Help! 2001 W163 ML55 AMG Loss of Power, any ideas?

[leicesterboy15]

Hi All

I hit a problem the other day while coming back from a wedding. Car drove fine on the way there with no power delivery problems but on the way back I gave it the beans off a slip road on to the main road and it seemed to be down on power at higher revs, say about 4k up.

As I continued up the road i could feel the car would not accelerate, it would maintain 75 but you had to push hard to get it to speed up, it would kick down and the revs would rise but still no power, going up hill as well you could feel as though something was holding it back.

So we stopped at the services and the engine was running really rough, almost stalling. I switched it off and turned it back on and all was fine! On the way home you could feel some slight loss of power at higher revs but nothing major (although i didn't push it hard), it felt like the same problem but much less obvious.

Anyone have any ideas where to start looking? Check engine light was on and I will pull the fault codes tonight but I am thinking its electrical, possibly MAF? Are there any usual suspects for issues like this on this car? The car has 134k and is running LPG, I tried it on petrol and LPG but the issue was present in both so I am assuming its not fuel delivery although it did feel like that and I could be wrong!

Any ideas / help is much appreciated!

 

[WG M-B]

It really does sound like you need star. Did the issue originally happen with LPG or petrol?

 

[leicesterboy15]

Originally it happened on LPG so I switched to petrol but it made no difference. After I restarted the engine it ran on petrol for a bit before I switched and it behaved the same on both.

I've just pulled the codes, I could hear a slight roughness on tickover when I got the report below but only slight:

Fault log report generated by Torque for Android
=================================================

Vehicle VIN: Not present
Vehicle Manufacturer: Unknown
Vehicle Calibration ID: 0315454332050002

Current Fault Log
------------------
P0170: Fuel Trim (Bank 1)
P0173: Fuel Trim Malfunction (Bank 2)
P0301: Cylinder 1 Misfire Detected
P0304: Cylinder 4 Misfire Detected
P0303: Cylinder 3 Misfire Detected
P0308: Cylinder 8 Misfire Detected
P0300: Random/Multiple Cylinder Misfire Detected

Pending Fault Log
------------------
ECU reports no pending faults

Historic Fault Log
------------------
ECU reports no historic faults
Other discovered fault codes
(possibly pending, current or manufacturer specific)
----------------------------------------------------
ECU reports no other fault codes logged

End of report.


----------------------------------------------

I cleared all the codes and the car smoothed out after restarting, check engine light also gone. It drove very smoothly after clearing the codes, i took it for a run and it behaved impeccably even on WOT (scary as ever). Got back and the idle is super smooth with no warning lights and no codes!

I fear its the start of something expensive that will only get worse!

I am assuming the star you are referring to is the Mercedes diagnosis? I've got a simple bluetooth OBDII connector and running the torque on my phone. Its pretty good for what it is but its not star! Do you think star would find something different? Any ideas where to start looking based on these codes? Possibly the MAF?

I'm driving to the south of France in August so need to get it sorted by then. My brake servo is also hissing and I need to sort that as well, could this be related due to vacuum leak? Its been doing this for a while and hasn't gotten worse since this problem.

 

[Warrior]

I'm no expert, particularly on codes etc but mechanically if its sucking air from a servo leak i'd guess its likely to weaken the fuel/air mixture leading to the lack of power and misfire?

I'm making a further assumption that the engine sensors will detect this and the ECU will eventually adjust the fuel/air mixture to add more fuel and compensate for the air leak which could be why the fault has now gone?

 

[Steve@Avantgarde]

The fuel trim fault codes I would suspect would say "self adaption" on STAR and that usually points to a MAF failure accompanied by the random misfire fault codes.

 

[leicesterboy15]

Thanks guys, CEL came back on over the weekend and I pulled the codes again, this time I got two errors (log below). After I cleared the codes the idle was sitting at around 1500rpm, when I put my foot on the brake (to stop the hissing) the idle would come back down. After a restart the idle went back to normal, I could still feel that something is not quite right with the power and delivery but its inconsistent.

With the MAF being the cheaper and quicker of the two I will start with that before moving on to the brake servo unless there are any other ideas? If I disconnect the MAF will that tell me anything?

Fault log report generated by Torque for Android
=================================================

Vehicle VIN: Not present
Vehicle Manufacturer: Unknown
Vehicle Calibration ID: 0315454332050002

Current Fault Log
------------------
P0170: Fuel Trim (Bank 1)
P0173: Fuel Trim Malfunction (Bank 2)

Pending Fault Log
------------------
ECU reports no pending faults

Historic Fault Log
------------------
ECU reports no historic faults
Other discovered fault codes
(possibly pending, current or manufacturer specific)
----------------------------------------------------
ECU reports no other fault codes logged

End of report.

 

[Alex Crow]

...the idle was sitting at around 1500rpm, when I put my foot on the brake (to stop the hissing) the idle would come back down...(Presumably back to normal idle speed?)

You only need a small air draw to throw out the fuelling, above you describe a pretty big one.
I suggest you keep your focus on the servo, if what you say above is exactly correct.