Setting CIS Air-Fuel ratio

M

machschnell

New member
A long followup to Glenn's questions about setting up his A/F gauge.

I was curious how the CIS guys set their correct mixture. I've read the Bentley and the Bosch Fuel Injection manual and I understand how everything works, but I'm looking for how to set the ratio for a car that will spend most of its time running hard and revving high.

I've checked the voltage at the o2 sensor, and it bounces b/t .3 and .7, but stays mostly b/t .4 and .68 it seems - this is at an idle of 900-1000. To me, this seems very good. Problem is, i've messed with the mixture screw a few times, and when I rev the engine or hold it at around 4000, I get a voltage of .2 to .3. This tells me I'm running lean on the top end. I don't have the FTE switch engaged so I don't know how this would compensate yet. Since the o2 sensor voltage when connected isn't accurate b/c the ECU reads it and adjusts it, hiding an overly rich or lean condition - right?

If I disconnect the o2 sensor from the ECU and reads it voltage while the engine is running, will that tell me accurately if the engine is running rich or lean (higher voltage = rich, lower = lean)?

The Bosch FI manual says I can also check the duty cycle by tapping into the frequency valve. I tried this yesterday and didn't get any signal. There is a red wire and a brown w/ blue wire. I've got a good ground. Am I doing this correctly? There isn't detailed instructions for checking the duty cycle in the Bently or Bosch. From what I understand it should be around 45-50%.

Finally, how does the EGT play into all of this. I see about 1100F at idle and over 1200F at around 2k RPM. This sounds high to me. I've heard around 750F is good for idle. Any guidelines for this number?

Does turning the mixture screw a 1/4 or 1/2 turn at a time a good way to do it, is there a base setting I can set it at to start with?

Thanks for any help,
PJ


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83 Rabbit GTI - future ITB
 
PJ,

On my GP Scirocco (right now about 9.5:1 compression and a mild cam), the idle EGT is around 1100F. During the race, the EGT will go up to 1300-1400F.

I don't know how to help you with the CIS-E, since I use CIS. For the CIS racers, you can adjust the control pressure using various methods, including varying the voltage to the warmup regulator. I've got a system that can vary the voltage from 0.1V to 12V, which allows me to adjust the EGT on the fly (from the cockpit). It helps me compensate for different ambient temperatures, air density, humidity, etc. I'm running production now, but my system would be legal for IT as well.

Mark Coffin
#14 GP VW Scirocco
 
Originally posted by racer14itc:
PJ,

On my GP Scirocco (right now about 9.5:1 compression and a mild cam), the idle EGT is around 1100F. During the race, the EGT will go up to 1300-1400F.

I don't know how to help you with the CIS-E, since I use CIS. For the CIS racers, you can adjust the control pressure using various methods, including varying the voltage to the warmup regulator. I've got a system that can vary the voltage from 0.1V to 12V, which allows me to adjust the EGT on the fly (from the cockpit). It helps me compensate for different ambient temperatures, air density, humidity, etc. I'm running production now, but my system would be legal for IT as well.

Mark Coffin
#14 GP VW Scirocco
Click to expand...

Hey Mark,

I run a Rabbit GTI, so it's a CIS lambda system, not CIS-E.

I would like some details on your system, do you use some sort of a potentiometer to vary the voltage? Which wire do you hook into? That sounds much better than playing with the mixture screw during a race.

email me if you like: [email protected]

Thanks,
PJ



------------------
83 Rabbit GTI - future ITB
 
PJ,

Your fuel injection mixture can be set with a tach/dwell meter using the 4 cyl reading. Somewhere in your wiring bundle either near the brake vacuum booster or the pass side fire wall is a two pin connector hanging out with one brown wire and a blue white wire (this is the fuel mixture test port). Find the connector, stick two wire leads in it and and hook up the green side of the tach dwell to to blue/white and the black to the brown. Start your car and you can watch your oxy control box cycle through cold start to warm engine conditions and you can watch the various over rides function. When the engine warms up the oxy sensor will provide readings for fuel mixture control. You should see the dwell meter swinging from 43 to 53 (called windage) and that would be fine. If not use the 3mm wrench to adjust into that range - make little adjustments and let the car settle to the new level before adjusting again(also be sure to plug the adjustment hole when finished).

The most important thing you can do is get that Full Throttle switch hooked up - it is an over ride that signals for a full rich operation regardless of what the oxy sensor says because the throttle is wide open. At that point who cares about the rest as long as you are getting all the fuel you can at peak demand!? once set the systems really take care of themselves with little maintenence.

If you put in a fuel mixture gauge which reads off the oxy sensor you can watch the readings swing in a similar "windage" up and down as the oxy control system responds to exhaust conditions, you will also see it go full rich when the full throttle switch is engaged too, that is nice to see on the straights!!

good luck


[This message has been edited by Campbell (edited May 15, 2002).]

[This message has been edited by Campbell (edited May 15, 2002).]
 
I've worked pretty hard getting this system dialed in, trying different combinations of parts. It allows you to adjust the control pressure from around 25 to 50psi from the driver's seat while on the track. Would anyone be interested in paying a little bit for a parts list and installation instructions? It will work for both CIS and CIS-Lambda systems. It requires you to have an EGT gauge to dial in the fuel mixture. Optional, but not a necessity, is a fuel pressure gauge for the control pressure.

If you're interested, my e-mail is [email protected]

MC
#14 GP VW Scirocco

[This message has been edited by racer14itc (edited May 18, 2002).]
 
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