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Old 09-02-2016, 10:12 AM   #1
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Default Throwing codes PO300 PO420 PO507

Figured I would start with plugs and maybe wires for the po300 misfire.. my girlfriends car cuts out badly when you first start it and periodically while your driving.. when first started it struggles to stay running then after about 20 to 30 seconds it revs to about 3000 rpm then smooths out...
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Old 09-02-2016, 11:30 AM   #2
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Might also want to check fuel pressure and check for vacuum leaks.
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Old 09-03-2016, 02:53 PM   #3
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You can check for vacuum leaks by spraying carburetor cleaner around the top of the engine(upper and lower intake, throttle body, vacuum lines) and if it revs up then you have found your leak!
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Old 09-04-2016, 03:14 AM   #4
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What model and engine is this?

It may also be wise to check the fuel pressure regulator to confirm that fuel is not coming in through the vacuum line side.
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Old 09-04-2016, 12:36 PM   #5
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Losing coolant?
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Old 09-05-2016, 11:47 PM   #6
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So I changed the spark plugs they were in dire need didn't change anything and in the process I found a vacuum leak. The rubber connector that connects two different sized vacuum lines to the side of throttle body couldn't find a replacement so for now I used f.r. electrical tape still no change.. I took the car about 180 miles to the illinois river this weekend then thought to maybe unhook battery for a couple hours to reset computer.. it now runs worse than when I started... I plan to check fuel pressure regulator tomorrow and check for more vacuum leaks with the carb cleaner method thanks for the input guys keep it coming.. I'll update tomorrow.. oh this is a 2000 buick lesabre with the 3.8 by the way
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Old 09-05-2016, 11:49 PM   #7
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Losing coolant?
No not losing coolant.. just flushed entire system to do away with dex cool crap. All good there
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Old 09-27-2016, 05:42 AM   #8
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Quote:
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So I changed the spark plugs they were in dire need didn't change anything and in the process I found a vacuum leak. The rubber connector that connects two different sized vacuum lines to the side of throttle body couldn't find a replacement so for now I used f.r. electrical tape still no change.. I took the car about 180 miles to the illinois river this weekend then thought to maybe unhook battery for a couple hours to reset computer.. it now runs worse than when I started... I plan to check fuel pressure regulator tomorrow and check for more vacuum leaks with the carb cleaner method thanks for the input guys keep it coming.. I'll update tomorrow.. oh this is a 2000 buick lesabre with the 3.8 by the way
You have a vacuum leak at the vacuum lines that can NOT be fixed with electrical tape. Buy a can of carb cleaner and check for leaks. The vacuum lines and tee connectors DO get brittle and break on a car this old. Go to a good parts store and have someone knowledgeable come out to the parking lot and look at it. Vacuum tubing and tee connectors are cheap.
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