Hesistation/knocking during hard acceleration; failure to maintain 4000 RPM at idle - Mustang Evolution

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Old 01-11-2015, 02:27 PM   #1
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Hesistation/knocking during hard acceleration; failure to maintain 4000 RPM at idle

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!!!
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Old 01-11-2015, 06:14 PM   #2
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Sounds like hat cat(s) are clogged
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Old 01-11-2015, 07:02 PM   #3
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Yeah it might be clogged cats. I had it bad on mine then i just popped on a offroad x pipe and problem solved
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Old 01-11-2015, 09:06 PM   #4
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So, following suggestions and leading up to the last possible culprit, I disconnected my driver exhaust pipe at the exhaust header flange to relieve the back pressure and, although, sounds like a beat up junker, the RPM no longer drops so it is a catalytic converter clogged up. Started doing some research as for the replacement and I'm not sure - apparently there are 2 "catalytic" converters on each side: front and rear - one angled one followed by a straight one. If anyone were to take a guess, which one would get clogged up?

Eastern Catalytic part #s EAST83165 and EAST83425
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Old 01-12-2015, 12:36 PM   #5
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Just get 2 New Hi-Flow Cats & do away with the upper 2 cats. I did this to my 04 V6 Mustang.
No problem what so ever at emissions. I believe I paid $39 ea. at Summit Racing for the cats & another $80 to have them installed. I put an X-Pipe in at the same time & the car sounds Great !!! I believe you also get a slight bit more power with only 2 Cats vs. 4.
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Old 01-13-2015, 02:13 PM   #6
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Theres actually 4 catalytic converters on our cars. Cut them off, sell them to a scrapyard. Get an off road pipe im telling you, you wont regret it!
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