M275 possible O2 issue

[mrmb]

Hey Guys,

I am still experiencing missfires on my M275 on the right bank mostlu cylinder 10/11/12

I have new coils, new spark plugs and brand new voltage transformer.

Here is the test of the O2 sensors. I don’t think they look correctly.

 

[LostKiwi]

I'm guessing you have 2 downpipes, each with a sensor pre and post cat.

If so and you have a misfire on 10,11 and 12 I wouldn't be suspecting the lambda - I'd be looking at the manifold and pipework for air leaks.

If you have a lambda fault it will affect the entire bank (unless 10, 11 and 12 have a separate cat and sensors).

If you pull the plugs on those cylinders compared to the rest?

 

[mrmb]

Can you point me a towards air leaks on the manifold? In fact I have done the test under full load and it looks like the pressure cannot be build up correctly. Any time I will try to pull harder it just throw an engine light with missfire damagin TWC. I have replaced both sensors to brand new Bosh. They are reading good pressure while idling. I wonder if it could be a diverter valve on feont of the engine that is connected to the charge air distributor line separating pil is well. It would make sense.

 

[mrmb]

I have just notice that I did not performed the test properly. On the USA forum I have found a similar topic and people over there they have replaced an Air Valve/Oil seperator - part number is A275 010 02 91

I should have the part at the end of this week. What else could cause missfire? Could it be fuel filter?

 

[LostKiwi]

You have 12 cylinders, 9 of which are not showing a problem. The problem cylinders are grouped together. This suggests a localised issue which will probably be a physical one.
You need to look at things that will affect those three cylinders and only those cylinders. Components common to all cylinders can be pretty much ruled out.
So what vacuum take-offs are there on the manifold for cylinders 10,11,12? Is the coilpack good (its a single pack so could be damage to one end or they may share a common component on the circuit).

A component used by all cylinders will almost always affect all cylinders (MAF, pressure sensors, fuel pump, fuel filters etc). O2 sensors are per bank so will affect half the engine, injectors are per cylinder so affect a single cylinder (though the fuel control feedback can make this problem affect a whole bank).

 

[Oldspanners]

I have just notice that I did not performed the test properly. On the USA forum I have found a similar topic and people over there they have replaced an Air Valve/Oil seperator - part number is A275 010 02 91

I should have the part at the end of this week. What else could cause missfire? Could it be fuel filter?

A weak mixture could cause a misfire because of a faulty O2 sensor.
Have a look at this video it explains it.

 

[mrmb]

Thanks guys for the reply. I know from the other forum that people also had a faulty O2 sensors and they were causing missfires on the last 3 cylinders - I have no idea how this is possible. One coil pack is brand new, the other is from v12icpack in states. It is working fine. Iginition Coil Packs, Voltage transformer etc. all good 100%.

Looking at the O2 sensors itself can you see anything irregular that would show there might be a problem with them? I do not know if this is correct but I was told that two O2 sensors after the exhaust should show the steady line where the other two O2 sensors before catalic converter should fluctuate? Is this right?

 

[Oldspanners]

Thanks guys for the reply. I know from the other forum that people also had a faulty O2 sensors and they were causing missfires on the last 3 cylinders - I have no idea how this is possible. One coil pack is brand new, the other is from v12icpack in states. It is working fine. Iginition Coil Packs, Voltage transformer etc. all good 100%.

Looking at the O2 sensors itself can you see anything irregular that would show there might be a problem with them? I do not know if this is correct but I was told that two O2 sensors after the exhaust should show the steady line where the other two O2 sensors before catalic converter should fluctuate? Is this right?

Watch the video in the link I posted.

 

[alexanderfoti]

On M275 engines, its very important to determine the characteristics of the misfire.

Your fault is unlikely to be O2 sensor related. Check your long term and short term fuel trims. If they are pegged on one bank, then maybe you have an O2 sensor issue. The inlet manifold is shared between all cylinders and does not tend to leak on these unless disturbued.

You are correct, pre cat O2 should switch rich/lean like that, post cat O2's should be a flat line (if the CAT's are working correctly)

You could have an injector issue as well.

Under what state does it misfire? Does it run on 9 cylinders straight after its starts, or does it run on 12 then drop down to 9 after 30 seconds? Is it only under load that it msifires? etc?

 

[mrmb]

On M275 engines, its very important to determine the characteristics of the misfire.

Your fault is unlikely to be O2 sensor related. Check your long term and short term fuel trims. If they are pegged on one bank, then maybe you have an O2 sensor issue. The inlet manifold is shared between all cylinders and does not tend to leak on these unless disturbued.

You are correct, pre cat O2 should switch rich/lean like that, post cat O2's should be a flat line (if the CAT's are working correctly)

You could have an injector issue as well.

Under what state does it misfire? Does it run on 9 cylinders straight after its starts, or does it run on 12 then drop down to 9 after 30 seconds? Is it only under load that it msifires? etc?

When we start the car you could see it is running rough. When I will do the test to check smooth idle running I can see that cylinders 10, 11, 12 and ometime 9 and 6 are running rough however 9,6 will get maybe 3-5 detected missfires where 10, 11, 12 will get 12-20.

You can feel on the sit that it is shaking. When you drive you don't feel missfires at all. When you will floor the throthle then I am getting check engine light and the engine is not running right. After stop and start it is back working as it was after start on cold. I have checked injectors by switching them off each time and I could see difference on each injector. I will see if I can check injectors quantities on the SD.

I will the valve on Friday so I will replace it and check it. If there won't be any improvement then I guess I will have to check the injectors. Can you actually swapthe injectors between cylinders just for the test?

 

[alexanderfoti]

You can swap injectors between cylinders but its a lot of work. I have had instances of them getting stuck open and dribbling.

If a cylinder is completely misfiring, the fault counter will be 50+ very quickly. 0-20 is relatively normal and not something I would chase.

 

[mrmb]

I will check the valve and eventually I will replace the spark plugs on these 3 cylinders but they were replaced like 15 000km ago all of them

 

[mrmb]

Small update today. Yesterday we replaced that valve. Stranegely when I have started the car it seemed to be running fine and then after a short while I started feeling rough running. On the test graph for pre cat oxygen sensors I have notice that it is responding slower than the left bank of cylinders 1-6. Right bank pre cat oxygen sensors is responding every 2 seconds which is double of what left bank is responding with. I have ordered a new pre cat oxygen sensor. I know I am going blind currently. After this the only thing to check are the spark plugs on these cylinders: 9, 10, 11, 12

Igintion coil on the right bank was bought from v12icpack. I have sent the previous one to him and found that the last 3 cylinders had a bad mosfet on them. He shipped a new repaired coil to me but there is the same sympton. He also checked the voltage transformer and said it it is good is well. I have no more ideas why only these 4 cylinders would missfire. Engine was running great up until some point. It cannot be wear in the engine as it has only 130 000km on the clock and it was well minded. We got the car with about 70 000km on it.

I am waiting now for the oxygen sensor and fingers crossed this will cure my issue. If that would be a fuel filter it should affect all cylinders not only 9, 10, 11, 12. I will also check fuel pressure on the rail, however from what I have remember I have done this already :-D

 

[alexanderfoti]

Is it rough running/misfiring at idle in drive?

 

[mrmb]

It missfires at idle. When you drive gently it seems that engine is running fine. When you revit up, check engine light and limp mode. After stop and start it missfires at idle but drives ok if you will do it gentle. It has power etc. I will plug in SD today is well and do few checks again. Can you tell me from your point what you would check on SD?

 

[Steve@Avantgarde]

All this tech info and guess work and no one has actually put the fault codes up?

 

[mrmb]

It is a P0300x so it is a general fault code about missfires. I happens on 2-4 cylinders :-( Also from time to time it will throw a fault code related to TWC (Damaging TWC) When I saw the code related to TWC I have started looking into oxygen sensors. from previous checks I can see that pre cat oxygen sensor on right bank for cylinders 7-12 is responding slower than the one the left side.

 

[Steve@Avantgarde]

It won't be your O2 sensors. They are monitored by the ECU using voltage and signal. You can test each sensor with STAR for actual value (like you have done with your graph test) as well as measuring the internal resistance of them to test them for serviceability. STAR will give you the values via guided test.

Also, your misfire is being caused at spark ignition, not in emission value. The clue is in the code itself. Hard misfire on cylinder XXX. If it was an emission fault causing misfire you would have a self adaption running fault code(s) stored. Likely affecting both banks and erratic misfire counts on the smooth running test.

Have you done a smooth running test with STAR to pinpoint the fault count on the cylinder? If so which cylinder counts the fastest?

Have you tested the high voltage spark transformer ECU for signal output? Very common on this engine.

At the moment you are guessing at components failing with no evidence. Diagnosis is about testing the components for operation rather than condemning them on information that you expect to see.

For example, you state that the pre cat O2s are out of spec, well you have a misfire, so the actual value they are measuring is different to spec, that will show on your graph, and yet you have no fault code to suggest your O2s are failing and you haven't actually tested them with a multimeter to prove they are faulty either, so why are you thinking to replace them? It doesnt make sense.

The combustion misfire fault code you get on star has a guided fault finding procedure on it. Follow it, it will lead you to the fault.

 

[mrmb]

I have done more troubleshooting. The most affected cylinder is cylinder 10 where it can get up to 15/20 missfires in the course of 1 minute. Cyliders 9,11,12 will get only few missfires such as 4/5. I have also notice that left site started getting some is well which makes me crazy. There is a brand new coil in cylinders 1-6 and voltage transformer from v12icpack that was also checked and confirmed it is working. Spark plugs are new is well as they have around 5000km. I bought them from Mercedes and it looks like they were iridium NGK spark plugs.

Car was tested on emissions and they are perfect. I was talking to one of forum members in USA and he told me he had exactly same issue as mine, everyone were saying that O2 sensor cannot cause this and tests were showing that everything is fine. I took a chance and ordered an O2 sensor, I will fitted during the weekend as I am still waiting for the package and I will let you know.

I have also noticed that pre cat O2 sensors on one of the tests on SD did not change voltage to the lower section where it should and it was switch on so this might be an indication of it. I will test the old sensor with voltage meter.

 

[mrmb]

Ok I have replaced one O2 sensor on the right bank for cylinders 7-12 - no change I have checked fuel pressure and I am getting around 4 bars, it fluctuates a bit 3.8-4 bars. According to the training manual it is a good pressure. Is this good?

I wonder where to look next? Fuel injectors? Intake leaks?