I have a 1998 chevy venture mini van...... Seams to be miss firing on two cylinders we replaced the crankshaft sensor... The computer is showing po300 and po 336... Any ideas thank you

First have the computer scanned . Most part houses will do it for free. The miss fire codes will tell you where to look. It can identify which cylinders are miss firing or not firing at all. Identify the bad cylinders and pull the spark plugs and run a compression test on them to make sure they are ok. No compression means a problem like a burnt valve. Make sure that the firing order of the plugs are correct.

If your talking the 02 sensor, it's in the exhaust. Bank one is the bank with the number 1 cylinder and sensor 1 is the first 02 sensor.
The number 1 cylinder shows to be located in the rear bank. If you only have two 02 sensors, that would be one before the cat and one after.

you might need to get a shade tree technician to flash to computer you can even buy the program to go on your laptop to flash the computer yourself

I guess I should start by saying the code did not say the sensor was bad. It probably said the sensor signal was out of range.
If replacing the sensor fixed the code but the engine still runs rough and stalls, it could be a leaking injector or a problem with the throttle body.
You would need to know which cylinder is causing the miss.

Why would you change a crank sensor

It failed a test?

How was it tested?

No parts get changed just for something to do

incorrect firing order for the plug leads
low fuel pressure

what motor do you have in it?

most any sensor going bad can cause the check engine light to come on,try disconnecting the posative battery cable for 15 seconds ,then put it back on,will reset the codes, or take it to auto zone,they will test your computer for codes at no charge to you.i had a venture van my was ox. sensor. thanks robert b.

the 2 codes are

P0134 02 Sensor Circuit no activity Detected (bank 1 sensor 1)
first check your fuses check the wiring to the sensor(the sensor is on the exhaust in front of the engine-open the hood and look down) if the fuses and the wiring look good replace the O2 sensor there are 2 types of sensors original equipment(oe) style and universal the oe style has a connector you just plug in, the universal you have to hard wire in

the 2nd code is Mass Air Flow (MAF) Circuit Low Input
check the wireing, make shure theres a good connections
you said that you already replaced this sensor so im going to recomend that you go after the other code first

deal with the oxygen sensor then reset the computer and see what codes come back

You should really have the van scaned before you put any more parts on it. Autozone will scan it for free. You could spend alot of money just putting parts on it. If you can come up with a code/DTC for your problem then let me know and I will be better able to help you. Good Luck