Buick Rainier - multiple random misfires

Last post on Sep 22, 2009 at 10:47 AM

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#1 of 1 2004 Buick Rainier - multiple random misfires by justint Sep 22, 2009 (10:47 am)
I have a 2004 Buick Rainier CXL AWD with 5.3L engine and 70k miles. The vehicle is experiencing multiple random misfires under certain repeatable conditions. The typical condition is that I start the car cold, drive downhill to town (<3 miles) and stop somewhere to run errands. After 5-15 minutes I start the car and by the time I get out of the parking lot it is misfiring so badly it seems like it will stall. Specifically: about 2 minutes after a warm start when engine rpm is <1000, transmission in drive, A/C engaged, multiple misfires occur and P0300 and P0171 are sometimes set. Freeze Frame data indicates Closed Loop status, among other things. After about 2 minutes of misfiring at or near idle, the engine smooths out and does not appear to misfire again no matter how long that drive cycle lasts. During this 2 minute window of misfiring, the engine smooths out if I rev the it above about 1500 rpm, but misfires again when the engine idles down. This same symptom appears on cold starts under heavier engine load when I drive it uphill from a cold start, so I'm assuming it is in Open Loop status, but don't have FF data to prove it. Additional information: This problem began shortly after the fuel sender assembly was replaced under Special Policy 07076A. The Fuel Tank Pressure Sensor (P/N 16238399) was also replaced during the repair. The dealership insists nothing in that repair could be causing this symptom, but I wanted to include the info here for a complete picture. Also, TID/CID 0A 0A is out of spec with a value of 0.000 (Evap System Monitor, Small Leak Test.) I would appreciate any assistance because the dealer has not been able to figure this out and the diagnostic costs are escalating quickly. I have a scantool If you need more OBDII info. Thanks in advance.

#1 of 1: 2004 Buick Rainier - multiple random misfires by justint; Sep 22, 2009 (10:47 am)

I have a 2004 Buick Rainier CXL AWD with 5.3L engine and 70k miles. The vehicle is experiencing multiple random misfires under certain repeatable conditions. The typical condition is that I start the car cold, drive downhill to town (<3 miles) and stop somewhere to run errands. After 5-15 minutes I start the car and by the time I get out of the parking lot it is misfiring so badly it seems like it will stall. Specifically: about 2 minutes after a warm start when engine rpm is <1000, transmission in drive, A/C engaged, multiple misfires occur and P0300 and P0171 are sometimes set. Freeze Frame data indicates Closed Loop status, among other things. After about 2 minutes of misfiring at or near idle, the engine smooths out and does not appear to misfire again no matter how long that drive cycle lasts. During this 2 minute window of misfiring, the engine smooths out if I rev the it above about 1500 rpm, but misfires again when the engine idles down. This same symptom appears on cold starts under heavier engine load when I drive it uphill from a cold start, so I'm assuming it is in Open Loop status, but don't have FF data to prove it. Additional information: This problem began shortly after the fuel sender assembly was replaced under Special Policy 07076A. The Fuel Tank Pressure Sensor (P/N 16238399) was also replaced during the repair. The dealership insists nothing in that repair could be causing this symptom, but I wanted to include the info here for a complete picture. Also, TID/CID 0A 0A is out of spec with a value of 0.000 (Evap System Monitor, Small Leak Test.) I would appreciate any assistance because the dealer has not been able to figure this out and the diagnostic costs are escalating quickly. I have a scantool If you need more OBDII info. Thanks in advance.