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Discussion Starter · #1 · (Edited)
Hi guys. I have a 2005 300C and I'm to the point where i'm very uncomfortable with driving it. My 300 is very sluggish at times. I have to press a little harder than usual on the accelerator to get her to go and then I have to mash down a little further to get her to get up in speed. It's very annoying and it scares me. Sometimes I feel as if it's going to stop right on the highway. Also, I had my check engine light come on in December. I got it checked out and it came back P0430 Catalyst Efficiency and P0300 Misfire. I figured that the misfire was causing catalytic converter problems so I got the spark plugs changed and codes erased. Light came back on earlier this month, but it only came back with P0430. I know at this point I will need a new catalytic converter.

Do any of you have any recommendations as far as aftermarket cats? Should I get my oxygen sensor checked to see if that may be causing the code? Also, do any of you think that my cat going bad correlates to the car running sluggish and running like it's losing power?

Another thing. The ride is rough! I don't know if it's the shocks/struts/sway bars or anything that assists with the drivetrain and its parts. I don't know what it could be either. I don't have people I can ask and mechanics here aren't helpful in the semi rural area I live in.

Please help out the little baby girl (me) lol. Any and all help is appreciated.
 

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As far as converters you should be able to buy stock and replace the o2 sensors. 340 hp is not something you lose easily. If your having a power loss after that then one tip ill give you is to pull fuse 11 for about a min then replace. After that put the key in and turn to the on position. After all the chimes slowly depress the Pedal to the floor and then slowly back up to the top. Turn the key off and then start. This will help trick the computer and help give some more power... I'm thinking the real loss is the back pressure of the expired converters.
 

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Yes a plugged cat will cause it to feel sluggish, I'm a little scared of aftermarket cats not being able to store enough oxygen on the oxidation phase to reduce HC and CO or being able to reduce NOX gasses if they are single stage and don't have a reduction phase at all. If you had to replace an O2 sensor and only installed one of the four sensors it could potentially cause a cat code, but it's more likely that if your car passed the O2 sensor monitor that it is the cat. For a rough ride I highly suggest that someone check your vehicle over for worn parts, as this can be potentially dangerous. Do you hear any noise, does it pull or drift on the road, any vibrations? You have correct air in the tires and they have normal wear on the tread?
 

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How many miles on the cats?
 

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Discussion Starter · #6 ·
Yes a plugged cat will cause it to feel sluggish, I'm a little scared of aftermarket cats not being able to store enough oxygen on the oxidation phase to reduce HC and CO or being able to reduce NOX gasses if they are single stage and don't have a reduction phase at all. If you had to replace an O2 sensor and only installed one of the four sensors it could potentially cause a cat code, but it's more likely that if your car passed the O2 sensor monitor that it is the cat. For a rough ride I highly suggest that someone check your vehicle over for worn parts, as this can be potentially dangerous. Do you hear any noise, does it pull or drift on the road, any vibrations? You have correct air in the tires and they have normal wear on the tread?
Okk...I'll try to find someone to check it out. I don't hear noise I just feel it; vibrations yes. I've had my tires rotated and balanced because I thought that was the issue. I'm not sure if the air is correct in my tires, so i'll get that checked too. And yes, I have normal wear on my tires
 

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Discussion Starter · #8 ·
Clean the throttle body, change out the EGR valve and change the cats. That should get ya goin' again, baby girl.
I stayed up late last night for a couple of hours researching how to clean a throttle body and I have decided to make it a DIY project for me....i'm excited. Haha..I just hope I don't mess anything up. I want to take off the entire throttle body though so I can make sure it's thoroughly cleaned. You think that's a good idea?
 

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JYHemi, I'm in the same boat as you with regards to my 2005 300C and a rough ride. I thought new shocks and struts would help, but if anything, it's worse now. I feel like I'm driving a truck!
That original, smooth, "floaty" ride I have back in 2005 is now just a fading memory. I know I need to take it in and have the front end maintained. I've read that arm bushings and other parts are probably worn (or gone).
Potholes and bumps make a loud thump sound in my front end, probably caused by worn parts.

But, my 300C still looks pretty good and while I have the new car temptation every once in a while, I still enjoy my 300C and can't imagine another big car payment (yet)!
 

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The OEM bushings were crap on these cars. Worn bushings put a lot of stress on joints and give you a rough ride.

A lot of us have swapped out many of the suspension bushings. There are lots of them.


Removing the throttle body is necessary as most of the grunge will be on the back side. Not hard to do if you follow instuctions posted elsewhere here . . .
 

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In my case, I chose Pedder's polyurethane bushings, as I run the Beast on road courses:

http://www.300cforums.com/forums/su...ifications/82969-bbii-getting-pedderized.html

It was spendy - but well worth it for me. Really improved precision and handling.

Hopefully, others will chime in here with less expensive options.

The OEM's will probably give you another 60,000 or so miles before serious wear sets in with normal driving.
 

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In my case, I chose Pedder's polyurethane bushings, as I run the Beast on road courses:

http://www.300cforums.com/forums/su...ifications/82969-bbii-getting-pedderized.html

It was spendy - but well worth it for me. Really improved precision and handling.

Hopefully, others will chime in here with less expensive options.

The OEM's will probably give you another 60,000 or so miles before serious wer sets in with normal driving.
Read your "Pedderized" write-up. YES, less expensive options would be great! :)
 
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