oil pressure question

my friend has a 91 s-10 blazer all wheel drive. the gauges show that his oil pressure is a little below normal but gets worse as the engine heats up (exspecially at lower rpms) now there is only 2 bars when you start it up and after a few minutes the warning light flashes. i thought it was the oil pump but a few people said it could be the crank bearings or some sort of assembly piece. any info would be helpfull before i have to try to repair it with a hit-or-miss technique. thanks

before you assume its the oil pump make sure you check the oil pressure sensor.
you will need to find the oil pressure sensor and unscrew it. you will need a pressure gauge (that is capable to read at least 100psi) with the correct fitting to screw in the sensor's place. start the engine and the cold start pressure reading should be high (50-60psi) then it will drop as it warms up. idle pressure when warm can be around 20-30psi. also if your actually losing pressure you will notice a taping noise from the valve lifters as they need oil pressure to work. if you dont hear tapping noise and the oil pressures are fine, then its safe to assume the sensor is bad. if you have noise and a loss of oil pressure well then you might as well rebuild the motor because a lot of things can cause oil pressure loss. most people assume its the oil pump but worn bearings and check valves in the oiling system can also be a cause.
good luck!

thanks alot. i don't have a service manual on it. do you know where the oil pressure sensor is located at so i can hook up a pressure gauge on a 4.3-(not possitive), v-6

check in the back of the motor next to the distributor. you should see a 1 wire sensor screwed into the block.