NISMOPower

iTrader: (2)

I know you had this topic before but i just need to get things clear. Ok I have a 97 GLE Stock w/ 68000miles. My car stalls a lot while i'm either waiting for a stop light or if i'm just cruising between 1k-2k rpms. While i drive between 1k-2k rpm I can feel like the car doesn't get enough gas and you feel a little jerk. So about 2 months my car only stalled while i was driving. So we take it to a car shop. Now the guy said he worked in the nissan dealership before and said that I need to replace an O2 sensor. I came to the forum and everyone said that if the O2 sensor was bad then the Check Engine Lights would appear which it didn't and still hasn't. So i didn't get it replaced. I put a new tank of gas in and the car worked fine. Now I started with this problem again. I tried the Cheveron Fuel System cleaner and that doesn't seem to work. Now the last post i saw you said it was most likely was the fuel injector. So what do you think and how much will it cost if i needed and O2 sensor or fuel injector replaced????
Thanks and sorry it's so long.

Daniel B. Martin

This is not true.

There are two degrees of failure.

1) The Oxygen Sensor is "dead".
The signal from the Oxygen Sensor is outside the normal range, or completely absent. The Engine Control Module (the computer) turns on the Malfunction Indicator Light and stores one or more Diagnostic Trouble Codes. This failure mode is obvious because of the dashboard warning light.

A dead Oxygen Sensor is a severe failure and should be repaired promptly.

2) The Oxygen Sensor is "tired".
The Oxygen Sensor still works but it responds slowly to changes in the oxygen concentration in the exhaust stream. There is no MIL or DTC. This failure mode is less obvious. 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 "tired" Oxygen Sensor is still doing its job, but not performing well.

A tired Oxygen Sensor is not a severe failure and the car may be operated safely.


You may have your Oxygen Sensor(s) tested. 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

Daniel B. Martin

I don't associate these symptoms with a bad Oxygen Sensor.

Most 4Gen Maximas have three Oxygen Sensors. There are two "front" Oxygen Sensors, one mounted in each branch of the Y-pipe. There is one "rear" sensor mounted just downstream of the Catalytic Converter. The Engine Control Module (the computer) uses the signals from the two front sensors to control the fuel mixture. When the front sensors are operating normally the rear sensor is used only to monitor the performance of the Catalytic Converter.

It seems improbably that both front Oxygen Sensors are bad, but neither failure turned on the Malfunction Indicator Light, and that the trouble symptom is stalling. I think your technician isn't trying hard enough.

Stalling when the engine is idling may be caused by a variety of problems including ...
- vacuum leak
- stuck-open Positive Crankcase Ventilation valve
- stuck-open Exhaust Gas Recirculation valve
- faulty Idle Air Control Valve - Auxiliary Air Control valve

Stalling with the vehicle in motion may be caused by a variety of problems including ...
- bad fuel pump wiring connections
- bad fuel pump relay
- bad ignition switch
- bad Throttle Position Sensor
- bad Engine Control Module relay
- low voltage in the electrical system

I wish I could pinpoint your Maxima's problem, but that isn't possible. Someone has to do some serious diagnostic work on this engine. It's quite possible that your engine has two problems and the combination of symptoms makes a confusing picture.

dwapenyi

iTrader: (3)

I'm not DBM, but I'd like to make a suggestion:

When's the last time you replaced your fuel filter?? I would suggest you try that simple step 1st. Maybe it's completely clogged from never having been changed since the car was new.

DW

NeverEnough

I had similar problems when I first bought my Max, and it turned out to be my MAF sensor malfunctioning, which, in turn, caused my fuel pump to work too hard, causing it to eventually die. I am not saying that this is your problem, and I hope it isn't because these parts are NOT cheap, but I do think it would be worth it to check everything before you go replacing things. It just makes sense to look before you leap. My main reasonn for thinking that it may not be your fuel injector is my mileage and my lack of fuel injector issues. I currently have 182,000 miles, and no problems whatsoever with my injectors (I ohmed them). I know that all cars are different, and your problem may be completely different than mine, but I have not seen many people, in my limited time here, that have had major issues with fuel injectors. BTW, do you use premium gasoline in every tank? It's a good preventative measure as well as being best for our engine's timing, compression, etc. I've already rambled on, so, I will go now, but I hope this helps you in your quest to track down this gremlin.

Lee DeVine

Daniel B. Martin

The fuel pump runs continuously as long as the engine is running. It is always working hard, in the sense that it is always pumping against the 34-43 psi pressure which is maintained in the fuel rail by the fuel pressure regulator. Please explain how a Mass Air Flow Sensor can cause a fuel pump to work "too hard". I'm always eager to learn more.

NeverEnough

I did not mean to imply that the MAF increased the necessary pressure, thus overworking it. My intention was to illustrate that the cause of my stalling was due to flooding, caused by the faulty reading, and that the symptoms did not lead me directly to the MAF, but to the fuel pump first. It was only after I replaced it, after determining that it was only running at 11-12 psi, that I looked further to find out that the rich condition my car was running at was not caused by a bad FPR or stuck injector, but was caused by a faulty reading by the MAF sensor. I was half asleep when I wrote the post, and did not read over it enough to realize that I blamed my problem with my pump on the MAF, which is a little embarassing. My thanks for questioning it, you were right to do so.

The point: symptoms are not always indicative of a sigular problem in cars like ours, as the systems are intertwined and one problem can, and more often than not, does lead to a host of other problems. So, look at every possible culprit, and even when you do find one fault, do not assume that it is the cause of the problem, as it may well be yet another symptom of a greater problem somewhere else.

Thanks again, and sorry for the confusion.

Lee DeVine

Daniel B. Martin

You are quite right, and this is an important lesson for us driveway mechanics. One good example is Oxygen Sensors. Consider this scenario...

The dreaded Malfunction Indicator Light goes on and the Diagnostic Trouble Code points to a bad Oxygen sensor. The sensor is replaced and the Engine Control Module reset to erase the stored Codes. Three weeks later the MIL is back, and with the same Code. How could this happen?!? The answer could be that one or more fuel injectors is sticking open, causing those cylinders to run rich. The resultant incomplete combustion produces black soot which coats the sensing element of the Oxygen Sensor with a crust of deposits. The original sensor failed, but not because of age or quality. The replacement sensor failed prematurely because the root cause had not been recognized and corrected. Both sensors were innocent victims in this drama.

There is a great temptation to put too much trust in the diagnostic capability of the ECM. In this scenario it told the truth, but not the whole truth. The good technician would replace the Oxygen Sensor. The excellent technician would do that too, but he would also look for underlying problems and fix them as well.

NISMOPower

iTrader: (2)

So what are you saying I should check first? Cause when I went to she shop before. They said that the O2 sensor was bad and the fuel mixture was too lean or something.....

emax02

iTrader: (1)

Definatly check your MAF sensor first, I think that is your problem.

NISMOPower

iTrader: (2)

Ohh yeah....and sometimes my car won't start. Well it starts up then really fast, it shuts off again. I have to press on the gas pedal to get it kinda starting to keep it running then i have to shift it into drive then go. Is that really bad to do that around 1-2k rpm?

Daniel B. Martin

That depends on engine temperature. It is not harmful if the engine is already warm. It is not advisable to race a cold engine. Keep the rpms as low as you can, and still keep the engine running.

Several people made posts in this thread suggesting specific diagnostic tests. Which tests have you made? What were your findings?