Hyundai Repair: wont start lack of power, fuel pressure regulator, grade fuel

Question
QUESTION: Hello
I have a 2003 elantra and for the past 6 months each morning the motor would fire but would not start once only. After this initial start the engine would start no problems all day. And also appears to lack power.
Plugs have been changed, air filter has been changed and fuel filter has been changed. The problem still persists even also after using premium grade fuel. Any help would be appreciated. I am from Australia but would like your help if possible
Knowles

ANSWER: Hi, Knowles.  I'd like to make sure I understand what's occurring here.  The statement "the motor would fire but would not start" causes a little confusion for me.  Do you mean that the engine starts and then stalls back out, and you can then start the engine normally for the rest of the day?  If not, please clarify whether the starter turns the engine, how long it turns before the engine starts, and whether the engine runs normally immediately after starting.

---------- FOLLOW-UP ----------

QUESTION: Hello
Thankyou for your reply.
Every morning the engine tries to start this initial time engine kicks over, the starters working but the engine fails to keep going (stalls). This is just the initial turn of the key. about 5 seconds I release the key after it fires just doesnot grab and keeep going.
The second time I try the engine runs. After this the engine starts first try all day.
During the day lacks power especially up hill struggles does not have the crisp accelleration (struggling feeling sounds like lack of fuel or timing), hope this helps
regards
Knowles

Answer
A few things come to mind.  The first is possibly a leaky fuel pressure regulator.  This would tend to cause the long crank time, and perhaps even the stall on the initial start, but won't typically cause a lack of power.

Another possibility is that your fuel pump is weak.  This tends to not cause problems so much at initial start, but as the car is driven, typically causes a lack of power on acceleration which will eventually lead to the engine stalling if driven long enough.

A third possibility is that you may have a misfire.  This will typically cause all the symptoms you describe, but will usually also cause the check engine lamp to come on.  

Without being able to feel how the car is running, it's difficult for me to be able to determine the extent to which the lack of power may be related to your stalling.  If you have a local shop that's experienced in working on Hyundais, I'd recommend taking it there.  In this case, it's important for the shop to know how the vechicle normally behaves so they can contrast that with how your vehicle is behaving.