Ineed to know where is located the oxigen sensor in a 95 chevy astro van

It is on the side of the engine block above the starter.....a little square box with wires plugged into it.........

What engine ? Does it have CPI - center port fuel injection ?

some are worn but seem to still hold a vacuum ???? could you explain
Do you have a scan tool that reads engine sensor data ? Could have mass air flow sensor ! Crankshaft position sensor . Do you know how to test obd 1 engine sensors ? Test don't guess .
Buick Electrical Part 3 Automotive Computer Operation 1990 Buick ,chevy all the same .

Donald, You did not state the model, so I posted the link for the models I found for chevy van fuse box. Check the attached links,instruction and guides, Good luck
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The Astro Van is a rear wheel drive vehicle. The Cutlass Ciera is a front wheel drive vehicle. The transmissions are entirely different and and not adaptable.

They are the sensors that are in the exhaust. I believe that there are three in this van. Depending on what engine it has. They are the only sensors in the exhaust.

there is no relay power from control panel through pressure switchs to compressor

ignition switch not lock cylinder may need to be addjusted it's on top side of steering column under dash

The control module is located just behind the ignition coil. Sorta hard to get to but we got it and the van is running great.

the problem is common for the 93-94-95 4.3 vortex its the spider injection located inside the plenum the part costs between $250 to 400 i had to replace on girlfreinds 94 blazer. ifound one o ebay for $100

remove the oxigen sensor and drive it, if it get so much better power then you catalitic at exaust is restricted and have to be replace, note: by driving whit 02 sensor remove it will make a lot of noise don't be worry this is normal just make sure nothing overheat by the 02 sensor hole