1994 Nissan Sentra - Inconsistent Starting Problem

I hae a 1994 Nissan Sentra that has an inconsistent starting problem. The car either cranks and starts immediately or will crank over only.
When there is a problem, I can get it started by cranking the engine over for a very long time provided the battery doesn't go dead or sometimes it will start if left alone for several days or weeks. When I can get it started after a problem, it starts up right away when turned off and started again.
There is fuel at the engine so it doesn't appear to be a fuel pump problem. There is also spark at the distributor from the coil so that part seems okay as well. Putting starting fluid spray in the air filter doesn't help.
The problem seems more likely to happen at the beginning of a day when it's been cold out (under 50 F).
The spark plugs and wires were changed in the past and the car runs okay if it starts -- it's just a slow car without much power.
The service engine light is on sometimes. The car can have the starting problem no matter if the service engine light is on or not. I don't know how to get a code other than take the vehicle to a dealer.
My guess is there's a sensor issue, but if so, which sensor? Has anyone had an issue like this and what would the recommendation be?
Thank you.
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always_studying wrote:

If you live in an environment with salt-laden air, and the starting problem only occurs when the humidity is high, then wipe clean all high tension insulators (plugs, leads, distributor cap, rotor).
John
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go to any "advanced auto parts " or "napa" or similar chains and the will read the code for free . dick
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I suspect they will not, a 1994 Sentra is pre-ODBII (so is a '94 anything)

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Live between Lake Michigan and Missippi river so there's no salt-laden air. Thank you for the suggestions.
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If you have an old Fuel filter, it can cause intermittent flow of fuel. Check your spark plug's gap, make sure they are even because your "Engine Service"'s light is telling me that something was wrong with your combustion previously, either you put the dirty fuel in or you made it produce too much toxic gas with uneven gapping. This problem could spread to damaging distributor's contact(s). Not saying they already happened, maybe....

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This one seems like a serious problem. In reading the other posts a couple of comments come to mind: Your location may not have salty air but what about salty roads? Where do you spray the starting fluid? If you spray any liquid at the air filter, the air liquid will stay there. Or do you mean you spray it in the housing, right by the MAF? You mentioned that the spark plugs and wires were changed in the past, how long ago? what about the distributor cap and rotor?
For a cranking car to start you need three things: Air/Fuel mixture, a source of ignition and an engine in acceptable mechanical conditions. Even though your tests seem to indicate you have them all, by the car not starting, it is obvioius you do not. For a your car, the only sensor that may prevent it from starting is the camshaft position sensor inside the distributor.
To read the codes, you need a small flat screw driver, the ignition key and the procedure that can be found on the service manuals that can be found online for free.
I have a few questions:
Is yours a SR or a GA engine?
When the car does not start, after cranking, does the exhaust pipe smell to unburnt fuel?
When the car finally comes on, does the engine run normally or it stumbles and misses?
The procedure I would follow to diagnose this problem is:
Is there fuel pressure in the hoses leading to the fuel rail? (does the hose get hard when you turn the ignition key on?)
Can you start the engine when you depress and hold the gas pedal to the floor, cranking the engine for 10 seconds at a time?
Mark the position rotational position of the distributor with respect to the engine head so it can be put back together in the exact position it was, remove the distributor but keep it connected. With the ignition key on, can you hear the fuel injectors click when rotating the distributor shaft?
If you remove a high tension wire from a sparkplug, and with the use of insulated pliers hold the tip of the wire (not the insulating boot, may need to use a metal rod or similar object) at 1/4" from the tip of the spark plug electrode, and crank the engine, can you see the spark jump?
Are the spark plugs fouled?
I hope this info helps.
Good luck!
always_studying wrote:

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