HELP: Rough Startups

Tom_O370

I've been having a little issue with my car starting up, If the car sits after being driven overnight or for a few hours it will turn over pretty easily. But if the car sits for 30 minutes to 2 hours after being driven, it takes a few seconds to turn over and when it does its very hesitant in doing so. Also, i want to mention that after being started, then turned off, and started again, it will start right up.

After doing some digging on the forums and research of my own, so far i have replaced the battery, cleaned the battery terminals, put in new spark plugs, cleaned the MAF sensors, cleaned the throttle bodies and did all the throttle relearns but none of those seemed to work. As far as the starter goes, I don't think that'd be the issue because it cranks the engine just fine.

From what I found on the forums and from talking to my mechanic buddy, it seems to come down to fuel delivery being the issue. I don't think it'd be the fuel pump because the car performs just fine. One theory I came up with is that the fuel injectors are leaking and the reason it turns over just fine after sitting for a while is because the fuel has a time to evaporate and therefore is easier for the spark to ignite the leaked fuel. It could also be a fuel pressure issue or even a faulty sensor.

If you guys could help me out and give me some ideas of what the issue might be that would be awesome!


FIXED: REPLACED OEM INJECTORS

ByThaBay

Best thing to do is to datalog the car when the issue is happening and look at the various parameters. This should help you narrow down the issue. I don't think it's a fuel pressure issue, because the fuel pressure will drop to zero overnight by the time you're ready to start the engine and you're not having issues with that.

If you need ecutek data logging hardware or licensing, PM me I can get you set up.

Rusty

Mine will hold pressure overnight. I have a CJM fuel pressure gauge.

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SonicVQ

Is the cranking speed the same in each example?

As for fuel pressure, her is what I have measured from my 2011 G37 last month:
• When the engine is turned off it drops to about 46 PSI from 51 PSI with the engine running.
• After 30 minutes: 45 psi
• After 1 hour: 30 psi
• After 2 hours: 16 psi
• After 3 hours 9 psi
•*After 4 hours 4 psi
• After 5 hours < 1 psi

(This was measured using a Honeywell 100 PSI pressure sensor with CJ Motorsports 2 port fuel tap and my data logger sampling once per second)

There is a TSB (EC07-016A) for the Nissan Versa and it mentions that fuel system pressure needs to be > 29psi after 30 minutes from when the engine is off.

Since that fuel system is very similar to ours (51 psi), I suspect it is a good rule of thumb.