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1998 GTP Misfiring problem, and need some troubleshooting

FlaminWhite97GTP

FlaminWhite97GTP

New member
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?
 


Have you checked to make sure ignition coils are not bad I had a couple bad on my 2001 gtp and I had 3rd cylinder misfireing?
 
move the coils around and see if the misfire moves with it. if it does then you know the coil is the prob.

sounds like you need to check that crank sensor too.
 
When was the last time the plugs/wires were changed? That could account for the misfires. These coils are known to be pretty solid but they can cause issues. The ICM (Ignition Control Module) that the coils sit on (the large metal rectangle under them) can also cause issues. Also, that many misfires will destroy a cat converter so be gentle on it.

The EGR codes are probably related to a bad purge valve solenoid or possibly a leak at the EGR. The flexible tube on the EGR like to break in the accordian sections.

If the Crankshaft position sensor went completely out the car would not run due to it not feeding the ECM the info it needs in relation to cylinder postion, firing order, etc... If the car still runs but you notice the tach dropping to zero before it dies out then that would be a tell-tale sign of a bad Crank sensor. FYI- You have to remove the harmonic balancer to change out the crank sensor. It is located behind it on the right side.

The P0420 could just be a bad O2 sensor. If you suspect a clogged cat then you could test it by either removing the O2 sensor and see if it runs better, or drop the exhaust off of it and test. If all is well then your cat is clogged.

The fact that it will not go past 4K at WOT indicates that the ECM is pulling spark/fuel in order to keep you from blowing up the motor (chipped piston, etc). It is doing this on purpose. Do not do any more WOT runs until you can get these misfires fixed and cat checked out for being clogged or your uncle may be looking for a new longblock.
 
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