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Discussion Starter #1
the lady just bought it used. it is a 96 GMC with a 5.7 and 4x4. it was regularly serviced at a repair shop in spangle. we have run two cans of seafoam through it because it sat for two years. the only check engine light that came on was for low voltage to the o2 sensors. they were both changed, didn't help. battery voltage is up where it is supposed to be. the fuel pressure was checked and with the key on engine not running it was 55 psi until you turned the key off then it dropped to zero. with the engine running it was between 60 and 65 regardless of throttle position. the trans is starting to slip a little and when you put it in reverse it hesitates then slams into gear the fluid is up to full. it is getting great gas mileage. a tune-up was just done just before it was set aside. everything tune-up wise looks new. there must be a bad sensor or pressure regulator that is bad or something. it is getting frustrating.
 

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Did you check both banks of O2 sensors or was it just one side?
 

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And, do you recall the O2 code(s)?
 

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when key is turned off and the fuel pressure drops most likely the injectors are leaking.
1996 GM engines the fuel spec is 5% alcohol .. now it is 10% so fuel does damage these 1996 Injectors...when it sits...
when I put my 96 Impala to sleep in winter I use MMO and fuel stabilizer to protect the complete fuel system... alcohol kills these fuel systems.. also pull out the fuel pump see whats up..
 

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Discussion Starter #5
i checked both o2 sensors, it said low voltage to the sensors. it doesn't like low speed especially in gear, trans shifts funny as well.
 

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I understand that. However there are four of them. Two ahead and two after the cats.
Did you take a volt meter to the plug to check for 12V to ground on each one?
 

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Discussion Starter #7
i didn't know there was four i can only see two maybe it was modified there are aftermarket cats on there.
 

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You may have 3, one in front of each cat and one after the Y pipe.
 

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Discussion Starter #9
i will look again as soon as i can get tol her house but i only saw two o2 sensors so somebody has been modifying.
 
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