1998 GTP Misfiring problem, and need some troubleshooting

[2000GreySSEi]

My uncle has a 98 GTP, and it has some problems with misfiring, and hard starts. Here are his codes:

P0303: Cylinder 3 Misfire
P0336: Crankshaft Position Sensor A Circuit Range/Performance
P0420: Catalyst System Efficiency Below Threshold (Bank 1)
P0440: Evaporative Emission Control System
P1404: EGR Valve
Here are my suggestions:

P0303: Checked Fuel, and spark both fine. My guess is it is caused by the CKP sensor code.

P0336: I logged it the misfire count after driving 10 minutes:

Cylinder 1: 1
Cylinder 2: 4
Cylinder 3: 2015
Cylinder 4: 400
Cylinder 5: 12
Cylinder 6: 1

I think the Crankshaft positioning sensor is causes the missing, but its really taking a toll on cylinder 3.



P0420=Clogged cat: When he bought the car, I noticed when I gave it full throttle. The rpms wouldn't go past 4k, and it stuttered and made some wierd noises. I thinking the cat it clogged nearly shut.


My Scenario: The CKP sensor went out. Thus causing these misfires. The misfires heated the cat up, thus making it kill itself.

What you guy think. Is my diagnostics right?

[swampthing]

I would say get the crank sensor changed first and see what the misfires do. If the cat really is plugged you should try to talk him into getting a downpipe/cat from zzp

[2000GreySSEi]

Yea I'm definetly going to tell him about that.

[00Beast]

First replace the cat. Then look at the misfires, and check the crank sensor replaced.

A ZZP DP wouldn't be a bad idea, or at the very least a u-bend delete...