Japscrap_96

I own a 96 240sx manual with 193k miles on it. I'm having a bery specific problem with it. When I first start the car it drives awesome for the first 30-50 mins, after that it begins to lose power. For example, if I come to red light and want to take off the car barely moves (no pull) but the RPM goes up. This same thing happens on second and third. It takes really long to catch speed. Even if I floor it!
It's alsmost as if the clutch was slipping. Two weeks a go a technician friend of mine replaced the clutch for me, but the problem didn't go away. We scanned the car and got 5 codes (p0304, p1447, p0446, p0440, and p0325) The most important ones where misfire on cylinder 4 and knock sensor. So last night I went ahead and did a tune up to the car. I bought NGK plugs and wires, new cap and rotor, and bought a knock sensor. The misfire went away, the cap was cracked. I drove the car that night for an hour and 10 mins (the longest its lasted without losing 50% power or so) I called my buddy and he said it could be an O2 sensor or a coolant temp sensor. So I bought those two and put them in, I also went from mid grade to premium gas. The car drove like a dream. I even did some skids. An hour into the fun drive the car lost power and was barely moving. Now I'm here sitting trying to figure out what's wrong with the car. I would really appreciate it if you could help me out. Thank you so much.

russianphil18

if the coolant temp is normal then its not getting hot. more than 20 mins means your car is at full operating condition coolant temp and oil temp wise.

your buddy suggested a coolant temp and 02 sensor because if those are reading wrong your ecu will compensate by either giving more fuel or restricting fuel depending on the condition it thinks the engine is in based off the sensor.

I would suggest getting more data. get AFR and battery level when the car does it again. Dont just throw parts at the car. figure out what is really going on.

This will tell you:
- if it is dumping extra fuel it does not need - points in one direction
- if its not dumping enough fuel - points in another direction
- battery voltage is low - not enough power to the fuel pump to sustain the proper fuel pressure and the ecu has no idea of that...AFR will change aswell...as the rpms climb slowly the battery will charge.

Japscrap_96

All of what you're saying makes perfect sense. I decided to put in those parts because I could afford them plus the car benefits a little. I'm go ahead and try what you've suggested. I continued my search and some one at another forum told me that I could also have a back pressure issue since the car had a misfire for quite a while. It makes perfect sense, the catalytic could be clogged and full of crap. I'm also going to straight pipe the car. I was going to do it anyways. Thank your for your help.

russianphil18

catalytic converters normally get hot enough to clean themselves so if you drove it a lil after you fixed the misfire it shouldn't be clogged. but there is always a chance.

anyway good luck, and post your solution later or questions if your still stuck