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CISe system q's [Answers - long]
- Subject: CISe system q's [Answers - long]
- From: rhock99 at epix.net (Ryan H)
- Date: Thu Jul 24 19:43:08 2003
Great explanation - the only thing I'm confused about is the mA numbers. Larger numbers are definitely leaner, while smaller numbers are richer. You can see this if you turn it clockwise as the Bentley says to richen the mixture, the numbers will lower. And you can smell the richness. Mmmm... Unburnt fuel.
>
> From: Jason <jason@scirocco.org>
> Date: 2003/07/24 Thu PM 06:24:40 EDT
> To: Ryan H <rhock99@epix.net>,
> "Julie Macfarlane" <juliemac57@hotmail.com>
> CC: scirocco-l@scirocco.org
> Subject: Re: CISe system q's [Answers - long]
>
> At 12:58 PM 7/24/2003, Ryan H wrote:
> >Well, if your car was running limp-mode, you'd really notice it, cause
> >you'd have NO power. None.
>
> She actually was -- I saw the 10mA reading.
> Whether the car will actually run like shizzynit is going to be a factor of
> where the mixture is set. I'll explain in a minute.
>
>
>
> >The connector on the back of the fuel block is what you measured (DPR)
> >that read 10mA. Not exactly sure how this unit works, though. A reading
> >that is stuck usually means a dead O2 sensor, but I was under the
> >impression by others that the reading would be 20mA in such a case, not 10.
>
> Actually, I've seen it read 0 mA with a dead O2 sensor, too. As O2 sensors
> age, they put less and less voltage out, which causes the computer to think
> the car is becoming increasingly lean. It'll compensate for it by
> richening the mixture (reducing the DPR current, eventually to 0). At some
> point, the sensor will be totally dead, and then the computer will go into
> limp-home mode. (More below).
>
>
> > And the sensor on the front really has nothing to do with the CIS-E
> > loop - it's an airflow sensor that is only used when you first start the
> > car - it supplies additional fuel when you hit the throttle for the first
> > 30 seconds or so after starting it. If you were to unplug it then blip
> > the throttle right after starting, the car would bog nicely because of
> > the missing signal. HTH.
>
> It actually works all the time -- not just the first 30 seconds. It's a
> potentiometer that measures rate of change of the airflow meter. It will
> respond by richening the mixture under any quick throttle
> transitions. Unplug it, and you'll feel no big difference under
> steady-state cruising. But any time you make a sudden downward movement of
> that pedal, the engine will bog for a second until the mixture catches
> up. There are a lot of reasons why you want a richer mixture under
> transitional throttle, but one of the big reasons this device is used is to
> compensate for the time it takes for the air flow plate to move and to
> actually supply extra fuel to the injectors when the throttle is suddenly
> opened.
>
> Julie, I recommend getting the Bosch Injection book. I'm going to look to
> see if I have it on CD-ROM (or at least parts of it) for you to
> download. It's a great resource and explains everything in great
> detail. It's very technical, but I know you'll have no problem
> understanding it.
>
> Here's the long and short of it: CIS-E meters fuel by measuring airflow
> with a plate. As the plate moves further upward in response to more air
> travelling past it, it opens 4 valves in the fuel distributor which
> increase the amount of fuel going to the injectors. It's a brilliantly
> simple system.
>
> Certain situations call for a mixture leaner or richer than the baseline
> level (somewhere around 'Stoich') [cold starting and running, overheating
> engine, throttle transitions, full throttle, fuel cutoff,
> etc]. Furthermore, using feedback from the O2 sensor, it can determine the
> *actual* mixture, and make very fast continual adjustments to even more
> precisely control mixture. The CIS-E computer sends signals to the DPR,
> which allows it to make these corrections to the mixture.
>
> There are two "halves" of the fuel distributor on CIS-E cars. The lower
> chamber is fuel pressurized by the fuel pump and sitting there waiting to
> be fed to the injectors. The upper chambers are fuel that is on its way to
> the injectors. There are two ways that fuel can pass from the lower
> chamber to the upper chambers:
> (1) Through one of the 4 valves that are opened by the airflow
> plate, and
> (2) The differential pressure regulator (DPR).
>
> If your engine is perfectly tuned, you can disconnect all of the
> electronics from a CIS-E car and it will run fine. (Mine runs
> fantastically when it's warm with no CIS-E computer hooked up to it at
> all). It will meter fuel on a purely mechanical basis (i.e. through those
> 4 valves controlled by the airflow plate), and you'll lose all the
> electronic babysitting services that the "E" added to CIS-E: It'll start
> hard, since it won't have cold-start enrichment. It'll run rough when cold
> because it won't have cold-running enrichment. It will lose some power
> under full-throttle because it can't richen the mixture. Your injectors
> won't shut off when coasting under no throttle, causing a slight backfiring
> and a reduction of fuel mileage. Your emissions will be higher because the
> computer can't adjust mixture based on O2-sensor feedback. Some CIS-E
> systems (like Mercedes CIS-E systems, for example) will richen the mixture
> at high engine temps to cool the motor down, or use an altitude-sensor to
> compensate for high altitudes...
>
> The computer does all of these neat little tricks by using the DPR. The
> DPR is a connection between the lower chamber of the fuel distributor and
> the upper chambers of the fuel distributor. It uses an electro-magnetic
> membrane that acts as a valve to allow additional fuel to 'sneak' past the
> other 4 valves and supply more fuel to the injectors.
>
> When no current is supplied to the DPR, the valve is like half closed. The
> fuel getting to the injectors is the fuel that passes by the 4 fuel
> distributor valves and through the DPR. The more current that is supplied
> to the DPR, the more fuel it allows to pass through it. (So the mixture
> will be richer for any given position of the air flow plate). Likewise,
> the less current that goes to the DPR, the less fuel that is allowed to
> pass through it, and correspondingly, less fuel is delivered to the
> injectors for any given position of the plate.
>
> If you watch what happens to the DPR after you start the car, you can see
> that it gets a high current from the computer, richening up the mixture at
> first. This value then drops to the "baseline" value, which is usually
> around 10mA. (Don't quote me on some of these numbers, every system is
> different and I never remember which is which -- Mercedes, for example,
> uses Volts instead of Amps as a measurement for the DPR). This value is
> the limp-home mode.... it's the default value that the computer picks if it
> can't figure out what else to do.
>
> If you blip the throttle, you'll see the current jump up, and then drop
> down to a negative value for a split second, and then return. What's
> happening here is that the potentiometer I mentioned earlier is seeing a
> quick change in air flow, and signaling the computer to fatten (=richen) up
> the mixture temporarily. Then, the computer sees the idle switch being
> activated, which means your foot is completely off the gas. So it turns
> the injectors off completely by closing the DPR's valve as much as it
> can. Once it returns to like 1300rpm, the fuel is switched back on, and
> the value returns to "normal".
>
> Once the O2 sensor begins to provide feedback, the DPR current will start
> to fluctuate. You'll see it rise and sink, rise and sink. This is the
> computer continually (over)compensating for the mixture. It'll go a little
> too lean, then a little too rich, then a little too lean, and so on. Any
> of the other factors we mentioned before (like fuel cutoff or cold-engine
> enrichment) will vary that current by a certain amount. So, for example,
> the DPR current (calculated based on O2-sensor feedback) will be reduced by
> a few mA to richen the mixture when the car is still a little cold.
>
> At full throttle, the computer completely ignores the O2 sensor and goes
> into a fixed enrichment mode... I can't remember what it is, but say 8mA.
>
> Remember, this current reading isn't the "mixture" reading, it's a
> *modifier.* The real mixture is determined by the air-flow plate and its
> subsequent opening of those 4 valves. The DPR current tells us how much
> the computer is MODIFYING the metering that the air-flow plate is giving us.
>
> Thus a reading of 0Ma shows is that the airflow plate is giving the engine
> too much fuel, and that the computer is telling the DPR to close its valve
> to help lean out the mixture. Likewise, a DPR current of 35mA would mean
> that the mechanical metering was giving the engine far too little fuel, and
> the computer was trying to compensate for that by letting lots of fuel flow
> through the DPR to richen the mixture.
>
> So when we look at the DPR current reading on a healthy system, we should
> see a value of something like 5mA. (Don't quote me on the numbers,
> remember). This number corresponds to the point where the
> mechanically-metered mixture is as close to "dead on" as it can get, and
> allows the DPR enough room to compensate in both directions (i.e. it can
> sufficiently LEAN or RICHEN the mixture). If you set the mixture too lean
> with the screw (mechanically), you risk having the DPR be out of range: It
> can't provide enough fuel to compensate, and even doing all it can, you'll
> still be too lean.
>
> The CIS-E box has a bunch of inputs that it relies on to determine what the
> mixture compensation (DPR current) should be. I don't remember them all
> off the top of my head, but some of them are: The idle switch, the
> full-throttle switch, the coolant temperature sensor, the thermo-time
> switch, the Oxygen sensor, the airflow plate potentiometer, and some kind
> of RPM sensor. If the computer is getting an invalid reading (or no
> reading at all) from one or more of the sensors, it will go into limp-home
> mode. Obviously, the O2 sensor is one of the most important sensors --
> without it, the mixture compensation can't happen at all -- only the
> "special" cases - like cold running, full-throttle, etc, are dealt with.
>
> If your DPR current never moves or changes, there's something causing your
> computer to just give up. You need to check that all of the input signals
> are actually getting to the computer... and that all of the things the
> computer controls (DPR, aux air bypass valve, etc) are functioning
> properly. If I remember correctly, the computer will throw in the towel if
> the aux air bypass valve is disconnected, for example. (My Mercedes CIS-E
> did...)
>
> And that's it. :)
>
> Good luck and HTH!
> Jason
>
> PS: If you know how the aux air bypass valve works, (or the Idle
> Stabilizer Valve, ISV, as it's been called), you'll recognize that the DPR
> works in a similar way. The only 2 ways for air to enter the engine
> through a closed throttle are (a) through the idle bypass, which is
> adjusted by that screw, and (b) through the ISV. If the screw is set
> properly, the ISV will be at the mid-point of its duty cycle, which means
> that it's half open. This way it has maximum flexibility to raise idle (by
> opening all the way), or reduce idle (by closing the rest of the way).
>
>
>
>
>
>
>
>
>
>
> > >
> > > From: "Julie Macfarlane" <juliemac57@hotmail.com>
> > > Date: 2003/07/24 Thu AM 07:10:59 EDT
> > > To: scirocco-l@scirocco.org
> > > Subject: CISe system q's
> > >
> > > Back at Cincy, my car was identified running on "Limp home mode". That is
> > > the current was at 10ma.
> > >
> > > Is there a "Keep your VW alive" Level description of how CISe works, what
> > > the parts do etc?
> > >
> > > I know that there are 2 electrical connectors on the fuel dist, but not
> > sure
> > > what they do or what else is used to control the system.
> > >
> > > TIA guys
> > >
> > > Julie Macfarlane
> > > Menlo Park Research & Development
> > > Internet Application Developer
> > > www.menloparkrandd.com
> > > www.montgomeryweb.org
> > > Amsterdam NY
> > >
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