Just recently (past two weeks) the car has begun to backfire on the top-end it was around 4500 and up but yesterday I replaced the stock coil with and MSD blaster and after testing some more the car is now pulling up to about 5500 without a problem I know that the stock Opti's tend to lose spark energy on the top, the car has had the plugs and wires changed just 3000 miles ago and the couple of plugs I pulled looked okay. The cap and rotor was replaced about 3 years ago according to receipts from the former owner by a local shop. The car has been running fine otherwise, I work at an O'reilly auto parts so I checked the ignition module and it checked out. Any ideas, I can get a scan tool to check it out but haven't yet. The only mods are listed in my sig.

 

Check your fuel system....while getting on it.

 

mayb u need a new fuel filter? thats wat happened to me, i changed it and everything went back to normal.

 

I replaced the fuel pump just a few months ago, but I just used a factory Delphi pump I didn't think I needed anything more considering I just drive the car daily and my level of modifications. While I did that I also replaced the fuel filter. Was my choice of a stock pump wrong? I am going to try to get a fuel pressure gauge, but everything I have found is either mechanical that goes under the hood, which isn't going to help me when accelerating down the streed or they're like $230+ for and electric gauge and sender. If anyone knows of a mechanical gauge to put in the vehicle that would be helpful or any other way?

 

What kind of fuel pressure should I see sitting idle?
and what should I see at wot?

 

i had mine tested and the mechanic said it the fuel pump was perfect at 41 idle, 47 WOT.

i tested mine because i had the SAME EXACT problem as you. replaced damn near everything but the opti and i still have the problem