3.8v 2001 Mustang
with GT exhaust conversion.
Gradually my car started hesitating during acceleration. At first I felt it on the highway when accelerating around 60-70MPH, within few days it got worst and eventually it started happening at 30MPH. Now acceleration is very slow, pushing gas to the floor results in metal pinging noises.
If I'm not driving, it idles fine, engine doesn't vibrate much. Now, I noticed if I raise the RPM to around 3500-4000 and hold the gas pedal (while on neutral, not driving), without moving the gas pedal, my RPM starts to drop and the engine sounds really weird. When the RPM drops to 2000, if I release the gas pedal, my RPM drops to around 300-400 and the car almost stalls, however it doesn't and slowly recovers to 800 RPM for yet again smooth idle.
I already spent over a month (on weekends) tested ignition pack, replaced plugs, wires. Had a weird noise in the fuel pump and replaced it as well, although the fuel pressure is around 40PSI. I also checked cylinder compression, fuel pressure and replaced my upper manifold gasket. All good. In the beginning I had misfire codes on 3 cylinders (4/5/6 driver bank and random misfire code: p0300,306,305,304) and lean code p0171. After all the replacements, I no longer get the codes but the car is still doing the same thing.
There's a very strong, almost eye burning smell of exhaust on the driver side of the engine. My friend mechanic suspects I have a clogged catalytic converter. This is a v6 with GT exhaust (h pipe) so I have two ports of exhaust exit.
Is he right and I should replace the catalytic converter? Any other suspects? This problem has been driving me up the wall.
Thanks guys and gals!!!