My 95 Maxima (244000 mi --- great car) is stalling sometimes when it is cold. It is actually flooding which is causing it to stall. After it stalls, the only way to start it is to hold the accelerator down all the way and turn the engine over. When it starts, a lot of black smoke comes out of the exhaust. Once the car warms up, I don’t have any problems. This has been happening for about two weeks now and yesterday the check engine light came on. I took it to Auto Zone and when they read the code it said the knock sensor was bad. My question is --- before I spend $160.00 on a new knock sensor, would a bad knock sensor cause my cold flooding problem or is the flooding causing a false error code on the computer?

 

Try this, it might help. When you get in the car turn the key to the ON position and wait for the BEEPING to stop. Then try to crank it. This way the fuel system is all ready and pressurized.

 

Umm... flooding means that there is already too much fuel in the cylinders... not sure what pressurizing the fuel system is going to do for him... his problem is leaky injector(s). The only reason the knock sensor light came on is because the engine was probably stuttering/running rough because of the overly rich fuel mixture and the ECU tried to compensate (i.e. detected it as knock). However, the knock sensor by itself will not light the CEL - so there should be some other code stored (the knock sensor is a silent code - does not set the ECU).

 

The KS does trigger the ECU but not the CEL. You have to check for it.

 

If you know a fuel injected engine then you know that pressing the gas does nothing when the car is off, its not going to flood the engine. When you put the key in it pressurizes the system for a few seconds. I highly doubt thats the knock sensor. I would suspect a bad cam or crank sensor to be causing that

 

Ant - in the maximas and may other nissans or fuel injected vehicles, holding the accelerator down all the way (WOT) signals to the ECU to clear a flooded condition - it is the correct way to start a maxima with a flooded engine. You are right however, that pumping the gas when the car is off will have no effect on starting the car.

 

Your right, I just wasnt sure if he meant he was doing that or he meant that by him holding it down it was doing the flooding. I still say get the codes checked because most likely like you said the knock sensor code is being thrown because of another sensor. When your 02 sensors are going bad they also tend to trigger the knock sensor code as well. With that high mileage, its kinda hard to tell unless hes recently changed the 02 sensors or cam and crank sensors.

Thats why I miss my old weber carbs... if it flooded just let it sit. If it ran rich, just a screw and it was adjusted. But then again I was burning more gas in the 4 cyl it was in that my Max

 

Yes indeed... I'm at 100k - the only sensors I've ever replaced are the front O2 - and that too, only one posted a code, but I figured that while I was getting dirty - I may as well do both. I'm very tempted to do the crank and cam sensors... but don't know if I want to spend 150 bucks on parts that aren't posting codes - just have occasional hard starts... 1 out of 10.

Agree with you the carb. being so easy to control... all this damn fuel management is amazing - not only have engines gotten more powerful (and continue to do so), but emissions keep going down and mileage goes up or stays the same... The Civic and Corolla are two examples of what technology can do... I used to have an 88 Civic - 28-30 mpg (low for that type of car - it only had 95 hp I think)... now the new civic are much more torquey, same size, if not bigger engines, in the order of 120hp (base I think) and they put out 38-40mpg on the highway comfortably... damn.