Have you pulled and read the codes? It could be a faulty voltage regulator ( flickering lights on acceleration )or a vacuum leak (sucking sound). That's the first place I'd look. Good luck.

 

Codes timeline
1. MAF - Replaced - No difference
2. EGR - Cleaned/Checked/Electronically Tested
3. Random and specific misfire codes coupled with very noticeable reduction in power - Discovered faulty coils, replaced them - Power back up but this issue in this topic still present.
4. I'm seeing an MAF circuit code which suggests to me that there might be a problem with the wiring in that circuit.

Is it possible that all of my problems are as a result of this main one? I think it might be a vacuum issue too but my main problem is how do I go about checking (not repairing) something like that on my own? Mechanics here are entirely unreliable because they're more interested in carrying out as many lucrative repairs as possible than actually solving the problem. And it is almost impossible to have a conversation with them about what you think the problem is. They will want to do silly things like replace spark plugs/coil packs again just for the profit.

Can you please explain how such a leak would happen, where it might be and a simple way to check? I prefer to have a very good understanding of the problem before going to one of these guys so I don't get robbed.


(I don't think it's a voltage regulator because that light issue only happens during that brief period where it seems to have lost most of its power. I think it's just a side effect of the power loss.)

 

What lights are flickering, the Instrument Cluster lights or the headlights or both. Post another video of that.

Is the CEL on?

 

@43sqd its too bright at the moment to see the lights (its most obvious with the interior cabin lights) dimming but it's the same kind of dimming you get when you start the engine while they're on. I also realise that 'flicker' may have been the wrong word, sorry about that. CEL is still on, I haven't done anything about the MAF circuit so that makes sense.

 

Do you have a scanner, not a code reader?

What are the code numbers, precisely?

Are these interior lights dimming while a door is open?

 

Interior lights are not dimming while the doors are open.

I think what I have is somewhere in the middle of a scanner and a reader but most of the diagnosis was done at a workshop where the electrical guy there has an elaborate scanner. He was able to test the EGR actuation and other such things to find out the bad coils were causing the misfires. I replaced the dysfunctional coils already (their price quote was more than triple the cost of buying the coils myself WITHOUT labour) and the engine power is more or less back to normal, just this 'pressure' problem left.

I will get my reader and read the codes now as well.

 

P0100 - Mass of Volume Air Flow A Circuit
P0302 - Cylinder 2 Misfire Detected
P0304 - Cylinder 4 Misfire Detected
P0300 - Random/Multiple Cylinder Misfire Detected

I haven't cleared them since I replaced the coils but it definitely feels like they're no longer misfiring.

 

Some 'Live Data' from idling

O2 sensor output voltage Bank 1 Sensor 1 - 0.15V
O2 sensor output voltage Bank 1 Sensor 2 - 0.05V
O2 sensor output voltage Bank 2 Sensor 1 - 0.77V
O2 sensor output voltage Bank 2 Sensor 1 - 0.75V

MAF - around 6 g/s

Fuel System 1 - OL-Fault
Fuel System 2 - OL-Fault

RPM - around 700

MAP - 37 KPa

Location of sensors - B1S12--B2S12

Short term fuel trim bank 1 sensor 1 0%
Short term fuel trim bank 1 sensor 2 N/A

Short term fuel trim bank 2 sensor 1 -0%
Short term fuel trim bank 2 sensor 2 - 99.2%

 

Idle TP - 2.7%

Calculated load value 24.7%

Sorry hit send too soon, can't find an edit button

 

After you post, you can edit that post by clicking on the EDIT button.

 

On your scanner you must look through the menu and monitor all six cylinders at Misfire Fault Counter. First at idle and then at 2,500 RPM's.

Post back with any cyl. that has a misfire.

Do not clear any codes.

 

Can't find a misfire fault counter. The misfire DTCs have disappeared too, I just scanned again. Just the MAF one left. Also, there's an intermittent popping sound coming from the right side of the engine around that area where the battery is. Every time the sound happens, it coupled with a slight but noticeable drop in the engine noise. With the engine off but ignition on, there's a high pitched noise also coming from that general area.

EDIT: The popping sound isn't audible in a video, I just tried recording it.

 

Even though it has nothing to do with your problem, but the video sounded like you had a power steering whine.

 

I do have a power steering whine! How did you hear that? I'll have someone take a look at it.

But what are your thoughts on the main problem?

 

I had a similar issue previously (non merc) that caused same drop in revs on acceleration and a dip in electrical power (presumably due to low revs on alternator). It turned out to be one of the vacuum hoses (had perished underneath allowing escape of pressure). It even caused the engine to occasionally stall at idle, and caused a bit of a rough idle with what sounded like racing between advance and retard. May be worth getting the vacuum lines checked as perhaps one got crushed or dislodged during your accident and may not be sealing. (I do not know your engine by the way)

 

In the "old days" we'd hook a vacuum meter to a port and watch for variations or needle " flutter". The vacuum if I recall should be up at the 12 o'clock position (sorry old age and a lack of a meter prevents me from giving the accurate reading) and stable with it dropping off momentarily on acceleration and returning rock steady to the prior reading. If it's low or is fluttering you may have a broken or split vacuum line. Good luck.

 

@43sqd any chance you might be able to help me with inspecting for a vacuum leak? My problem is exactly like what @th3h1ghlander described. Also, is it something I would be able to do myself? I'm no mechanic but I'm willing to poke around and learn.

 

If you search the forum, you can find several threads with photos and diagrams of vacuum hose locations, like this one: http://www.benzworld.org/forums/w16...63-m-class/1656608-brake-booster-vacuum-line-connection-engine.html#post5284403

Use a mirror.

 

Any luck checking the hoses?


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I checked them all and found nothing. I had a professional take a look too. I forgot to mention this before but sometimes I get feedback from the brakes like there's air being forced out of something. And there's another sound of a flap or something like that being forced open/closed during acceleration. Both things are definitely happening around the area where the pedals are.

 

I am just guessing, but it sounds like your brake booster has lost its seal.
It would account for all the symptoms you added about noise around the pedals.

 

I've done some reading about this online and I think so too. Will I really have to replace the entire thing? Also, how easy is it to check that the seal is gone?

 

Some people have resealed it, but there have been more failures than fixes trying that.

If it were my ML I would replace it as a long term fix.

 

The booster sits behind the master cylinder against the firewall.

 

Replaced the brake booster, no difference in the driving experience. Thoughts?

 

At your mileage it is common to have cracks or splits in the plastic air intake hose between the MAF sensor and the throttle body. This would allow unmetered air into the system and create a sucking noise. Check yours.

 

The problem is exactly the same with the MAF sensor disconnected, doesn't that imply that the MAF is not responsible? Also, the current MAF is a replacement from a few months back from Bosch.

 

Most probably part# 158 is not sitting properly on part # 80. Push it in properly while the car is on & the sound will disappear.

 

Apparently its not so easy to get to that part of the car. Do you have a guide on taking some of the air intake stuff apart so its more easily accessible?

 

You don't need to take apart anything. Stick your hand to the back of the engine. You will find the part. It is next to the EGR tube. While the engine is running push it down. The hiss will stop if that is the cause.

 

Tried feeling around back there for ages, couldn't find anything that would even move -.- I'm sure it's because I'm bad at this too. Any tips?

Oh and does the engine need to be on? I think my first dilemma is locating the EGR tube, what number is it on that drawing?

 

The part 158 is in the red circle. From either side of the car, you will have easy access to it.