I have a 96 maxima that I can't get started. Lately on cold mornings it would start up fine and for a couple of seconds after the engine turned over there would be a loud noise. This would happen everytime the weather would get cold. On warm days it would start up fine. Then a few days ago it wouldn't start at all. It was a cold morning and after talking to a few people it sounded like the coolant sensor. So I changed it out but it still won't start. I did the self diagnostic on the ecm and it came up the knock sensor. My wife puts in the cheap gas so I don't know if that is the reason for the knock sensor code for coming up. Would a bad knock sensor prevent the car from not turning over at all??

Need Mr Daniel the DIY mechanic to tell you...
 

But here goes....
I think if you engine is knocking...it should be knocking when the engine is running....so why would the sensor not let you run when the engine is still off? Unless....the sensor detects or memorize knocks all the time?
ok..not such a great explanation...anyhow....
why wouldn't a car start?
last time I heard that people had problem with cold starting because the temp sensor related with the fuel is messed up (ok..was this a theory or a fact...I dun remember)
In cold weather, air is richer, thus you need more fuel for stoch mix...and vise versa during hot weather...
now maybe that part of your car is messed up.

by the way...how cold is cold? could your fuel filter has frozen..or something along there got frozen...water in the fuel line system <--bad fuel....err....

what about your starter and alternator?
Battery?

I think before wondering about others...check your battery..it should read 12 volts and then you can go and check your alternator at autozone...free...
I dunno how to check starter...
anyhow...hope that helps and not confused you...
good luck

Please be more specific than "it wouldn't start". Did it
- fail to crank (Rrr-Rrr-Rrr), or did it
- fail to fire (Vroom!)?

It fails to fire. It seems like it is not getting any gas.

You could have tested the Engine Coolant Temperature Sensor with an ohmmeter. That test might have saved you the cost of a replacement.

No.

No.

Zprime has a good idea about a frozen fuel filter. Water droplets in the fuel line become tiny ice crytals in freezing temperature. These are solid particles which are trapped by the fuel filter, just the same as sand would be. If there are enough ice crystals the filter becomes clogged. This hypothesis is consistent with your symptoms.

Buy a can of starting fluid. This is a spray can of ether (or equivalent) which you can buy for US$2 at K-mart, Wal*Mart, or any auto parts store. Spray a good ten-second blast of starting fluid into the engine air intake. The starting fluid serves as a temporary substitute for gasoline. If your engine now starts readily, runs for a few seconds, and then "dies", that confirms a fuel problem rather than ignition.

If the starting fluid experiment confirms a fuel problem you might be able to cure it by adding DryGas (or equivalent) to the fuel tank. This will help only on a warm (above freezing) day when the fuel is circulating normally.

The noise could come from a cylinder which fired at the wrong time. I don't see any connection with the Knock Sensor, but this symptom might arise from a bad Crankshaft Position Sensor. If the Engine Control Module (the computer) gets wrong signals from the CPS, ignition timing will be disrupted.

if it fails to start, it could be your fuel pump. i had to get mine replaced 3 weeks ago. it was due to mobil premium gas. the dealer in my area has gotten several maximas with the same problem. the car either didn't startup again at the pumps, or quit shortly thereafter. the fuel fused the seals on the pump. good thing mobil payed for it. see if your dealer can help you out cause its expensive. then again, all maxima repairs are expensive! good luck.