(Note: This page and the ones linked to this one are under construction. I am posting progress thus far in order to get the pressure gauge text and photos up and running.)

There are several system level tests involved with troubleshooting the Porsche 911 CIS.

These include:

• Fuel pressures
• Fuel volume
• Air/fuel ratio (mixture)
• Unmetered air

What tests do you need to run? First take a look at the symptom pages and possible causes. I hope to someday crosslink the tests required to each of the causes. In the meantime, look at the causes, select the most likely in your mind based on what you know the history of your car to be. As an example, if you are having a problem where one of the possble causes is a plugged fuel filter, and you just replaced it last week, choose another cause. This doesn't mean your fuel filter is guilt-free, you could have a lot a fuel tank contamination that has plugged it up again in a week's time. Use your judgement.

The fuel pressure and flow tests can track down several ills. Among them, fuel pump, check valve, accumlator, fuel filter, fuel distributor pressure regulator, and Warm up regulator problems. So you can eleminate a lot of potential problem causes with these tests.

There is nothing that is a direct subsitute for a good CO meter in determining fuel mixture related problems. While the O2 sensor can be used (both the Lamdba system on the '80 through the '83 cars , and an add-on sensor/voltmeter) this can only serve to get you in the ball-park, as there is so much variation in the conditions surrounding an O2 reading that the readings should be considered an estimation only. The baseline for doing a CO reading on the CIS system is at warm (hot) idle. This is the operating range where all the components should have reached thermal equilibrium. If the fuel system is maladjusted in this range, it won't be right any where else.

Un-metered air is air that enters your engine that didn't get there by the way of the airflow sensor, that flapper-like thing mechnically coupled to the fuel distributor. Air that sneaks past the airflow sensor will result in a too-lean mixture. Unmetered air is not to be confused with air that is bypassed around the throttle valve by one of the legitimate components of the system, including the Auxiliary Air Regulator, the Deceleration Valve, the Auxiliary Air Valve, or the idle speed adjustment screw.