I have an '85 Vanagon that cannot pass california smog requirements.
Too much fuel in the exhaust. 6 to 8% rather than the required .1%.
I have replaced the following parts: Catalytic converter Air Flow Meter O2 Sensor Coolant Sensor And I did buy a replacement ECU but it would stall the engine.
Is there anywhere that I can find a description of how the fuel system operates so I can find the problem on my own. I'm good with computer systems when I know what components do, and why the do it.
Can't help with the manuals, but were you ordered to be tested at a "test only" station? If so, apply to the Cal. BAR to have them pay for the repairs, up to $500.
Not knowing anything about Vanagons, but knowing what fuel injection sytems VW was using in 85, I'll say the following:
I presume you mean 6-8% CO levels, thats pretty absurdly high. That's not a catalytic converter issue (although your catalytic converter is going to be destroyed by it pretty fast if you continue to operate the car). The computer measures the amount of air flow into the engine. It then calculates the amount of fuel to inject into the engine. The amount of fuel is roughly 1 unit of fuel per 14.7 units of air (per weight). Your car most likely has a volumetric air flow sensor so it converts (crudely) air flow in volume to weight. Correction factors are then applied:
1) If the car is cold (based on coolant temperature sensor - typically a resistor with a temperature coefficient), additional fuel is added as a percentage of the calculated fuel. The colder it is, the more fuel that is added.
2) If the car is warm the oxygen sensor input is considered. The ECU expects to see the O2 sensor alternating from "lean" (~.2V) to "rich" (~.8V). The car essentially as a slow integrator that creates a bounded output correction factor based on how long the car has been lean or rich and feeds that in. Most O2 sensors fail to "lean", which means the ECU responds by trying as hard as its allowed to make the car run richer.
3) If you come off the throttle, fuel flow is temporarily cut until you either put your foot back on the throttle or it reaches just over idle speed.
4) When you are at wide open throttle and at "high" engine speed, the ECU enriches the mixture to give you better accelleration. There will typically either be a throttle position sensor or a combination of switches that give idle or wot.
5) Sudden accelleration typically involves momentarily enriching the mixture, followed by leaning it to account for airflow dynamics in the manifold.
The fuel injectors are either going to be solenoid driven (in the case of electronic fuel injection) or fuel pressure driven (in the case of mechanical). It's possible that an injector is dirty or worn out which prevents the injector from closing and hence there is a constant leak of oil. You can test for this by removing the injecctors and sticking them in seperate containers and then operate the injectors (jumper the fuel pump relay on, and in the case of mechanical injection, raise the air flow meter, or in the case of electronic injection put 12V across the injectors). The fuel flow should be roughly equal between all of them. Otherwise the best thing to do is verify the output of the sensors and switches in accordance with your service manual.
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