I've got a 2003 LS....CAI, downpipe, cat, Borla cat-back. I changed the fuel filter and plugs/wires a few months ago. The clearance with the new exhaust and downpipe is about an inch shorter than stock, making the rear plugs extremely hard to get to by myself, so I only replaced the front plugs and wires until I can get an extra set of hands to help out. Almost immediately (within a week) the car started to hesitate at 2/3 to full throttle and got progressively worse until its a noticable drag on power. This only happens when it's floored and doesn't affect driveablility other than when passing. There are no codes set. Any ideas?

 

did u recheck the plugs to make sure they were in correctly and tight?

 

I haven't yet, but I will. I figured that if it were an ignition problem, it would run rough throughout the throttle range instead of just WOT. I'm still leaning towards fuel starvation or clogged injectors. If it were MAF or IAT, I would get engine codes. The same thing with a misfire (unless possibly half of the plugs are pulling harder than the other half and it's confusing the computer). My next guess would be the fuel filter I installed being faulty. I really need to check the fuel pressure and see what happens. It may be getting enough fuel unless I have a load on it. Then there's the possiblility of a bad TPS. Just thought I'd throw a few suggestions out there and see if anyone had the same problem or maybe some other theories.

 

yeah, recheck the plugs. the fuel filter was what iwas thinking before i even read your post. if its not that, it would probably be the fuel pump. otherwise, it would be some electrical issue.

 

Got it...plug wires. I decided to punish it a little and finally got a flashing MIL. I knew that one without having to look it up, so I pulled over and checked wires. The number 3 and 5 had gotten up against part of the exhaust and the insulation had slid back a little. The old wires had finally arced through and were starting to ground out.

 

I'm glad that you figured it out. Good learning experience though.