Mercedes-Benz Forum banner

1 - 20 of 55 Posts

·
Registered
Joined
·
12 Posts
Discussion Starter #1
I have owned my GL 320 from new. On 3 occasions in the last month after travelling approximately 50 miles on the motorway at a variable speed of around 60 to 80mph the power suddenly reduces, it becomes a struggle to maintain 50mph. I have pulled off the motorway and the car over revs and moves forward gaining speed ver very slowly. Pulling over, turning the ignition off and re starting immediately cures the problem, until the next time. The vehicle has just been serviced, there are no warning lights illuninated and everything else appears normal. Any ideas?
 

·
Registered
Joined
·
16 Posts
Toughy

It almost looks like you are loosing boost from the turbo, but pulling over and starting the car again would ( should ) not help it ????
If you would not regain the power ( after restart ) that would mean ( to me ) that there is a loss of charge ( air ) in the intake system and that causes the loss of power, but this does not fit your description. I don't know if too low of pressure would through a check engine light, but someone here should know something about that.
If any of the injectors were faulty check engine would come to play right away....
In my case I have had a loss of power at about 50 to 60 miles an hour, but it was slight loss, no check engine, what I have done was replaced engine fuel filter and air filters, that helped me, did not get the same feeling again ( yet anyway ) I just did it about 3 k ago.
I think that in my case it was something like that, at higher speeds all of the gunk collected in the fuel filter produced enough restriction that it actually slowed me down... It may not be your case, but I think it is worth looking into ( the least expensive thing you can do ).
Hope that helps.
 

·
Registered
Joined
·
92 Posts
From what your describing, sounds like a potential fuel delivery issue. Other question is, what did they just do on the service? Did it start after this last service or has it been there before?
 

·
Registered
Joined
·
81 Posts
I have owned my GL 320 from new. On 3 occasions in the last month after travelling approximately 50 miles on the motorway at a variable speed of around 60 to 80mph the power suddenly reduces, it becomes a struggle to maintain 50mph. I have pulled off the motorway and the car over revs and moves forward gaining speed ver very slowly. Pulling over, turning the ignition off and re starting immediately cures the problem, until the next time. The vehicle has just been serviced, there are no warning lights illuninated and everything else appears normal. Any ideas?
Had the same happen to me. Would not go over 50 and stuck in gear with no warnings or cautions. Dealer replaced charge pressure sensor and intake manifold pressure sesnsor and car is back to normal. When mine did this it would also affect the shifting of the tranmision and shift smoothness. All was attributable to those sensors going bad. Why? Oil intrusion from a leaky turbo is a major player. Mne just failed. Make sure mech looks at the condition of the turbo seals, intake plumbing before you replace the sensors.
 

·
Registered
Joined
·
1,476 Posts
Had the same happen to me. Would not go over 50 and stuck in gear with no warnings or cautions. Dealer replaced charge pressure sensor and intake manifold pressure sesnsor and car is back to normal. When mine did this it would also affect the shifting of the tranmision and shift smoothness. All was attributable to those sensors going bad. Why? Oil intrusion from a leaky turbo is a major player. Mne just failed. Make sure mech looks at the condition of the turbo seals, intake plumbing before you replace the sensors.

Oil intrusion? LOL ALL TURBOS LEAK OIL! THey have to by design! Any mechanic that tells you a turbo is leaking and thinks its not normal needs to stick with rotating tires and leave the technical aspects of the vehicle alone.

The problem was caused by a "Limp" mode being triggered.

THe cause is simply the ECU cutting fueling to prevent the turbo from overspeeding due to a loss of system integrity ie a leak.

Check the pipes from the turbo outlet to the intercooler to the engine. If you have a leak, to protect the turbo, the ECU cuts the fueling to remove the gas energy from the turbo and prevents an overspeed and limits the total output of the turbo hence the severe reduction in power.
 

·
Registered
Joined
·
525 Posts
I'm not clear just how a 'loss of system integrity' (a leak) can fix itself by doing what the OP said: "pull off to side of road, turn off engine, restart and all is back to normal until 'next time'".?:confused:
 

·
Registered
Joined
·
81 Posts
Oil intrusion? LOL ALL TURBOS LEAK OIL! THey have to by design!...

The problem was caused by a "Limp" mode being triggered.

THe cause is simply the ECU cutting fueling to prevent the turbo from overspeeding due to a loss of system integrity ie a leak.

Check the pipes from the turbo outlet to the intercooler to the engine. If you have a leak, to protect the turbo, the ECU cuts the fueling to remove the gas energy from the turbo and prevents an overspeed and limits the total output of the turbo hence the severe reduction in power.
I should perhaps have qualified it with "excessive" quantities of oil being pushed around by the turbo. A fine mist of oil coating the turbo plumbing is normal. Pouring a quart of oil out of your intercooler is not.

There's a root cause for everything. Limp home mode doesn't just happen because the ECU says so. There has to be an erroneous or missing reading for it to trigger LH. In my case, those two sensors were the culprits and while being bathed in oil might destroy one, sometimes they fail for other reasons. Mine did not fail by being oiled to death, and no other reason was given (which doesn't satisfy my quality control process). It is a common fault in higher milage vehicles that have excessive amounts of oil being pushed out of worn turbo seals. Putting sensors into an expired turbo is not going to work for you for long.

Likewise a huge leak in the turbo plumbing. It is a constant and not fixed by cycling power to the engine.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #8
Hi, thanks for the responses so far. The problem ooccured again today, but at a much slower speed after a two hour run. I was coasting down a hill and then went to accellerate, the vehicle revs to around 2000rpm max, and the speed gathers slowly without changing gear, it feels as if the clutch is slipping. Again turning the engine off and an immediate restart cures the problem.
 

·
Registered
Joined
·
81 Posts
Hi, thanks for the responses so far. The problem ooccured again today, but at a much slower speed after a two hour run. I was coasting down a hill and then went to accellerate, the vehicle revs to around 2000rpm max, and the speed gathers slowly without changing gear, it feels as if the clutch is slipping. Again turning the engine off and an immediate restart cures the problem.
It has actually happened to me again, once at low speed after it's been "fixed" by two separate dealers. :mad::mad::mad:
Restart cures the problem.

Question to the OP: Does it happen after you brake?

I'm wondering if has something to do with the brake pedal safety switch that cuts the turbo boost when the brake pedal is applied with some force. I'm going to take a look and see if I can trigger the same symptoms by triggering it without applying brake pressure. Wish me luck.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #11
Car has been fine for two weeks, but the problem came back today. Doesn't appear to be linked to braking.
I did find out today though that reverse gear will not enagage when the problem is present. Again, turning off the ignition and re starting immediately, all was normal.
 

·
Registered
Joined
·
81 Posts
Car has been fine for two weeks, but the problem came back today. Doesn't appear to be linked to braking.
I did find out today though that reverse gear will not enagage when the problem is present. Again, turning off the ignition and re starting immediately, all was normal.
Interesting! Are you at extreme temperatures/altitudes?

I bought a cheap OBD-II code reader and read the codes when this happens (I don't erase them). It threw a P0069 code once (Manifold Absolute Pressure/Barometric Pressure). It's just another data point to have in your hip pocket.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #13
No, not at extreme altitude or temperature. There are no warning lights shown on dash when the problem occurs. Where does the code reader plug in? Thanks.
 

·
Registered
Joined
·
525 Posts
No, not at extreme altitude or temperature. There are no warning lights shown on dash when the problem occurs. Where does the code reader plug in? Thanks.
The data port all OBD readers (and the dealer diagnostic tool) plugs into is located under the dashboard, just to the left of the steering column. It pivots down so that various tools can be inserted. The configuration of the port is standardized by Federal law so that all readers can access the data (although NOT all can do very much with it once it is accessed).
 

·
Registered
Joined
·
81 Posts
UPDATE - New Turbo

Mine did it again two weeks ago. Took it to the dealer with CEL and in failure mode. They diagnosed the turbocharger waste gate was physically stuck open when it was brought in. After a while it would work fine and allow the turbo to charge properly until it stuck open again, resulting in a massive power loss.
Fix - new turbocharger unit, under warranty.:)
The whole unit is non-repairable and comes as one complete unit. Yikes!
This is the third dealer i've taken it too with the same problems, and I've asked the prior two about what they did to eliminate the turbocharger as the root cause. Oh, we tested it.:mad: Those clowns will not be spinning wrenches on my car again.
 

·
Registered
Joined
·
81 Posts
Update 2

After having been through about 8 dealer visits in the last 20k miles due to this power loss condition, here's what I've learned.
-This is an insanely complicated car.
-Any valve in the exhaust/turbo system that doesn't operate properly may cause this condition. This would include the wastegate on the turbo and either EGR valves. Standing by for more mechanical component failures.
-Most sensor codes were red herrings and were caused by the failure of the mechanical component they were attached to.
-The cause for sticky valves could be mechanical, due to excessive carbon buildup. Rarely do the control units go bad, but they can.
-Don't baby the car. Drive it hard from time to time to blow out excess carbon.
-Use quality fuels.
-Take it to the dealer in failure mode. They'll be able to see which valves are sticking. Don't drive it unless you're in an unsafe place.
 

·
Registered
Joined
·
23 Posts
loss of power

i am a mercedes technician and the dealer that i work at have seen several cars with the same complaint. the problem we have found with them are the charge air manifold builds up carbon and shorts out the M55 motor for the flaps in the manifolds. i have a car in now with the same complant and will be putting charge air manifolds on it this week. the engine we are having the problems on are the om642 diesel engines.
 

·
Registered
Joined
·
81 Posts
i am a mercedes technician and the dealer that i work at have seen several cars with the same complaint. the problem we have found with them are the charge air manifold builds up carbon and shorts out the M55 motor for the flaps in the manifolds. i have a car in now with the same complant and will be putting charge air manifolds on it this week. the engine we are having the problems on are the om642 diesel engines.
Bugg,

What do these flaps do? Where is this motor on the engine?
How are the intake manifolds becoming carbonized?
Lotsa questions, thanks for your insight. You may just be the guy to put all these incidents together and enable MBUSA to address the root cause.
 

·
Registered
Joined
·
525 Posts
i am a mercedes technician and the dealer that i work at have seen several cars with the same complaint. the problem we have found with them are the charge air manifold builds up carbon and shorts out the M55 motor for the flaps in the manifolds. i have a car in now with the same complaint and will be putting charge air manifolds on it this week. the engine we are having the problems on are the om642 diesel engines.
This sounds very much like the problem I had last November and had fixed on my dime because car is out of warranty. There are some differences in description that may be just semantics.
The servo motor (M55?) that drives the linkage to the butterfly valve (flaps?) in the intake manifold (charge air manifold?) failed electrically and caused a fuse to blow and all kinds of weird electrical things to happen. Dealer replaced motor and fuse. Dealer did not remove or clean the intake manifold although they claimed to free up the linkage. The engine is the OM642 as above. Sound the same? By the way, I have the failed motor that the dealer removed.
As an aside, the dealer either broke or failed to replace a single hardened steel bolt that holds the charge air pipe between the turbo and the connection to the charge air cooler. This allowed the pipe to shift and the seal around the pipe-to-turbo joint blew out. Because the bolt is hardened the broken piece couldn't be removed from the aluminum manifold. We had just started a trip across country and this stopped the trip cold! Bummer! Car went into the dealer this morning to get it fixed - on HIS dime this time, I hope! They DID give us a GLK loaner (but a gasser :wtf:)
 

·
Registered
Joined
·
23 Posts
power loss

the m55 motor activates linkages in the charge air manifolds controlling the amount of air going into the cylinders. when we have a problem we dont repalce just the motor we replace the whole set of manifolds "it costs more but you want have another problem for a while". The carbon builds up on the flaps and seizes them up and not letting them operate properly.
 
1 - 20 of 55 Posts
Top