ddruker

Over the last couple of weeks, my 2011 GL 350 just has no get up and go at the first start of the day. It's not particularly cold here in California, but I've only seen this happening when the truck has been sitting for a while - and it's not every time.

When the problem is going on, I can floor the accelerator and I get barely perceptible acceleration. Think 0-60 in one minute. If I pull over and turn off and restart the motor, things are normal again and I have the usual power and torque.

There are no codes, no check engine light.

Is this the famous GL "Limp mode" - Anyone seen anything similar or have any ideas?

KrustyKustom

Gotta be a plugged egr valve. Once it warms up it is unstuck...

ddruker

I wrote that last post from the airplane coming home from JFK - kind of cool. Anyway the truck started with the same problem when I got off the plane, so I drove by the dealer and asked them to look at it.

They said the fuel system / injectors were reading funny - but it was 4:30 and they didn't have time to finish diagnosing and I need the truck tomorrow to get our Airstream out to the upcoming Stanford vs. Utah tailgater this weekend.

So I'll suggest EGR to them and let you guys know what it was if/when they figure it out.

N_Jay

No it does not.


It can be any of the many things that put the ECU in to limp mode.


I still have trouble believing that the engineers who wrote the code put in lots of safety traps and did not have them write errors to memory.

KrustyKustom

He said it was not throwing a code?

N_Jay

Yes, I know, mine has done the same thing (as have many others here).


When I said "I can't believe" I didn't mean that I did not believe it could happen, but rather, I meant "What kind of f-ing software architect would design a system with routines to catch error conditions that put the controller into a "safety mode" and not add in a routine to capture the event.


It has been blamed on EGR, MAF, Temperature sensors, DPF filter pressure sensors, Tumbler Flap motors, and a host of other potential issues.


Right now I am betting DPF pressure sensor. Mine does it in cold and wet weather.

ddruker

It is not throwing any codes.

I'm going to leave it at the dealer this coming Tuesday for further diagnosis for a couple of days while I am away at a business trip.

When they plugged it into their computer the other night when it was exhibiting the problem, they said that part of the datastream related to the fuel supply / fuel injector system "looked funny."

And yes - it seems super silly that if the engine control unit knows enough to put the motor in limp mode, for sure it should spit out sufficient data to let a technician know what it thinks the problem is.

N_Jay

Good luck with the dealer. At last yours seems to be happening consistently enough to know when it is fixed.


Mine is 3 to 5 times a winter. Enough to be annoying but too few to start throwing parts at it or to get it to the dealer "limping".


I am thinking about trying the DPF pressure sensor, because it is under the car when it gets wet (part of my symptom) and is a part others have had good luck fixing the issue.

boltonblue

I'll take a shot that it's a throttle position sensor.
My wife's S430 had this issue.
I was driving along and suddenly it lost all oomph but didn't stall.
We were able to get it to the dealer, again no codes or check engine light.
Shut it off, went in did paper work and came back out with mechanic for a ride, and it ran fine.
Sure enough the high side resistor network was faulted.

giffie

Had the exact same issue yesterday with my 2011 diesel. Took it to the dealer and sure enough it was a faulty EGR valve.

drgeeforce

Is the limp mode accelerating up a hill? or on surface streets? What does the dash say? Check engine light? If you get no response from the turbo, then check the fuel delivery, i.e. fuel filter, pump, pickup, sender,etc. Best thing to do is to OBDII query, get a diagnostic. Autozone does it for free. BTW diesel engines don't have a throttle.

N_Jay

Answers from my experience:
Limp mode is reduced power (guessing no, or very limited boost)
May also be a limit in upper RPM.
Hills are only noticed due to needing more power.
Dash says nothing out of the ordinary.
No Check Engine
No dash display errors or events.
I doubt it is a fuel issue as it is sudden onset and completely gone on restart.
Was not able to do ODB test since restart clears issue.
No stored ODB errors from a simple tester.

drgeeforce

Boost is what happens when the turbine spins fast enough to charge the incoming mixture. The lack of boost at highway speeds means the turbine is not turning fast enough to create boost or something is bleeding off the pressure, i.e. wastegate/blow-off valve. The first condition would be created by shifting into neutral at highway speeds where coasting would not produce exhaust gases to drive the turbo. Second is the electronic fuel management is opening the wastegate/blow-off valve decreasing the boost. Common places to look for would be a vacuum leak.

N_Jay

I was under the impression that the boost was controlled by the ECU either (or both) through the control of the variable vanes in the turbocharger or through the control of a wastage/blow-off/bypass valves (or valves).
As such the ECU can greatly reduce or possible eliminate the boost when desired to limit engine power production.


Possibly the limp mode is enforced simply through the limitation of fuel. Anyone KNOW for sure??

drgeeforce

You sir are correct, the ECU controls both the pre and post pressures in the turbo, but a fault in the ECU would trigger a CEL. Fuel starvation as you propose would be felt across the power band, not just at highway speeds.

The Sprinter utilizes a Garrett VVT with vacuum actuator. Loss in vacuum disables the vanes. That will not trigger a CEL.
http://www.mercedes.gen.in/WP35/merc...fault-finding/

Although the most common CEL seen with a turbodiesel with no power is a P0299 Under Boost condition. Default is vanes open.
A few I have fixed with just a spray of WD-40 on the linkage-solenoid transition. Most I have fixed by replacing the vacuum hose to the turbo. Temperatures near the turbo are brutal, hence the aluminum shield.

N_Jay

I am not saying their is a "Fault" in the ECU. MYU guess is a fault in a sensor and the ECU is making the decision to go into "limp mode" either to enforce taking the vehicle for repair or to limit power to avoid other potential damage.
These events are too consistent to be a bug, so I believe it is the intentional activation of specific engine map.
What disappoints me is not storing the code to be easily read upon service.

drgeeforce

Have you corrected your "limp mode" problem? My guess if there's no code being given, then you may have carbon buildup. Once a month or bi-weekly mashing the accelerator pedal to rid the EGR and Turbo of these deposits will help maintain performance. Additives are useless compared to a turbo strip down and carbon cleanup.

N_Jay

I have not had it recur, but have not taken may cold wet drives this year. (We have been cursing in the E)


Why do you think it is carbon?
It has never happened in warm or dray weather.


There is a lot of guessing on this issue, but (again) the most common successful fix has been the DPF differential pressure sensor. (Under the car where it and its electrical connector get cold and wet)

George Philip

my 2010 gl 350 is doing the same...i can floor it and it barely gets past 2 in the rpm gauge...i have to use the paddle shifters to change gears while accelerating otherwise it gets stuck before going up to the next geat...also notice it when slowing down...pedall to the floor and no power like before...did anybody figure out what the problems was

N_Jay

The best guess is the DPF differential pressure sensor.

91stealthes

Agreed, this was my problem when I had the exact same issue.

Franky Sulistyo

Hello, did you find out what was the problem with your car? Can you share?
Thanks!

Franky Sulistyo

Fyi, I have replaced differential pressured and maf sensor and fuel filter and cleaned EGR, but the same issue still exist. I'm getting so frustrated with my GL350 bluetec 2010 since its oil cooler leaking. any inputs from your experience appreciated.

N_Jay

How often and under what conditions is it happening?

alx

has any of you ever read their truck with star/ das? what are the codes? have you observed boost levels at different throttle applied? fuel trim levels?

dont just blindly replace parts...