Exhaust noise - bad cat converter or a blow? VIDEO
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Joined: Jun 2017
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Clk230 Avantgarde
Exhaust noise - bad cat converter or a blow? VIDEO
Hi guys,
Have been working through issues on my CLK230 since buying - I have consistently been getting P0101 MAF codes and P0420 Cat below efficiency codes.
I've since replaced the MAF with a brand new VDO Siemens genuine item and now the MPG is back up to 30+ from around 25 - it also changes gears more smoothly and generally feels really nice. The problem is I'm still getting both the above errors (I've cleared the codes before fitting new item)
It surely can't be the MAF again - could a bad catalytic converter cause the above error codes to keep appearing? I've checked the o2 sensor voltages and they seem good..
I've also got this sound coming from the underneath exhaust area, it gets worse when you rev and drive it, is also worse when cold.
I should add that I took it into a cheap exhaust place last week because of the rattle, and they welded this metal bracket back to one of the pipes where it had broken off - they reckon this was causing the rattle - I'm not convinced when considering the cat code P0420 I keep getting..
Have been working through issues on my CLK230 since buying - I have consistently been getting P0101 MAF codes and P0420 Cat below efficiency codes.
I've since replaced the MAF with a brand new VDO Siemens genuine item and now the MPG is back up to 30+ from around 25 - it also changes gears more smoothly and generally feels really nice. The problem is I'm still getting both the above errors (I've cleared the codes before fitting new item)
It surely can't be the MAF again - could a bad catalytic converter cause the above error codes to keep appearing? I've checked the o2 sensor voltages and they seem good..
I've also got this sound coming from the underneath exhaust area, it gets worse when you rev and drive it, is also worse when cold.
I should add that I took it into a cheap exhaust place last week because of the rattle, and they welded this metal bracket back to one of the pipes where it had broken off - they reckon this was causing the rattle - I'm not convinced when considering the cat code P0420 I keep getting..
Last edited by dennis10; Jul 29, 2017 at 02:02 PM.
Thread Starter
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Clk230 Avantgarde
Ok for anyone who is also getting a P0420 code you might find this useful - but basically I have self diagnosed that my catalytic converter is indeed completely screwed.
I'm using a decent app called Torque Pro, that talks to my Bluetooth OBD2 dongle - which has allowed me to firstly identify that the sensors are working within range (voltages should be from around 0.1 upto about 1 volt (usually 0.9) and then secondly monitor both the pre cat and post cat o2 sensors when driving.
The pre cat sensor should fluctuate between these voltages as it measures the o2 level as it comes from the engine, it then feeds back to the ECU telling it whether it's too rich or lean.
Meanwhile the post cat sensor should remain very steady, indicating that the cat has done it's job and the exhaust gases coming out are just the right mix
Both my sensors practically mirror each other, ie both are fluctuating, meaning the cat is not doing its job and the gases are coming out as they went in and not burning off.
This coupled with the above noise and my long term fuel trim being almost -10% meaning it's telling the ECU to put less fuel in as it is too rich means case closed.
The MAF has been replaced with a genuine new one, what else could cause too rich a mixture and also ruin a cat?
I'm using a decent app called Torque Pro, that talks to my Bluetooth OBD2 dongle - which has allowed me to firstly identify that the sensors are working within range (voltages should be from around 0.1 upto about 1 volt (usually 0.9) and then secondly monitor both the pre cat and post cat o2 sensors when driving.
The pre cat sensor should fluctuate between these voltages as it measures the o2 level as it comes from the engine, it then feeds back to the ECU telling it whether it's too rich or lean.
Meanwhile the post cat sensor should remain very steady, indicating that the cat has done it's job and the exhaust gases coming out are just the right mix
Both my sensors practically mirror each other, ie both are fluctuating, meaning the cat is not doing its job and the gases are coming out as they went in and not burning off.
This coupled with the above noise and my long term fuel trim being almost -10% meaning it's telling the ECU to put less fuel in as it is too rich means case closed.
The MAF has been replaced with a genuine new one, what else could cause too rich a mixture and also ruin a cat?
Last edited by dennis10; Aug 1, 2017 at 01:04 PM.
Thread Starter
Newbie
Joined: Jun 2017
Posts: 14
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Clk230 Avantgarde
I know this forum is pretty dead and it's an older car - but can anyone take a look at this noise and give me any pointers to look for? 
I had the cat replaced today (was faulty) and was hoping in the process it would cure this tappy noise - it didn't
Would appreciate some help before I try posting it in the main forum where it might get seen
Thanks
I had the cat replaced today (was faulty) and was hoping in the process it would cure this tappy noise - it didn't
Would appreciate some help before I try posting it in the main forum where it might get seen
Thanks
Member
Joined: Oct 2009
Posts: 141
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From: San Diego CA
'02 CLK 320 2000 clk320
Might be something loose like heat shielding. I
had the rattle awhile back. It was the cats. Someone just replaced your cats and they didn't inspect for other stuff? Get under your car and look. It's free to shake your own cars parts.
had the rattle awhile back. It was the cats. Someone just replaced your cats and they didn't inspect for other stuff? Get under your car and look. It's free to shake your own cars parts.
