Sputter under heavy load

I have a 99 GTP with 88k. Intermittently when the car is under heavy load, (flooring it from a stop usually), it seems to sputter, or skip a beat if you will, at about half boost. I changed the plugs and wires and the problem did improve but it's still occuring. Any advice?

check fuel pressure yet?

Fuel filter also

No, how do I check the fuel pressure?

Cuts Out, Misses
Checks
Action

DEFINITION: Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases.

Preliminary
• Refer to Powertrain On Board Diagnostic (OBD) System Check .

• Refer to Intermittent Conditions .

• Search for bulletins.

Fuel System
• Check system fuel pressure. Refer to Fuel System Pressure Test .

• Check the fuel injectors. Refer to Fuel Injector Balance Test , Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) or Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F) .

• Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• Check items which can cause an engine to run rich (long term fuel trim significantly in the negative range). Refer to Diagnostic Aids for DTC P0172.

• Check items that can cause an engine to run lean (long term fuel trim significantly in the positive range). Refer to Diagnostic Aids for DTC P0171.

• Check for fuel in the Fuel Pressure Regulator vacuum hose.

Sensor/System
Check for conditions which cause an incorrect idle speed.
• Throttle body tampering, excessive deposits, or damage. Refer to Fuel Metering System Component Description .

• Restricted air intake system.

• Large vacuum leak.

Check the TP Sensor and related circuit wiring. Refer to DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage .
Check the EGR system for proper operation. Refer to Exhaust Gas Recirculation (EGR) System Description .
Check the PCV Valve for proper operation. Refer to Crankcase Ventilation System Description .
Check the Transaxle Range Switch input with the vehicle in drive and the gear selector in drive or overdrive.
Check the following for damage:
• Bent harmonic balancer interrupter rings.

• Damaged Crankshaft Position Sensor.

Ignition System
• Check for proper ignition voltage output using the following steps:

- Clip the J 26792 spark tester to engine ground.

- Connect one end of a spark plug wire to the J 26792 spark tester; leave the other end of the spark plug wire to the coil being tested.

- Connect one end of another spark plug wire to the other coil tower; connect the other end of the spark plug wire to ground.

- Crank the engine while observing the J 26792 spark tester; a crisp blue spark should be observed.

- Repeat the above steps for each coil.

• If adequate spark is not present at the coil(s), check for the following conditions:

- Coil(s) -- Cracks, carbon tracking/arcing, or a resistance value outside the specified range.

Coil Resistance
5000 - 7000 ohms (5K - 7K ohms)

- Spark Plug wires -- Signs of arcing/cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range.

Spark Plug Wire Resistance
600ohms per foot (1 968ohms per meter).


Important: : Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem. Ignition components will arc to ground when a secondary component is faulty.


- Defective module.

- Ignition System Wiring -- Loose ignition module feed or ground connection, or damaged system wiring.

• Remove spark plugs and check for the following:

- Fouled plugs

- Cracks

- Wear

- Improper gap

- Burned or damaged electrodes

- Improper heat range or reach

• If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

• Check for the following intermittent ignition system conditions:

- Intermittent CKP 24X Signal.

- Intermittent ignition feed circuit or sensor ground circuit to the crankshaft position sensor or the camshaft position sensor.

- Intermittent 3X reference signal.

- Intermittent camshaft position signal

Engine Mechanical
• Check engine mechanical for the following:

- Check compression. Refer to

- Sticking or leaking valves.

- Worn camshaft lobe(s).

- Valve timing.

- Bent push rods.

- Worn rocker arms.

- Broken valve springs.

- Excessive oil in combustion chamber-Leaking valve seals.

- Low cylinder compression.

• For incorrect basic engine parts. Inspect the following:

- Camshaft

- Cylinder heads

- Pistons, etc.

• Refer to Base Engine Misfire Diagnosis .

Additional Checks
• Check exhaust system for possible restrictions. Check for the following:

- Inspect exhaust system for damaged or collapsed pipes.

- Inspect mufflers for heat distress or possible internal failure.

- For possible plugged Three-Way catalytic converter. Refer to Restricted Exhaust System Check and Exhaust Leakage - Not OBD II .

• An engine miss condition can be caused by Electromagnetic Interference (EMI) on the reference circuit. EMI can usually be detected by monitoring engine RPM with a scan tool. A sudden increase in RPM with little change in actual engine RPM change, indicates EMI is present. If a problem exists, check routing of secondary ignition wires, high voltage components (Near Ignition Control circuits).

• Check for intake and exhaust manifold passages for casting flash. Refer to Base Engine Misfire Diagnosis .

• Check for faulty motor mounts. Refer to Base Engine Misfire Diagnosis .