[HubertPL]

Hi Guys,

I'm new here - I have MB GLK x204, year 2010 with petrol engine 3.0 V6 (272.948).

I got two errors from ECU today (with check engine light) - system too lean (bank 1 & 2) (P0171/P0174 - 0745/0749)

I popped the hood and there was a noisy sound of leaking air (pressure), which came from the back side of the engine. Then I put off the plastic covers of the engine and noticed that this sound came from around of flowmeter (but not from the flowmeter itself). Then I realized also that the engine rpm increased themselves, without touching the accelerator).

Do you knowe from where this leak could come from and what I should do next?

Rgs,
Hubert, Poland

 

[Planethill]

Can you post of picture of the device you believe is making the noise? I am not sure what you mean by "flowmeter"... probably a language thing. Maybe the MAF (mass airflow sensor)?

 

[HubertPL]

Can you post of picture of the device you believe is making the noise? I am not sure what you mean by "flowmeter"... probably a language thing. Maybe the MAF (mass airflow sensor)?

Planethill - indeed - I meant MAF. It is not a noise from MAF exactly but it is close to it and quite loud.

 

[Planethill]

Could be a vacuum hose. There are a couple in that general area. Check them all for cracks or disconnection.

You should also scan for error codes with a Mercedes capable scanner. That will give you a direction to go next.

 

[HubertPL]

Could be a vacuum hose. There are a couple in that general area. Check them all for cracks or disconnection.

You should also scan for error codes with a Mercedes capable scanner. That will give you a direction to go next.

Thank you for the quick response - I will check all of the connections then. Looking for scheme I suppose that there are two main hoses there?
I have checked the errors by AutelMaxiAp200 for M.Benz, I will try to confirm them by something more professional.
Many thanks Planethill, I will let know when I make some progress with this issue

 

[Planethill]

Thank you for the quick response - I will check all of the connections then. Looking for scheme I suppose that there are two main hoses there?
I have checked the errors by AutelMaxiAp200 for M.Benz, I will try to confirm them by something more professional.
Many thanks Planethill, I will let know when I make some progress with this issue

Hmmm. Have you been having any performance or gas mileage issues? If a vacuum leak is large enough to create a "roar", I would think you would feel it when driving. Sluggish, etc. Did your scanner give any leak codes at all? A vacuum leak would definitely throw a code. There are several leak codes (Large leak / Small leak / Really Small Leak / etc). Does the roar happen all the time? Sure it isn't just the air/smog pump? It will roar when on.

Anyway, those codes you reference earlier (p0171 & p0174) usually mean either a vacuum leak or a bad MAF. The baffling part is the "roar" sound. They could be unrelated.

To start, I would remove the MAF and give it a good cleaning with MAF cleaner. Do NOT use anything else, only cleaner designated specially for the MAF. Clear the codes and see if they return. Ruling out a vacuum leak, if the codes return you are looking at a new MAF (in my opinion).

 

[HubertPL]

Hmmm. Have you been having any performance or gas mileage issues? If a vacuum leak is large enough to create a "roar", I would think you would feel it when driving. Sluggish, etc. Did your scanner give any leak codes at all? A vacuum leak would definitely throw a code. There are several leak codes (Large leak / Small leak / Really Small Leak / etc). Does the roar happen all the time? Sure it isn't just the air/smog pump? It will roar when on.

Anyway, those codes you reference earlier (p0171 & p0174) usually mean either a vacuum leak or a bad MAF. The baffling part is the "roar" sound. They could be unrelated.

To start, I would remove the MAF and give it a good cleaning with MAF cleaner. Do NOT use anything else, only cleaner designated specially for the MAF. Clear the codes and see if they return. Ruling out a vacuum leak, if the codes return you are looking at a new MAF (in my opinion).

View attachment 2644738

Genrally, it happend suddenly, with all of these symptoms - 'vacuum air' sound and check with the abovementioned error codes in parallel. Engine has a normal power and acceleration but it shakes at the lower speed, especially when reversing and when standing on 'P' mode increases rpm to 2000 without touching the acceleration pedal.

 

[HubertPL]

Genrally, it happend suddenly, with all of these symptoms - 'vacuum air' sound and check with the abovementioned error codes in parallel. Engine has a normal power and acceleration but it shakes at the lower speed, especially when reversing and when standing on 'P' mode increases rpm to 2000 without touching the acceleration pedal.

[Update]
I have checked all of the hoses connected with MAF - they are all in a good condition and there are connected properely.
View attachment 2644952

Only "leak" which I found could be seen on the photo below (I have repaired it by the tape)
View attachment 2644953

I have also disconnected the MAF and cleaned it properely - but, unfortunately, It has not helped.

Codes are still the same and appears all the time - p0171 & p0174.
Rpm at the parking mode are unstable (sometimes suspended on the higher value) and I can hear some kind of quiet knocking from the engine which shakes a little (movies below). But, at the same time, at the highest rpm car rides and accelerates properly.
Rpm1
Rpm2


So now, I wonder if I should change the MAF ? Or maybe there is a simple way to check the leaks without proffesional smoke machine?

Or it could be also connected with the spark plugs which should be changed also?
I am out of ideas

 

[Witek_M]

So now, I wonder if I should change the MAF ? Or maybe there is a simple way to check the leaks without proffesional smoke machine?

Or it could be also connected with the spark plugs which should be changed also?
I am out of ideas

Vacuum leak needs to be tested with smoke. You may have intake manifold flap stuck in wrong position as well. Car needs to be scanned with MB dedicated scanner.

 

[HubertPL]

Vacuum leak needs to be tested with smoke. You may have intake manifold flap stuck in wrong position as well. Car needs to be scanned with MB dedicated scanner.

Ok, I will try to test the leaks as well as changing MAF - I will have one to replace on Wednesday. Hope this is small and simple issue at all.

ps should I adapt the new MAF - for example by disconnecting the battery?

 

[Planethill]

ps should I adapt the new MAF - for example by disconnecting the battery?

Nope, it is a sensor not a module...so it is plug-n-play.

@Witek_M brings up a good point. The M272 engine is notorious for broken swirl flap linkage. It does not throw a check engine light though, so it can be kind of stealthy.

 

[HubertPL]

Guys,thank you for all of the clues and possible sollutions.
Finally - hose 'part-load breathing' A2720181382 (near the MAF) had been cracked because of contact with the metal part of the lpg injector. It was hard to see, but finally I got it. Now everything is perfect and I have the new MAF also

 

[Planethill]

There you go, that’s full on “busted”! 😆. Glad you figured it out.