Engine Performance problem
2003 Pontiac Grand Prix 6 cyl Front Wheel Drive Automatic 120000 miles
I've been battling this problem for the better part of two years and everything I have tried has yielded no positive results. The issue is noticed with both driveability symptoms and scan data.
-Engine bogs down in situations such as passing on the highway or going uphill. Situations with a sudden increase in throttle, generally before the engine attempts to shift into the next gear.
-after the vehicle has been sitting for an extended amount of time, the engine will take noticeably longer to crank before starting.
-Idle vibration. The vehicle has an idle vibration, most noticeably at the 1000 RPM range when held at this mark with the throttle.
-Idle "missing". I have an aftermarket exhaust system and when listing to the exhaust there are blips of what sounds like a miss. However, this is not picked up with a scantool as a miss. This "miss" can be felt as a slight vibration in the seat.
Scan Data Symptoms:
-Knock retard relative to boost. High amounts of knock retard are presented when accelerating and most noticeably when boost is applied.
-P0420 Code set. Occasionaly I will receive a catalyst below efficiency code. It is very rarely that this code is set, and is not consistent with the above symptoms.
Repairs/Replacements to correct issue:
-Spark Plugs Replaced (ACDelco)
-Spark Plug wires replaced (ACDelco)
-Iginition Control Module replaced (ACDelco)
-Fuel Injectors replaced (Reconditioned ACDelco)
-Fuel Pressure regulator replaced (ACDelco)
-Fuel Pump Assembly replaced (Delphi)
-Fuel Filter Replaced (ACDelco)
-Front 02 sensor replaced (Denso)
-Rear Exhaust manifold replaced (Ported ACDelco)
-Catalytic converter replaced (Magnaflow)
-PCV valve replaced (ACDelco)
-IAT Sensor replaced (ACDelco)
-Lower Intake Manifold gasket replaced (ACDelco Revised Aluminum)
Other previously Installed Parts Status:
-Downpipe (Aftermarket 2.5" with bend restriction after cat straightened)
-Supercharger Pulley (Stock)
-Powertrain Control Module (Stock)
-MAF Sensor (Used Stock)
-Fuel Pressure Test (at Idle)=Passed
-Fuel Injector Drop Test=Passed
-No Vacuum leaks found
Recent Vehicle Scans:
-Wide Open Throttle
This problem at first seemed to have many possibilities and could be easily diagnosed, however after many replacements of what seemed to be the faulty parts, the problem has gotten more and more frustrating. I have tried for the duration of this problem to seek help on forums specific to my vehicle with little success, or suggestions that I have already tried (hence the detailed lists of where I currently stand)
have the same problem?
Saturday, June 19th, 2010 AT 2:56 PM