16v has more power when motor is cold?

[amalventano@sc.rr.com (Allyn)]

Toby,
    the resistor-in-line thing might backfire on you. o2 sensors make voltage,
but are incapable of producing any kind of decent current. that is why you have
to use a digital meter to measure o2 sensor current (analog meter loads the
sensor output down, and the voltage drops because of it). the cis computer has
an extremely high input impedance for its o2 sensor input, meaning that the
current going from the o2 sensor to the cis box is so small that it probably
wont even register on a digital meter (we're talking micro-amps here). with all
of this going on, trying to drop the voltage received with series resistance
would probably be more trouble than its worth.
    what would work would be a simple op-amp circuit between the o2 sensor and
the cis box. you could make the gain adjustable, letting you dial-in just how
much % boost in fuel you want. even easier would be to skip that part of the
loop and and mess with the  resistance of the coolant temp sensor. This is
already done in the way of 'power modules' and the like, and should work for
your application.

before doing any of this, i would test the coolant temp sensor, o2 sensor, coil,
and dpr, as any of those things can cause the same symptoms.

last note: you'd be surprised just how much of a power difference can come from
warmer intake air. you'd also be surprised about just how good the intake is at
dumping the cyninder head heat into the intake air stream.

HTH
Al


----- Original Message -----
From: "T. Reed" <treed2@u.washington.edu>
To: <scirocco-l@scirocco.org>
Sent: Thursday, November 21, 2002 10:25 PM
Subject: 16v has more power when motor is cold?


> Hey all,
>
> Just got back from a drive tonight and I noticed that during the first 2
> minutes or so the car had kick ass power.. I mean, I was barely laying in
> to the throttle .. probably just a touch over half way, and the tires were
> chirping in 1st and 2nd without even trying. After the car was warmed
> up I went over the same stretch of road and while it was still fast and
> there was no "huge" reduction in power, I couldn't get the tires to chirp
> again with the same amount of throttle. Both times I was just doing my
> normal smooth declutching action.
>
> I know that's not very scientific, but I'm feeling like my motor is
> running "torquier" when it hasn't warmed up yet. Ambient air temp is about
> 50 F, but I can't imagine that cold vs. warm air could make that much of a
> difference, besides.. my engine runs cold to begin with (I never get to
> the LED on the water temp gauge)
>
> I do have my mixture set to 4 mA +/- 1 mA.. Stock is 5 mA or 10 mA
> depending on who you ask. This is a 2.0 16v with 1.8 head, BTW.
>
> I've noticed that my idle bounces a bit until the car warms up. I've heard
> that this can indicate a rich mixture, but I can't rememebr why.
>
> I suspect that what might be happening is while the car is in open loop
> mode, the mixture is not influenced by the O2 sensor and is going rich
> because of my non-stock mechanical setting of the mixture screw. But
> once the car warms up, the oxygen sensor bypasses the mechanical setting,
> leaning out the mixture and causing me to loose power..
>
> I replaced the sensor about 1.5 years ago with a universal bosch sensor
> and spliced the wires in to the original harness.
>
> So I'm wondering:
>
> - what is the difference between euro mechanical CIS for 16v's and our
>   CIS-E running in open loop mode? It seems to me like there should be no
>   difference.. in steady-state conditions the mixture is based completely
>   off of the mechanical adjust screw when in open loop mode.. it should
>   be possible to force the car in to open loop (by disconnecting the o2
>   sensor) and tune the screw to keep something just a little richer than
>   stoich. This would also preserve all the warm-up and acceleration
>   enrichment features of CIS-E (assuming they normally operate when in
>   open loop)
>
> - has anyone tried placing a resistor in line with the oxygen sensor to
>   cause its output voltage to be divided between the resistor and the
>   computer, effectively making the computer "see" a lower voltage (which
>   corresponds to a leaner mixture) and thus causing it to richen the
>   mixture on its own? It seems like this would work.. if it did then you
>   could put a potentiometer in line and tune the mixture to your liking,
>   electrically.
>
> I think I might try the latter, and borrow my friend's homemade air fuel
> meter that hooks to the o2 sensor and see if putting resistance inline
> is indeed effective in changing the mixture. First, though.. I'll need to
> put an ammeter inline with the o2 sensor and see how much current is going
> through the circuit so I can determine what range of resistance is needed.
>
> Anyway, I just thought I'd share my ideas about this since I know CIS-E is
> notorious for leaning things out in the name of fuel economy.
>
> I've thought about buying one of those euro CIS setups for $300-ish but in
> my opinion there is nothing mechanically wrong with the CIS-E I already
> have.. its more than capable of delivering the amount of fuel (and the
> proper amount, at that).. so why junk it? As an electrical engineering
> student I'm inclined to find an electrical (read: cheap; components cost
> just pennies and are readily available) solution that uses the existing
> mechanical parts and sensors to accomplish the same goal.
>
> -Toby
>
>
> _______________________________________________
> Scirocco-l mailing list
> Scirocco-l@scirocco.org
> http://neubayern.net/mailman/listinfo/scirocco-l