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P0300, p034, p0305, p0306. NEw cats, plugs, air filters, and…

Customer Question
P0300, p034, p0305, p0306...

P0300, p034, p0305, p0306. NEw cats, plugs, air filters, and maf, injectors ohm out fine.

Mechanic's Assistant: How has your mileage been lately? Have you checked the spark plugs?

Yes plugs are new denso iridium

Mechanic's Assistant: What is the model/year of your Mercedes?

06 c230 sport

Mechanic's Assistant: Are you fixing your C230 yourself? What have you tried so far?

New MAF, Plugs, air filters. I just bought the car and the cats on that side have been replaced recently

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

The #2 02 sensor on bank 2 is showing 0.00 voltage on live data

Submitted: 6 months ago.Category: Mercedes
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Answered in 6 minutes by:
12/31/2017
Mercedes Mechanic: Classic Car Service, Dealership Svc. Mgr. replied 6 months ago
Classic Car Service
Classic Car Service, Dealership Svc. Mgr.
Category: Mercedes
Satisfied Customers: 5,228
Experience: Over 30 years experience in the automotive field
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Hello. Welcome to Just Answer. Please allow me to assist you. We have ran across this issue in our shop several times. I would suggest that you replace the ignition coil assemblies. A P0300 is a "multi cylinder misfire'. The codes P0304, 305 and 306 indicate individual cylinder misfires. More often than not, a faulty ignition coil can cause these codes. I would replace all of the coils; if three are faulty, the others are not far behind needing replacement also.

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Customer reply replied 6 months ago
Number 5 has been replaced very recently, looks almost new, and I replaced the number 5 injector as well. What about the #2 02 on the driver's side showing zero voltage? I have never heard of an 02 causing all cylinders to miss on one side of a motor, but I don't know.
Mercedes Mechanic: Classic Car Service, Dealership Svc. Mgr. replied 6 months ago

Was the replacement parts genuine MB parts? Aftermarket/parts store replacement parts by certain companies are not as good as the genuine ones. The issue with coils is simple. The coils all share the same ground circuit. When the coil is caused to fire, there is a diode in front of the ground circuit to keep voltage from entering the ground. If the diode is faulty, voltage 'leaks' into the ground circuit. This is "read" as a cylinder misfire, even though the cylinder is actually working properly. Zero voltage usually is a bad sensor.

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Customer reply replied 6 months ago
Yeah, but it is not just reading a bad circuit, it is missing like crazy. IT will barely pull itself when trying to accelerate from a stop. IS there a way to test resistance on the coils to see if they are good?
Mercedes Mechanic: Classic Car Service, Dealership Svc. Mgr. replied 6 months ago

It is not a resistance test that you need. Diodes have no resistance. They block current. Here is what you can do. If you can get the codes cleared, do so, and then swap the coils around to different cylinders. take the coils out of 4, 5 and 6 and move them to cyls 1, 2 and 3. If the codes come back as P0301/302/303, the coils are indeed bad.

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Customer reply replied 6 months ago
Ok, I will do that. Is there any possibility that the CPS on the intake came is bad? This is my first time messing with a mercedes, on other cars I have messed with the CAS, or CPS in this case, is the trigger that tells the coil when to fire. Is that a possibility in this situation? Or are the coils and injectors triggered off the crank?
Mercedes Mechanic: Classic Car Service, Dealership Svc. Mgr. replied 6 months ago

I do not believe so you have a CAS or a CPS issue.... You would have CPS and CAS codes, as the crank and cam sensors are monitored for operation and correlation.

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Customer reply replied 6 months ago
this car has 150k on it, I have read about the balance shaft issues that this motor was prone to. Is it possible that it could be the worn balance shaft gear? I would think that would throw a code for cam/crank correlation as well. I don't think that is it because the motor is very quiet, not rattling as one would expect with a worn/stretched timing chain, or worn timing gear.
Mercedes Mechanic: Classic Car Service, Dealership Svc. Mgr. replied 6 months ago

Understood, but, you would have the whole plate of misfire codes if you have cam/crank correlation issues. The balance shaft is in place to counteract inherent vibration. A bad balance shaft gear would not set misfire codes. A bad balance shaft would give you vibration in the engine....perhaps a knock sensor code too. You have neither of these.

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Customer reply replied 6 months ago
I think I figured out the problem. Number 5 has almost no compression. I was reading live data tonight, and noticed that I was getting positive pressure in the intake when revving the motor on the MAP sensor reading. I have spark on that whole bank, and all the injectors ohm out good. I think the blow by is bad enough when revved to induce misses on the two cylinders in front and in back of that one. So, in your experience, what is the most likely culprit? A stuck or broken compression ring? Carboned up valve? Burnt valve? This is the last follow up question, and I appreciate all the help.
Mercedes Mechanic: Classic Car Service, Dealership Svc. Mgr. replied 6 months ago

#5 with low compression? To test rings, add a teaspoon of clean motor oil to the cylinder thru the spark plug hole and retest. If the compression comes up you have bad rings. If the compression remains the same, I suspect a bent or burnt valve, or excess carbon on the valve seats. A can of combustion area cleaner would clean the valve seats. If the engine was ever red-lined, I suspect a bent valve.

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