Car lacks power

I have a 02 nissan sentra gxe with 100k miles. I got it used when it had 70k miles on it. It is very reliable and gives me great milage. However I noticed when I drive uphill the car lacks power and is unable to pick up speed. If I drive too long uphill at high speed the engine starts getting hot and I am forced to slow down.

I am a Automotive Technology student at a Community college and would like to diagnose this problem myself.

I changed the spark plugs recently and that did not slove the problem. I was suspecting it might be the fuel filter. However on a 02 nissan sentra it is in the gas tank and is not replacable.

It can also be the oxygen sensor. However I thought the car engine lights will indicate when it is time to replace the oxygen sensor.

Does any one have any suggestions ? Thanking you in advance.

You may have 2 problems, low power and overheating.
Overheating could be clogged raidiator, hose closeing up,thermastat, waterpump getting wore or convertor getting cloged causing backpressure witch can lead to overheating.
When was timing belt replaced? If it is wore it can get slack in it and timing can be off.
Now a days when a 100000 mi car starts to spark knock because of carbon build up computer retardes timing to stop spark knock witch hurts power.If that is the case put in high test for 2 tanks and it will make a huge difference.
Also make sure intake and filter is not clogged.

The engine only overheats when there is not enogh power. On a flat road I do not see any problem and the car runs fine. In a 02 sentra i dont think the timing belt needs replacement. Atleast the owners manual does not say so.
The previous owner did not take proper care of the car. When I first got it there was cigeratte burns and coffee spills all over. Since I got it 3 years ago I started taking good care of it.

Ok, so it’s an 02, but it has 100K on the clock! Unless you know the T-Belt was already changed you had better do that now before it breaks (expensive repair). And yes, that could cause the timing to jump and make it run poorly and make more heat that normal (bad). The manual should say something like “every 80k miles or 5 years, whichever comes first”. You would be over on both accounts.

When you drive uphill the engine has to work harder, making more heat which the radiator has to get rid off. If your fluid is at the correct level, I’d guess you have something blocking the coolant loop. That could be the radiator itself (clogged up), bad water pump (not pushing much water), etc. Have it checked out. If its not that, make sure nothing is blocking airflow in and out of the radiator - small airflow = little cooling.

If you suspect that the fuel pump or fuel pressure is the culprit, put a gauge on the fuel log feeding the injectors and see if the pressure holds up as the engine is under power. Also check that the catalytic converter is not restricted by putting a gauge in the upstream O2 sensor bung and running the engine under power.

Usually the O2 sensor will fail by not producing a voltage which will make the fuel trim rich. Also under hard acceleration the ECM commands a richer open loop injector pulse width which does not take the O2 readings into consideration. Depending on the programing, the calculation may go into closed loop (O2 sensor reading taken into consideration) at WOT but usually a rich mixture is prefered as it reduces the chance of detonation.

Hope this helps. Let us know what you find out.

Clogged converter