Thought I would post this to you since you appear to know a a lot about the MAX, but anyone else's opinion would help. I have been having what can best be described as a loss in dependible or constant power. Sometimes the engine does not pull as hard as I think it should. It feels like the cars not getting enough juice and full power to the engine is not being produced. I replaced the fuel filter about 7,000 miles ago and even took off my throttle body and cleaned it with TB cleaner with a new gasket in there obviously. This did not help. I have 61,000 miles on the car and always put in at least mid grade gas. All I can say is that the car sometimes pulls hard and sometimes it does not, and no I don't believe that I have become numb to the normal pull of the car through daily driving. I have not had my 60 tune-up done and refuse to pay the dealer to do it( I'm pretty mechanically inclined). Is there something that needs adjusting, a sensor not always working, or has the VQ failed me. Thanks in advance for the help.

 

The 60K mile scheduled maintenance includes new spark plugs and air filter. The 60K work may be done by anyone... the dealer, an independent service provider, or the owner himself. You can save money by doing it yourself. See http://integra.vtec.net/geeser/megamax/60k_service.html for guidance but be aware that page goes beyond Nissan's 60K requirements.

If the sluggish feeling is not eliminated by the 60K service then you should consider testing your front Oxygen Sensors and making a fuel pressure test. The fact that your fuel filter is only 7K miles old is insignificant. It takes only one tankful of contaminated gas to clog a filter. Therefore the service life of a filter could be ten days or ten years, there is just no telling.

 

This obviously happens when the car is hot right? My cousin asked me the same question and I think it may have to do with the tranny. If you have an auto tranny, it seems like it doensn't want to downshift. This is why I am going to go for a ValveBody upgrade, quicker shifts.

 

No, I'm manual, but thanks for the advice. I replaced the plugs about 20,000 miles ago, but will not hesitate to do it again, Daniel do you think new wires would help in conjuction with plugs? Also, how is the O2 sensor tested, and fuel pressure as far as that goes. What effect does a bad O2 sensor have on the car, and how much to replace? I hate to say it but I often get the gas down to the warning light level, I'm sure this is not good for the filter right? So many questions + Daniel = so many answers. Thanks.

 

Our VQ30DE engine does not have spark plug wires.

 

True, I fo got. Now what?

 

There are electronic testers made for this specific purpose. In addition, a technician with an automotive oscilloscope can test Oxygen Sensors. The signal from a healthy sensor varies from a low threshold (around 0.2 volts) to a high threshold (around 0.8 volts), and it sweeps back and forth between those extremes about 10 times per second. If the scope trace shows the Oxygen Sensor signal failing to reach either extreme, or oscillating between them at a frequency slower than 10 cycles per second, that is evidence of a "tired" sensor.

For more information about Oxygen Sensors see: http://www.volksparts.com/o2sensors.htm
http://members.aol.com/carleyware/library/o2sensor.htm

 

Bleed the fuel rail pressure by pulling the fuel pump fuse and making several attempts to start the engine (it won't start). Install a T-fitting with a pressure gauge in the flexible rubber fuel line just downstream of the fuel filter. Install the fuel pump fuse. Start the engine. You should see the pressure maintain a stable 34 psi. After turning the engine off the fuel system should hold pressure for a long time, 24 hours or longer. If the residual pressure bleeds off in only one or two hours that is a sign of a problem... bad fuel pump check valve, injectors with an internal leak, bad fuel pressure regulator, or an external fuel leak.

This is a standard diagnostic test. You will find instructions and a diagram or picture in Chilton (page 5-3) and Haynes (page 4-3,4).

 

The symptoms are increased fuel consumption, decreased engine power, and a feeling of sluggishness. The throttle response is not crisp, like it was when the car was new.

 

A good quality Oxygen Sensor costs about $80. Installation is something the home mechanic can do.

 

It probably does no harm. However, it is bad to actually run out of gas. The fuel pump is cooled and lubricated by the liquid around it. If the tank runs dry the fuel pump may be harmed. The damage doesn't always show up right away.

 

Daniel, maybe my car eats too much gas 11 miles per gallon in city driving could be caused by bad oxygen sensor? because my mechanic cannot find anything rong with my car except one thing that it eats too much gas while comparing to other maxima cars of my friends who get 15-16 miles per gallon in city driving. My car is GLE 1997 has 40k miles on odometer, but i doubt it, and feel it was rolled by delaer before it was sold to me. Would i be able to install oxygen sensors on my own and how many our maxima has? price of all of them?

Thanks!

 

The stop-and-go urban driving environment is the worst case for fuel economy. Perhaps your car gets worse mileage than your friends' cars because ...
- "tired" Oxygen Sensors
- obstructed air filter
- sticking fuel injectors
- defective fuel pressure regulator
- obstructed fuel return line
- bad Engine Coolant Temperature Sensor
- obstructed Catalytic Converter
- fuel leaks
- dragging brakes
- your friends lie about their gas mileage

I hesitate to answer questions like "would I be able to install ..." because I don't know you. I don't know if you have lots of automotive service experience or you just figured out where the engine oil dipstick is located. I don't know if you have $5K worth of tools or your tool kit consists of a claw hammer and toilet plunger. I suggest you read up on this procedure in Chilton or Haynes and decide for yourself if you can handle it.

Our 4Gen Maxima has three Oxygen Sensors. The two front sensors are located in the Y-pipe and the Engine Control Module uses signals from them to manage the fuel mixture. The rear sensor is located just downstream of the Three-Way Catalytic Converter. Under normal conditions the rear sensor is used only to monitor the condition of the Cat. Therefore you would be interested in replacing the two front sensors. They cost about $80 each.