Hi all, new to the board and hoping for some help diagnosing an issue with my 06 GT.

A few months ago there was a day I drove the car pretty hard. The next day when I was out driving like normal, I had a random misfire and since that moment the car has been running rough - at idle and cruising around town it's mostly OK, but give it any real acceleration and you can feel the engine sputter/flutter/bog down and there is a severe lack of power.

Haven't driven it a ton since then, but still occasionally (just no hard acceleration) and the CEL never came on again for a misfire, but the fluttering and power loss was still clearly there. I cleaned the MAF and that didn't do anything.

Finally had the time to try and work on it, and replaced the fuel filter. The car seemed to be running like normal for about 5 minutes, then I accelerated up the on ramp to the parkway and I popped a cylinder 8 misfire.

From there I replaced the coil above cylinder 8, checked and cleaned all coils, plugs, and fuel injectors. Misfire fixed, but original fluttering and loss of power returned, so replacing the fuel filter did not work.

Summary:
Car idles and drives at low stress OK, but sputters/flutters/bogs down with a severe lack of power on any meaningful acceleration. CEL has only come on twice for cylinder misfires.
The following has already been done and hasn't fixed the issue:

• Cleaned MAF sensor
• Replaced fuel filter
• Checked all plugs, coils, and injectors

Car has a little under 80k miles on it. Has a Whipple supercharger with intercooler and a cold air intake. Everything else including the throttle body is stock (so far as I know - I bought it modded).

Any ideas on what to look at next? The only other possibilities in my head are fuel pump or a bad cat.

Thanks!

 

Scan the ECU for fault codes and if you have an SCT tuner, plug it into your OBD II port and do some datalogging. If you have a fuel pressure gauge, see if it drops when the engine splutters.