CISe system q's [Answers - long]

[juliemac57 at hotmail.com (Julie Macfarlane)]

My god man, that was an encyclopedia of fuel injection!

THAT must be saved as a tool for others to under stand the systems!
It will take a while, but I think I can get it from all that   :)

Much thanks.

P.S. All you guys are wonderful!



Julie Macfarlane
Menlo Park Research & Development
Internet Application Developer
www.menloparkrandd.com
www.montgomeryweb.org
Amsterdam NY





>From: Jason <jason@scirocco.org>
>To: Ryan H <rhock99@epix.net>,"Julie Macfarlane" <juliemac57@hotmail.com>
>CC: scirocco-l@scirocco.org
>Subject: Re: CISe system q's  [Answers - long]
>Date: Thu, 24 Jul 2003 18:24:40 -0400
>
>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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