96 corsica acceleration hesitation


walnuts
08-10-2008, 02:54 PM
Good afternoon

I have a 96 3.1 lt corsica that has a hesitaion problem on acceleration . I have been through the fuel system twice already and have changed the fuel pump and the throttle positioning sensor but the hesitation is still there . I had a fuel pressure gauge on while driving the car and when it was hesitating it was pushing the pressure UP from 40 psi to 49 psi , so it tells me that is flooding itself when it starts hesitating . The error coding keeps showing an evap error but I can not find anything wrong with the map sensor , the mass air flow (this was also changed by the way ) , or any of the vacuum lines . With the current cost of fuel being so high any help fixing this would be greatly appreciated . Thanks in Advance

DaleReynolds24
02-27-2009, 01:29 PM
Hey walnuts. Possibly a bad o2 sensor could be the problem. The o2 sensor measures the amount of gas and stuff in the exhaust and the way your telling the problem, it might be the sensor is just faulty and its telling the CPU to give the car more gas because its sensing that the exhaust mixture is too lean. I do not know 100% for sure, but it could be a faulty o2 sensor.

I know its been a while since you posted and maybe its been fixed, but glad I could offer some help!

freebirdjr
04-02-2009, 10:06 AM
I had the same acceleration hesitation with my 3.1 96'. We were having cadilic convertor problems so we cut it out and replaced it with a straight tube muffler and cut the O2 sensor. Mechanic friend said that it's normal for the o2 to want to compensate for the amount of fuel going to the engine. Thus it gives it more rich fuel making you eat up gas, but it wasn't hesitating anymore. Yee Haw, right! Hope you got it fixed! Follow up?

manicmechanix
04-04-2009, 03:12 PM
Sounds like to me the OBD II is telling you where your problem is, the EVAP system. Have you really ran the proper diagnostic on the EVAP? 49 psi fuel pressure seems a little high, but it's normal for the fuel pressure to rise when you open the throttle and vacuum drops. Maybe the EVAP fault is really killing your vacuum causing the fuel pressure to rise more. Of course higher fuel pressure means the injectors would deliver more fuel for a given IPW (injector pulse width), but IPW is varied by the PCM to compesate for that anyway, especially under closed loop. If the IPW wasn't low and was high you would be getting a richer fuel mixture and fuel pressure would likely drop some. But a higher fuel pressure in its self doesn't mean the engine is necessarily getting a richer mixture.

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