O2 sensors???

Ok my car was giving me problems(it would turn off and had a hard time starting), but i took it to pepboys and they ran diagnostics, said it was vacuum leaks and boom the problem was gone and my car started up quite well.
Every now and then the car threw the check engine light so i took it back to pepboys and they said that their best guess was O2 sensors, everything else checked out fine including starter, but since my car has some performance mods they were not sure...(fuel pressure regulator, hooker headers, exhaust w/o cats)
My car runs great Except it has problems starting again... it turns over...i hear the clah,clah,clah,clah,clah sound but it does that for a while then turns on.
I've noticed it tends to do it more when it is cold out(I live in miami not really that cold:lol:)
Could this have anything to do with the O2 sensors?

Doubtful.
O2's shouldn't give you a hard start.
Fueling could. Fuel filter?

Ok my car was giving me problems(it would turn off and had a hard time starting), but i took it to pepboys and they ran diagnostics, said it was vacuum leaks and boom the problem was gone and my car started up quite well.
Every now and then the car threw the check engine light so i took it back to pepboys and they said that their best guess was O2 sensors, everything else checked out fine including starter, but since my car has some performance mods they were not sure...(fuel pressure regulator, hooker headers, exhaust w/o cats)
My car runs great Except it has problems starting again... it turns over...i hear the clah,clah,clah,clah,clah sound but it does that for a while then turns on.
I've noticed it tends to do it more when it is cold out(I live in miami not really that cold:lol:)
Could this have anything to do with the O2 sensors?

As said by Mr luos
Cold start is not 02 sensors.
They kick in for closed loop pcm operation after warm up.
Year make and engine and mileage would help.
How is tune up end?
Fuel pressure?
What is the code no? Post back code no.
And get a fuel pressure gauge on it at cold start.
See if it is up to specs on fuel pressure.
What was done on fuel pressure mod?
MT

Engine is rebuilt and so is transmission...about 28k miles on it since rebuilt fuel pump is about 6 months old the fuel filter was changed about a month ago.
I dont know how the fuel pressure is all i know is that it has a performance regulator...? I did not put that in there so i dont know much about that.
When i took it in it did not through any codes.
The light comes on and off sparidicly once a week sometimes even less. The mechanic just guessed it was O2 sensors.
How can i check the fuel pressure... does autozone or advanced autoparts do it for free????

Rebuilt fuel pump??

missed a comma after rebuilt:banghead:...fuel pump was new

...guys???

Every day that goes back my car takes longer and longer to start... How can i chack the fuel pressure...can i do it myself...help

Stealership.

Sucks...but that is all I have got for you.
I have a gauge at my fuel rail for pressure.


Might as well have your charging system checked again.

?...Stealership
Charging system...you mean battery and alternator...

Stealership = Dealership

Correct about the charging system. Sounds like maybe your battery doesn't hold a complete charge.

Hey Lous...
Besides that can spark plugs have anything to do with it, mine have not been changed in a while...
What is the "opti-spark" could that cause this too...
Thanx alot man this shit is drving me crazy...

Is there any chance the coolant temp/air temp sensors are causing this problem? If the computer thinks its like -40 degrees outside it will dump fuel and vise versa. I doubt this is it, but I can't think of anything else off hand right now.

Plugs could if for some reason it is a weak spark. But most likely it wouldn't run as well as before.