how do i adjust the cis injection?

I have been told by many that the cis injection on a '91 jetta gli is adjustable ,yet nobody really knows how. can any one help?

illraceanything,
I would post this in the VW section; if it can be adjusted, someone there can tell you how to do it and what tools to use, and how much to adjust it and …… well you get the idea.
Stay safe.
Matt Bal


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Go over to www.vwvortex.com if you haven't already. Lots of forums. The signal to noise ratio is not high, but if someone knows how to do it you'll find out there.

R

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Ron
http://www.gt40s.com
Lotus Turbo Esprit
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When I owned a CIS-injected car, there was a small allen screw at the base of the fuel distributer that you used to adjust the mixture. You might look for that.

Ron's right, Vortex is THE place on the net for VW info. But, try to have a bit more info when you ask. Like, what are you trying to do w/ the adjustment? Is the car not running right, or are you trying to tweak it? There's also a couple of books on Bosch FI that are pretty good.

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MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608

I'm assuming you've got a 2L 16valve-this is a quasi Motronic/CIS-E system. Mixture is adjusted by the 3.5mm allen located in the drilling between the intake boot and the fuel distributor. If never touched, there"s still a tamper-proof aluminum plug pressed into the hole. The plug isn't all aluminum-the aluminum is surrounding a hardened steel cup so you need to drill a small hole in the center, just big enough to get a small sheet metal screw stuck in which you can pry/pull the plug out with. Now you'll need to insert a milliamp meter in series with the differential pressure regulator (the grey box-like thing on the side of the fuel distributor with a 2 wire plug on it). Probably the simplest way to do this is to open up the harness near the plug, cut one side of it, and insert the meter across the wire ends you just created. The best way is to get a male and a female connector and make a test harness that can be inserted.
When you can measure the current, you can procede with adjustment. Start the engine cold. the current should go to a high value initially, and come down as the engine warms up. CRITICAL POINT: if the current is a large negative value cold, you need to reverse the polarity of your meter leads!
with a functioning oxygen sensor, warm control current should be +1mA to +2mA.It will wander around, perhaps 0-4mA as the oxygen sensor corrects the mixture. If it is stuck at 0mA, the ECU is not seeing a signal from the sensor and you cant't make any sensible adjustment without an exhaust gas analyzer. If it is feeding back, then adjust it as necc. More current means more fuel, less (and negative) means less fuel. Just realize that in fuctional closed loop, if the current is negative it means that the oxygen sensor is commanding the computer to hold back fuel because the mixture setting is too rich-you should lean out the mixture adjustment until the current comes up to 1-2mA. "lean-out" / "rich-in": CCW=leaner; CW=richer. If you've got your polarity reversed at this point, you'll go crazy! have fun. Phil

PS: all this is useless unless the idle switch and the coolant temp sensor work.