CISe system q's [Answers - long]

[roccit_53 at hotmail.com (C Boyko)]

Jason is my hero, but he already knows that...(along with a multitude of 
others)
But how do I fix the peeling paint on the cup holder in my car? (whoops, 
that's the Newbeetle list). This list is awesome. (BTW, I hit print REAL 
fast on that one)
Cathy


>From: "Julie Macfarlane" <juliemac57@hotmail.com>
>To: jason@scirocco.org, rhock99@epix.net
>CC: scirocco-l@scirocco.org
>Subject: Re: CISe system q's [Answers - long]
>Date: Thu, 24 Jul 2003 23:24:00 +0000
>
>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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