2005 Mercedes S500 Misfire Problem
01-19-2019, 03:43 PM
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2005 Mercedes S500
2005 Mercedes S500 Misfire Problem
Hello all! This is my first post, ive been lurking around here for a couple of years and found many useful things but never joined, i have a problem with my car and was hoping to get some feedback from you guys. So my car has been misfiring for the past 2 months, i havent been driving it and been using a beater car, the car is a 2005 Mercedes S500 with 113,xxx miles on it, its been to 4 shops and 1 Dealership already and no one can figure out what is wrong with it. Ive changed the Spark Plugs, Spark Plug Wires, ignition coils, Fuel Filter, Intake Manifold Gasket, Throttle Body Gasket, All of the PCV Hoses, All of the Fuel Injectors, Valve Cover Gasket (it was leaking oil, i thought maybe oil was getting into the spark plug holes) And none of that helped. Ive also had the ECU sent out and tested, and the ECU is completely fine. Im getting alot of codes, a P0300 Mutiple random misfire
P0305 Cylinder 5 Misfire
P0306 Cylinder 6 Misfire
P0307 Cylinder 7 Misfire
P0308 Cylinder 8 Misfire
And recently i got a P0102 Mass or Volume Air Flow A circiut low
ive cleaned the mass air flow sensor and it still shows the same code, i ordered a new MAF and itll be here tomorrow, going to swap that out and change it.
So when i start the engine, it idles steadily its not jumping up and down, but it sounds wrong, and it has a bad smell, a strong fuel smell to it. When im driving and i hit the gas and get it up to 3.5-4k rpm, the Check Engine light starts flashing and it misfires on the whole entire driver side engine bank, 4 cylinders misfiring. Yesterday as i was pulling into my driveway, the engine died on me completely (first time, never died on me before) One of my mechanic friends says he had a very similar thing, and it ended up being a bad O2 sensor, he changed the O2 sensor and the car ran good again.
What are your guys thoughts?
Thank You
P0305 Cylinder 5 Misfire
P0306 Cylinder 6 Misfire
P0307 Cylinder 7 Misfire
P0308 Cylinder 8 Misfire
And recently i got a P0102 Mass or Volume Air Flow A circiut low
ive cleaned the mass air flow sensor and it still shows the same code, i ordered a new MAF and itll be here tomorrow, going to swap that out and change it.
So when i start the engine, it idles steadily its not jumping up and down, but it sounds wrong, and it has a bad smell, a strong fuel smell to it. When im driving and i hit the gas and get it up to 3.5-4k rpm, the Check Engine light starts flashing and it misfires on the whole entire driver side engine bank, 4 cylinders misfiring. Yesterday as i was pulling into my driveway, the engine died on me completely (first time, never died on me before) One of my mechanic friends says he had a very similar thing, and it ended up being a bad O2 sensor, he changed the O2 sensor and the car ran good again.
What are your guys thoughts?
Thank You
01-20-2019, 02:51 PM
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If it's not an O2 sensor, then it could be a clogged catalytic converter. The inside of the front converter will sometimes break apart and clog the second converter creating too much back pressure on one entire bank of cylinders and causes misfires.
If this is the cause......you could loosen (or remove) the lower O2 sensor (creating an exhaust leak) enough to relieve some of the pressure from building in front of the rear converter. You'll find you won't get the misfires until you really get on the accelerator hard. The bigger the exhaust leak you create, the harder you can drive before the misfires start.
I've had this same problem back in August of 2017 driving from Massachusetts to Wyoming and back. I ended up drilling holes in the front of my rear converter to relieve the pressure. It worked until I hit the mountains of Pennsylvania and I started to get the misfires again.....too much load = too much back pressure.
This is all just a possibility.....but I hope for you, it is as simple as swapping out an O2 sensor.
Good luck.
If this is the cause......you could loosen (or remove) the lower O2 sensor (creating an exhaust leak) enough to relieve some of the pressure from building in front of the rear converter. You'll find you won't get the misfires until you really get on the accelerator hard. The bigger the exhaust leak you create, the harder you can drive before the misfires start.
I've had this same problem back in August of 2017 driving from Massachusetts to Wyoming and back. I ended up drilling holes in the front of my rear converter to relieve the pressure. It worked until I hit the mountains of Pennsylvania and I started to get the misfires again.....too much load = too much back pressure.
This is all just a possibility.....but I hope for you, it is as simple as swapping out an O2 sensor.
Good luck.
01-20-2019, 03:48 PM
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Thank you for the replies! I will be getting an O2 sensor this week and hopefully it will fix it. Thats an intresting fact that the ECU shuts down that bank to protect the cat. I will post back once I swap the sensor with the results.
01-21-2019, 11:35 AM
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2009 E350 4M Avantgarde;mistress 2002 S600; wife 2014 C300 4M
If it is a hopefully partially blocked cat, one way is to stick a small camera into it to verify.
The trick is to get the cat to "fire up" again, and to thus clean out.
If the new O2 sensor doesn't do it, there are "cheater" O2 sensors on the net (or mini cats that attach to them; not expensive).
On my 2002 worked like a charm; never had a problem since.
The trick is to get the cat to "fire up" again, and to thus clean out.
If the new O2 sensor doesn't do it, there are "cheater" O2 sensors on the net (or mini cats that attach to them; not expensive).
On my 2002 worked like a charm; never had a problem since.
01-21-2019, 10:08 PM
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Update: changed the O2 sensor tonight. Didn’t help same exact problem. I took the O2 sensor out and took it for a test drive and I got a lot more power and it burned up a little cloth where the hole for the O2 sensor is so I’m guessing that my cats are clogged I’m going to be taking them to get them gutted on Saturday and hopefully that will fix my problem.
01-26-2019, 04:59 PM
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So I gutted my cats with a buddy today, and its all good! Everything works as it should now! Thanks for the help! Now im completely straight piped😂 No Mufflers, Resonators, and 4 cats gutted, sounds mean! After changing all those things and im assuming it had a partially clogged cat ever since i bought it, this thing really hauls now!
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01-27-2019, 12:49 PM
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I am sure the straight pipe move on these sounds pretty bad ***. Glad you figured it out. Upside is you pretty much built yourself a solid car trying to diagnose this. These forums are the best.
01-28-2019, 10:01 AM
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It sounds pretty mean! Not for everyone though, its pretty loud, personally I love it, but I know alot of people would count this as way to loud 😂 Yeah this thing is ready to go for a very long time with all the stuff that i have done.
01-28-2019, 07:57 PM
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That's great that you were able to fix the situation and have a car you like now. Loud isn't for everyone....but it is for some. 
Enjoy!!!
Enjoy!!!
02-14-2020, 12:54 PM
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I have the same problem
So I gutted my cats with a buddy today, and its all good! Everything works as it should now! Thanks for the help! Now im completely straight piped😂 No Mufflers, Resonators, and 4 cats gutted, sounds mean! After changing all those things and im assuming it had a partially clogged cat ever since i bought it, this thing really hauls now!
02-14-2020, 01:13 PM
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Thank you so much will try that but with min is only cilinder 2 i never had problems with any other cilinders and somtime missfire sometimes not is weird and when a read the code sometimes is system to lean sometimes cilinder 2 missfire I changed the spark plugs the wires coil all that stuff vacuum pipes but still the same . Will try this i hope will fix my problem cos I really like that car has only 80k miles
02-14-2020, 01:27 PM
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