Date: Fri, 21 Dec 2001 10:23:30 -0800
Reply-To: Mark Keller <kelphoto@ISLANDNET.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mark Keller <kelphoto@ISLANDNET.COM>
Subject: Re: Boston Bobs day at the dyno
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Hi Bob,
As you may know I have the adjustable fuel pressure regulator sold by CB
Performance. Currently I run at 45 Psi or 30 psi above atomspheric and
have enjoyed the tweaking of the AFM to accompodate this pressure increase.
A couple of thoughts I had. One is that the 22d ECU does not set a full
rich mixture at WOT like the the 22 ECU, per Darrell Boehler. Second
the BoECU seems to have a rather slow cycle for high power setting, ie
the fuel mixture stays in the lean part of the specturm too long; rather
that just setting an ideal power mixture of 12:1 vs the more less cycle
14.7 of stoimetric. The result under sustained WOT was a gradual loss in
RPM as the engine would opperate on the lean side of the gate and as it
moved to richer it would hold RPM then again lose RPM as the leaning
occured-- a rachet effect of losing RPM. I believe the "chip" reverse
this as you observed. My feeling was this may have been an engniering
design to govern the engine's for durability in the light commercial
truck operational profile; better for fleet owners, but not for tweeking power.
I conducted these test on consistent grade hill climb of about two
miles. The speed and Rpm changes at the finish were compared as I made
changes in my system. My best efforst were open loop and the AFM and
fuel pressure set to deliever a .86 volt reading on the O2 at 4400 RPM
gave me 8 mph more that Closed loop with the same fuel pressue-- a gain
of 12 mph over stock fuel pressure.
I observed in open loop, without O2 sensor feedback, that the curve on
the AFM wiper signal and spring tension coupled to the ECU RPM/ fuel map
still maintained the O2 voltage within the .3 to .7 volts during
driving. The exceptions being WOT and decel which the injector are
turned off above 2200 RPM or so. I was even able to tune spring tension
and wiper position on the system so that as the vacuum approached the 5"
mark, the fuel mixture began to move above .75 volts to the a maxium
power mixture of .86 volts, and the system would run leaner at beginning
at the 12" inches, to the .3 volts and below- thrilling! My fuel economy
is better at cuise, but less at stop and go. 22 hwy, 17 city, so my
average of 20.5 is down to 19.5-- the price of power.
Unforuntaely I can't run open loop all of the time. The fine tuning is
ok, but the ECU 22d does not use the TEMP 1 senor, air temperature, to
modify the Fuel map , except at or below freezing, where it then richens
the fuel mixtue 20%. I discussed this with Darrel briefly and he said
older 022 ECU models did not ignore the Temp 1 duining normal
operations, but the 22 D does. The upshot is that seasonal changes and
even daily changes of 10 degress affected my tune at WOT only. More
temperature swings did affect the cruise mixture.
At this point to be safe, I just take the nominal gain of 4 mph with
closed loop as opposed to an additionl 12 mph open loop at the higher
than stock fuel pressure. The O2 sensor then provides temperature
compensation until temperatures drop to 40 degrees. Then I drop the fuel
pressue a touch in the winter to avoid the chugging that occure due to
the Temp 1/ ECU low tempertaure adjustment; it still happens but for
less that 15 seconds or so, compare to a minute or more if I let the
fuel pressure stay at the summer settings. The system also passed
emmisions testing with the higher fuel pressure and closed loop. For
the cost of the fuel pressure regularor, and new fuel lines, clamps and
my labor, I feel this is a good way to increase performance and as you
mentioned, fuel mixture is one that many owner's overlook.
In the future I'd like to get an older 022 ECU that goes WOT, and uses
the TEMP 1 senor during normal operation to experiment with. BTW I've
written more about these issues and timing as well, I'm at 45 BTDC at
3000 and premium gas, Chevron 91, in the archives, just search under my name.
Sincerely,
Mark Keller
91 Carat
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