mixture
is about 16.7:1, best power mixture is about 13.3:1. If the system
is aiming for stoich at 2.5 bar, 38 psi will bring it rich by 4%, to
about 14:1. I don't think you have a worry. And of course the
feedback system will get its sticky fingers in there, mis-read the
misfiring cylinder as lean and screw your mixture up completely.
Yours,
David
>cheers
>
>ab
>
>
>On 2013-07-24, at 8:39 AM, David Beierl wrote:
>
> > At 10:47 AM 7/24/2013, Alistair Bell wrote:
> >> I got a value of (at idle, vacuum hose on/off) 32/38 psi.
> >>
> >> Bentley says it should be "approx. 29/36psi.
> >>
> >> I'm wondering if my readings are within acceptable range or are
> indeed too high?
> >
> > I wonder how accurate your pressure gauge is. The spec I believe
> is 2.5 bar, and your regulator certainly appears to be
> regulating. The only way to see how it's doing in transient
> response would be to use/make a differential gauge that uses
> manifold pressure instead of ambient as a reference. If you did
> that it should show a basically static reading of 2.5 bar under all
> engine conditions.
> >
> > It's a spring-loaded diaphragm blowoff valve that vents to the
> tank return line. I've never had one apart, but seems to me the
> spring could perhaps get weaker but not likely to get stronger, and
> I don't *think* there's a lot of opportunity for it to get
> sticky. The usual failure is a leaky diaphragm that pours gas into
> the manifold through the vacuum line.
> >
> > Yrs,
> > d
> >
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