This car seems to have an issue only during cold but occasionally when extreme changes in weather. It will crank and try to start and seem like it may catch then return to cranking. Compression was tested #1 at 150. #2 at 145. #3 at 150 And #4 at 175. Coolant sensor was changed and double checked resistance at running temp at 350ohms and when cold at -11c at 6k ohms. Seems when it does get running if we try lots it seems like the exhaust is rich and may have flooded. Any thoughts? Runs perfect above 0c or 32f
The compression in 1-3 is a little low, you’d get improved performance if those cylinders were the same as 4. But that’s not likely the cause of the intermittent cranks but doesn’t start. Assuming the routine engine maintenance is up to date (s[ark plugs, air filter, cat all ok), and no diagnostic codes, I’m guessing a problem w/the fuel pressure. If your Sentra uses an engine compartment fuel pressure regulator, one thing you could do yourself is to remove the vacuum hose from it to see if there’s any liquid gasoline in that hose. If there is, you need a new one. Regulator, not the hose. The rich operation could also indicate misfires due to ignition system problems; e.g. intermittent crank position sensor or ignition module.
You might have a leaking injector. When you crank the engine, that cylinder is too rich, but the others lack fuel because the leak has reduced fuel pressure and volume at the injectors.
Try bringing up fuel pressure and volume: turn the key from Off to Run - not all the way to Start - then back to Off. You may hear the fuel pump run for a couple seconds each time. Repeat this a couple or few times, then turn the key all the way to Start. The flooded cylinder may not fire up right away, but the others will, and when it starts and you give it a little gas pedal the flooded one will clear and all will be good. Anyway that’s the hope!