First of all, I would like to apologize for posting this question here since this forum is for honda accords and my question is regarding Nissan Altima, but experts on this forum have helped me and guided me extensively every time I had any trouble or question regarding my 1994 Honda Accord. I believe that my question is pretty general and you experts will help me solve it. However, I understand if moderators decide to delete this post as irrelevant to the forum.

My 1997 nissan Altima (136K miles) seems to have problems accelerating. On regular flat roads, it accelerates perfectly normal upto 60-70mph, however, on roads with a slight up slope or bridges, as I try to accelerate to keep the speed constant or accelerate, the engine begins to rev faster but the car does not accelerate, instead will struggle to speed or slow down a bit. I tried driving up a bridge using cruise control once to see what happens. Turns out the car still struggles a lot and RPM goes very close to red region.

I recently had the AutoZone ppl read the Check Engine Light code read for me. It is P0240: Catalyst System Efficiency Below Threshold (Bank 1). I had the muffler and mid-pipe replaced 2 years ago since it had a hole in it, which was making the car run very loud.

So is the acceleration problem associated with this error code or it is the transmission or tranny fluid?

BTW, a couple years ago, the car stalled often and a mechanic at the Nissan dealership said the fuel pump must have conked out. So it was replaced. Also, during the recent oil change, the air filter also was changed.

any ideas appreciated.

 

Initial throttle problem problem will be the TPS. that controls the throttle body to open to allow air to the motor thus resulting in combustion and acceleration.

As far as the OBDII code: It is your O2 sensor bank 1.(connected to the exhaust manifold).

 

Engine speed increasing w/o acceleration suggests a problem w/ torque converter slipping or drive clutches slipping. I assume this is an automatic. Make sure you have adequate fluid in the transmission. I would also check for any OBD2 transmission codes that might be presented.

Code P0420 for catalyst system efficiency below threshold will not affect engine performance. It only means the catalytic converter is not performing as designed.

good luck

 

Severe loss of power together with P0420 - an outside chance of the catalyst plugging up? Dont forget to check the other suggestions, but just add this possibility to the list.

At least with Honda, by 1998 the ECU was pretty good at telling the difference between a bad O2 sensor vs a bad catalyst.

 

Repeating above recommendations, but check the tranny fluid level. If good, your clutch is going bad or if auto, TqCon or frictions are going bad.

 

assuming its a manual...to check if its tranny...try accelerating hard in too high a gear...say, 5th gear at 35mph. if it does the same thing, i'd say the clutch is slipping.

 

Thanks for all the replies. I will post again with the transmission fluid level. I am sorry I forgot to mention it is an automatic transmission.
As far as the code is concerned, will replacing the O2 sensor help or the catalytic converter needs to be replaced? I may put this on the back burner if it is not affecting the engine performance.

 

The transmission has problems and there may be transmission codes present w/ that level of slippage.

Is this by any chance a CVT (continuous variable gear ratio - no shifts). I know Nissan makes these trans, but don't know much else.

P0420 is a difficult problem to resolve. It can be caused by damaged catalytic converter, exhaust system leaks before converter, faulty primary (ahead of converter) O2 sensor, and faulty secondary or rear (aft of converter) sensor. Monitoring the rear O2 sensor performance w/ a good scanner is best way to diagnose problem. Cataltyic converter is too expensive to replace on a guess.

good luck

 

Hello,

I checked the transmission fluid today, the level was ok . I noticed that the color of the fluid is red, which means the fluid has not gone bad, right? Also, I might have edit my original question a bit. I noticed carefully the way engine responds to acceleration. The car has hard time picking up beyond 50mph. When press down on the pedal, the engine roars louder, with RPM around 3-3.5K. It roars so much that I feel I am hurting the engine, but if I keep pedal pressed down, it will eventually accelerate beyond 65-70MPH, but takes about 30-45 seconds or maybe more, to get to that speed. So basically the response time is really long. For a car that has 2.4L engine, 135K miles and regular oil change, this struggle to speed up seems odd.
What is the next thing I should look for?
thanks

 

Are the spark plugs and air filter in good shape? Are there any other maintenance items due for replacement changed like an external fuel filter?

A clogged catalytic converter sounds like a possibility. A quick check of the catalytic converter is to hit it with the handle of a screw driver and listen for rattling (broken pieces of the catalyst). Can anyone else suggest other simple tests to verify that the catalytic converter is not clogged?