2001 cavalier cylinder 3 misfire. changed injector, computer, map sensor. Still have cylinder 3 misfire

You need to figure out what's causing the miss first. If the code was 302 or 303 the cylinder is not producing power, but the reason is a mystery. It could be ignition, the injector, or a compression problem. Since the cylinder problem changed, I doubt its compression.
The code for the map sensor could be something other than the sensor too.

Dirty fuel injectors. Computer will show misfire on the cylinders that are malfunctioning. If injector cleaner in tank won't clean them, pull them all out and have a professional take them apart and cleaned. Each injector has a screen in it that can get plugged up. Think about Bro, all other stuff has been renewed.

If you are getting a misfire from cylinder #3 your check engine light should come on and read this code: P0303 which is Cylinder 3 Misfire Detected. Below I have listed what causes this and a few solutions that may help you out.

Causes:
- Improper spark plug at cylinder #3
- Insufficient compression at cylinder #3
- Incorrect fuel pressure
- The injector circuit is open or shorted at cylinder #3
- Fuel injector #3 may be faulty

Solutions:
- Perform Injector Service
- Replace Spark Plug #3
- Replace Injector #3
- Replace Ignition Coil #3

Failure-to-start scenarios are often an issue of "fuel or spark?"

To check fuel pump, install a fuel pressure gauge on the Shrader valve connector on the
fuel rail, reading ???? - I couldn't find the spec for nominal fuel pressure.....

One good source of diagnostic info is your car's computer - commect an OBD-II code
reader to your car's OBD-II port and ask the car what it thinks it wrong - its capable of
posting 100s of possible error codes, any number of which would/could implicate a fuel
system component. Here a (very) short list of possible computer codes your car's computer
may currently be posting:

error code meaning
--------------- -------------
P0107 MAP (manifold absolute pressure) sensor - low input (to computer)
P0108 MAP (manifold absolute pressure) sensor - high input (to computer)
P0122 TP (throttle position) sensor - low input (to computer)
P0123 TP (throttle position) sensor - high input (to computer)
P0171 fuel system lean
P0172 fuel system rich
P0201 fuel injector 1 control circuit malfunction
P0202 fuel injector 2 control circuit malfunction
P0203 fuel injector 3 control circuit malfunction
P0204 fuel injector 4 control circuit malfunction
P0300 multiple engine misfire detected
P0301 cylinder 1 misfire detected
P0302 cylinder 2 misfire detected
P0303 cylinder 3 misfire detected
P0304 cylinder 4 misfire detected
P0336 CPS (crankshaft position sensor) range/performance
P06xx control module (computer) failure


Possible bad parts:
TP (throttle position) sensor - Duralast TPS172 $51.99 at www.autozone.com

Fuel pressure regulator:
www.autozone.com/autozone/regairinfo/repairguide/repairGuideContent.jsp?pageId=0996b43f8036e816

Fuel Pump:
www.autozone.com/autozone/repairinfo/repairguide/repairGuideContect.jsp?pageId=0996b43f8036e7c7

Fuel Filter:
www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?pageId=0996b43f8036e787

Fuel rail (supply manifold) and fuel injectors:
www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?pageId=0996b43f8036e7a0

Could also be dying fuel pump relay - Duralast 19264 $14.99 at www.autozone.com.
I don't work for Autozone.com - just convenient info for some cars.

Autozone.com will expect you to register (free) to access their repair guide database (which has pictures - especially helpful for finding sensors).

did you replace only one spark plug? that can cause issues because of differences in resistances between cylinders. also, did the map code stay off after replacing
?

1. Freeze Powertrain Control Module (PCM) and see if the problem can be duplicated.

2. Wiggle tug test wiring for #2 injector.

3. Scope the #2 injector for a glitch when the misfire happens. 1. Test for the Exhaust Gas Recirculation (EGR)/coolant adapter gasket leaking EGR gases past the gasket.

2. Connect a vacuum pump to the MAP sensor, block the vacuum source, reset fuel trims, start the engine and add typical vacuum to the MAP sensor and check operation.

3. Test the spark output with 2 High Energy Ignition (HEI) testers, at 25 KV air gap each, at the spark plug wires to ground at wires 2 and 3, then 1 and 4 at cranking speed and engine running.

4. Test the fuel injector pulse width at the injectors compared to the scanner data.

5. Disconnect the O2 sensor, reset the fuel trims, test the system operation in open loop, test injector pulse width. Compare to the closed loop operation injector pulse width and engine operation.

6. Test the Powertrain Control Module (PCM) powers and grounds during the problem.

NO to the MAF Sensor Question, and Spark Plug Wires Or BOOT Will Cause Missfire. As For Mass Air Flow Sensor Easy Check is to Dissconnect it While Engine is Running And If ENGINE SMOOTHES OUT The Sensor is Bad

One thing to check is the fuel pressure regulator.
If the diaphram is leaking it will cause gas to be pulled into the vacuum system causing lots of white smoke and extreme rough running.

Replace the coil pack.

Replace the coil pack..