Engine Mechanical problem
1995 Nissan Sentra 4 cyl Front Wheel Drive Manual 200000 miles
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I am a shade tree mechanic but this problem has me baffled. My wife comes home the other day and says when she left work the car barely wanted to crank over so I am thinking it’s the battery since I replaced the alternator 2 years prior. I get my volt meter out and check the batter and sure enough 11.75 volts then I start the car and it the same 11.75 voltage so I go to check my alternator and notice it’s belt was gone so I replaced the belt which connects the Alternator, A/C Compressor & Crank then start the car and now I am getting 13.5 volts which is great but now a new problem as emerged. At an idle (aprox. 800 rpm’s) there is no trouble and the car idles fine but if you try to give it the least amount of gas (around 1500 rpm’s or above) the car rages up and down on its RPM'S when you are keeping the accelerator constant, sounds like the rev/rpm limiter is kicking in why to early. Check the fuel supply and its PSI is constant and accurate. There is no codes and no prior history with the symptom with this car. I wouldn’t think the electrical ignition module, the pick-up coil or O2 sensor could go out just by replacing an Alt. belt. Any thoughts would greatly help.

What is the alt output off idle? use your meter to see if it is throwing a/c current, this will mess with the ecm

2CarPro Jack wrote:

What is the alt output off idle? use your meter to see if it is throwing a/c current, this will mess with the ecm

UPDATE: Prior to receiving this answer I unplugged the neg battery post and also the 02 Sensor and wait a couple of hours, after returning I plug up the neg battery post and started the car, again the 02 Sensor was disconnected. It runs like a champ so I shortly plugged up the 02 Sensor back and still run like a champ. I test drove the car all over then waited till the next morning leaving every thing connected and again no trouble running at all. I am guessing the ECM just needed to be cleared and waiting the few hours with both disconnected done the trick. What are your thoughts? Thanks

I guess that s possible. needed a little re-learn time