04 Sentra Long Cranking At Warm Starts

[Fitz98]

Looking for some ideas about what to consider might be the problem.
2004 Nissan Sentra 216k miles.
Car starts perfectly on cold starts. Car would sometimes sit for months and crank right up. Same thing when just sitting overnight.
After it warms up, like a short trip to the store, it would take several seconds of cranking to get it to start. Sometimes it starts with keeping the engine cranking, sometimes it might start just a little better to crank it a little, then re-crank it. Then it will usually studder for a second or 2 and then run fine again.
No CEL.

 

[Bud_One]

ECU engine coolant temp sensor would be my first check.
Not to be confused with the instrument cluster engine coolant temp sensor.

If it's reading colder than the engine is, it may be dumping more fuel than needed when starting a warm/hot engine.

 

[atikovi]

You need to 1) scan for codes and 2) connect a fuel pressure gauge to see what's happening.

 

[Fitz98]

I should add that this is not a new problem. It has been this way as long as I have had the car for about 18 years. Don't know if it did this since new or not. One mechanic said this was normal for these vehicles.

 

[xmanjeff]

i had a toyota truck that did that , check valve bad on fuel line , fuel draining back to tank ,
turn key to run position to fire fuel pump for about 30 seconds then try starting and see what happens

 

[JB250]

I had a 2005 Sentra. It was a cam sensor that caused the hard starting. It was easy to change and did not cost much.

 

[Nessism1]

Tight valves can cause hot start problems.

 

[Fitz98]

Just hooked up my scan tool.
No DTC's.
I don't have a fuel pressure reading on my scan tool and don't have a fuel pressure gauge. I can look into this.
Regarding cam sensor...could be. I replaced the crank sensor a long time ago, but that was when the car would die completely. I did not change the cam position sensor though. Could be a failing crank sensor as well maybe?
Wouldn't a bad sensor throw a code?
I was able to change my coolant temp sensor values on my scan tool, and there was noticeable changes as I changed the temperature values, so I assume that is working correctly. I forget the actual value, I think it was around 177 at idle for a while. How could I better check the temperature? Do I need to put a thermometer into the coolant tank and cross check that actual temperature with the scantool?
30 second key on engine off did not change long start condition.

 

[Nessism1]

Interesting that you mention fuel pressure. Those cars were know for fuel pumps with sticking check valves. My old Sentra had that problem. Changing the pump is easy enough, just be sure to get a new large O-ring.

 

[D60]

Just hooked up my scan tool.
No DTC's.
I don't have a fuel pressure reading on my scan tool and don't have a fuel pressure gauge. I can look into this.
Regarding cam sensor...could be. I replaced the crank sensor a long time ago, but that was when the car would die completely. I did not change the cam position sensor though. Could be a failing crank sensor as well maybe?
Wouldn't a bad sensor throw a code?
I was able to change my coolant temp sensor values on my scan tool, and there was noticeable changes as I changed the temperature values, so I assume that is working correctly. I forget the actual value, I think it was around 177 at idle for a while. How could I better check the temperature? Do I need to put a thermometer into the coolant tank and cross check that actual temperature with the scantool?
30 second key on engine off did not change long start condition.

The ECU should be seeing "real" coolant temp and not the gauge sender, assuming there are two. So, your scan tool is seeing what the ECU sees.

After running awhile if you're anywhere near thermostat temp I think your sender is fine. The point was that if you know the engine is up to temp but the ECU is seeing, say, 50F fuel mixture may be way off.

I don't know at what delta it significantly affects mixture, though, and I'd suspect it's relative, ie the difference between 30 and 50F seems more important than 170 vs 190. Maybe not.

 

[D60]

Oh also don't try 30 second on -- the pump only primes for the first ~3 seconds. Try key on/off at least three times, preferably making sure you hear the pump hum each time, and don't turn it off (then back on) until the pump stops humming.

If this makes it fire off every time, you're losing fuel pressure when not running and when something is hot. I think this is unlikely to be the case, but it's easy to check.

Also, some Nissans and others don't prime every single time. I'm not sure if it's time-based or looking at fuel rail pressure, but I had a '14 Rogue that wouldn't prime with EVERY turn of the key if you kept doing it. Pretty sure an SJ Forester, also. 2004 may be crude enough it's not this "smart," though

 

[72C10]

I will 2nd checking the fuel pressure. Check it while it's priming, running and how quickly it bleeds off after you cut the engine off.