Going greyer by the minute - OM646 Intermittent Misfire idle/low revs

[Mintymoo]

Hi All,

I own a 2009 (S211) E220 cdi with 122k and it had a full MBSH up until a couple of years ago. I purchased it in Oct last year.

I changed poly v belt with tensioner and pulleys as was chirping, changed air, fuel and oil filters. Had a cold start issue resolved my new glow plugs & relay.

Fast forward 4 months and the car has developed an intermittent misfire between idle and about 1500 revs. Some days its fine and others it shakes every few seconds while stationary. Its totally baffled me. No fault codes logged and when taken to an indy a for diagnostic they didn't find any problems, charged me for a software update and star session and said to monitor but when I went to pick it up at the end of the day it was chugging at idle. Bast@rd obviously behaved itself while being looked at. The tech came out and agreed something was definetly going on and said that he only noticed that injector 4 was close to tolerance when testing it earlier in day. So £135 lighter and no wiser I went on my way.

I plan on keeping the car for a 3-4 years so took a punt on a deal for 4 brand new Delphi injectors, fitted myself and the overall difference in the engine smoothness, responsiveness and pulling power is astonishing so happy with that.....problem still remained though.

Fitted following (new OE parts)
Fuel leak off lines with Venturi T piece (all one part)
Inlet Metering Valve (Fuel Quantity Valve)
Fuel Rail Pressure Sensor
Fuel Rail Pressure Regulator

I am that now that guy who has thrown parts at the problem after lots of research and still drawn a blank.

EGR was removed and inspected and it must have either been cleaned before or be relatively new because is was remarkably clean for a 122k car, I gave it clean anyway.

My ear maybe deceiving me but I am sure I am hearing noise (whirring and clicking) from the altenator pulley but not noticing the belt jumping?

If I were to notice it happening more when fuel tank is 1/4 full than when it's nearly full would that point to fuel pump?

So come on Mercedes experts, throw the dog a bone here?!

Vacuum leak?
Air entering fuel system plumbing?
Intake manifold gunked up?
High Pressure Fuel Pump?
Altenator pulley/clutch?

Remember, it's intermittent and otherwise pulls like a train and runs smoothley except when this mysterious miss starts happening and then it's chugging with a little smoke and you can feel the car rocking....and then fine again for a few minutes, hours or days.

Any thoughts appreciated guys.

 

[supernoodle]

I would have started by identifying if the issue was always on the same cylinder or not. That would rule a lot of the items in or out.
Injector disconnect when it's happening might give a clue. Even the cylinder balancing data in the diag tool might. If not it would be an oscilloscope on the crank sensor, but that needs a decent auto electrician to know what they are doing. If you put a current clamp on one of the injectors you can use that as a reference.
You're looking to see which cylinder is not contributing.

 

[Doug1234]

As above try to find bad cylinder .. compression check / valve train / cam lobes / cracked head ?/ valve seats esp exhaust

 

[M80]

Do these have a saddle tank, that transfers across the car when the main side is low?

 

[Mintymoo]

I would have started by identifying if the issue was always on the same cylinder or not. That would rule a lot of the items in or out.
Injector disconnect when it's happening might give a clue. Even the cylinder balancing data in the diag tool might. If not it would be an oscilloscope on the crank sensor, but that needs a decent auto electrician to know what they are doing. If you put a current clamp on one of the injectors you can use that as a reference.
You're looking to see which cylinder is not contributing.

Thanks Supernoodle, I have a clamp meter in garage somewhere so

Do these have a saddle tank, that transfers across the car when the main side is low?

Hi M80,

I am fairly sure it does, I've read about the venturi pipe issue whereby the fuel doesn't transfer across from one side to the other but I think I would be getting odd fuel tank readings if it were playing that game. I have asked my wife to fill the tank right to the top and not let it go lower than half for a few weeks to see if that has any impact on the issue. If it does the long search for the culprit could drastically shorten.

 

[Mintymoo]

Thanks Supernoodle, I have a clamp meter in garage somewhere so

Hi M80,

I am fairly sure it does, I've read about the venturi pipe issue whereby the fuel doesn't transfer across from one side to the other but I think I would be getting odd fuel tank readings if it were playing that game. I have asked my wife to fill the tank right to the top and not let it go lower than half for a few weeks to see if that has any impact on the issue. If it does the long search for the culprit could drastically shorten.

For the sake of a few quid on gaskets and a few hours of cleaning I am also strongly leaning toward removing the intake to inspect for carbon build up as at 122k it could well be choked right up. A guy in America who has his own YouTube channel (MBDieselfreak) had a similar issue albeit on an OM648 and his was actually stalling at times. it bugged him for ages until he did some work on the intake swirl flaps and eureka.

 

[Mintymoo]

As above try to find bad cylinder .. compression check / valve train / cam lobes / cracked head ?/ valve seats esp exhaust

Thanks Doug1234

 

[Mintymoo]

A couple of observations this evening.

I noticed that I can replicate the stutter/miss when I manually actuate the EGR valve (see video). I maybe way off piste here but let's imagine the intake on my car is choked up with carbon, poor air flow, swirl flaps not working particularly well etc so o2 isn't as plentiful as it should be but not so bad that it triggers a code....then the EGR through no fault of its own is sitting in the background actuating randomly dumping exhaust gas into an already borderline o2 starved mixture. Is that not grounds enough for an engine stutter?

A second point worthy of mention perhaps is a noise has appeared recently in the v belt area and at first I was starting to consider altenator clutch pulley but the microphone on my phone is at the bottom of the handset so when I put the phone down near the altenator pulley the chirping noise got quieter but lift it up so the mic is near the pulley under the HPFP and the chirping is louder. New continental poly v belt kit, with tensioner and idlers fitted only 6 months ago so this must be one of the more permanent residents. See/listen to vid.

Any thoughts guys?

 

[supernoodle]

If you think it's airflow related check the MAF values in the diag tool when good and bad. In fact check every bit of data you can when good and bad.

 

[cezarrus]

Hey. Did you solved the problem?

 

[cezarrus]

Hi All,

I own a 2009 (S211) E220 cdi with 122k and it had a full MBSH up until a couple of years ago. I purchased it in Oct last year.

I changed poly v belt with tensioner and pulleys as was chirping, changed air, fuel and oil filters. Had a cold start issue resolved my new glow plugs & relay.

Fast forward 4 months and the car has developed an intermittent misfire between idle and about 1500 revs. Some days its fine and others it shakes every few seconds while stationary. Its totally baffled me. No fault codes logged and when taken to an indy a for diagnostic they didn't find any problems, charged me for a software update and star session and said to monitor but when I went to pick it up at the end of the day it was chugging at idle. Bast@rd obviously behaved itself while being looked at. The tech came out and agreed something was definetly going on and said that he only noticed that injector 4 was close to tolerance when testing it earlier in day. So £135 lighter and no wiser I went on my way.

I plan on keeping the car for a 3-4 years so took a punt on a deal for 4 brand new Delphi injectors, fitted myself and the overall difference in the engine smoothness, responsiveness and pulling power is astonishing so happy with that.....problem still remained though.

Fitted following (new OE parts)
Fuel leak off lines with Venturi T piece (all one part)
Inlet Metering Valve (Fuel Quantity Valve)
Fuel Rail Pressure Sensor
Fuel Rail Pressure Regulator

I am that now that guy who has thrown parts at the problem after lots of research and still drawn a blank.

EGR was removed and inspected and it must have either been cleaned before or be relatively new because is was remarkably clean for a 122k car, I gave it clean anyway.

My ear maybe deceiving me but I am sure I am hearing noise (whirring and clicking) from the altenator pulley but not noticing the belt jumping?

If I were to notice it happening more when fuel tank is 1/4 full than when it's nearly full would that point to fuel pump?

So come on Mercedes experts, throw the dog a bone here?!

Vacuum leak?
Air entering fuel system plumbing?
Intake manifold gunked up?
High Pressure Fuel Pump?
Altenator pulley/clutch?

Remember, it's intermittent and otherwise pulls like a train and runs smoothley except when this mysterious miss starts happening and then it's chugging with a little smoke and you can feel the car rocking....and then fine again for a few minutes, hours or days.

Any thoughts appreciated guys.

Any solution that you find?

 

[brandwooddixon]

Welcome to the forum.
The original OP hasn't been seen for almost a year.
If you're having this problem then I'd advise posting a new thread.

 

[cezarrus]

thank you