Not another LHM/Low Boost Thread

bjlafrance

2006 T1N 158" High Top
Greetings Sprinter Community~
While traveling out to the Northern California Sprinter Campout (Thanks for a fantastic event Dale and all!), my T1N went into a low form of LHM.

Here are a few details:
No CEL, except *sometimes* when I restart the van (even without CEL -> van is in LHM within 5 minutes of clearing codes)
When the CEL does come on, a DAD reads the error as P2526-004, which is a 'right charge pressure positioner' or 'boost pressure regulator open circuit' code.

O2 sensor, Air intake sensor, Ambient temp sensor, turbo hoses, and turbo resonator have all be replaced recently and are properly connected and functioning as far as I can tell. Turbo actuator is not frozen, as I lubed it with Hi-temp lithium grease and can occasionally get boost and see the actuator move before the van goes into LHM.

I've got a Boost Pressure sensor on order from Europarts, and will chase electrical gremlins from the turbo actuator to the ECM to the ground at G202 in the coming weeks. Also FWIW: The van was in a fender bender with the previous owner, but because this error is relatively new, I suspect this isn't a direct result from the accident (perhaps the crash caused a short that took a year to finally appear and cause issues?).
In the meantime wanted to query the forum so see if I could get any other ideas. Any and all recommendations are appreciated
 

sailquik

Well-known member
When did you last have a look at the turbo resonator?
Have you "palpated" (manually squeezed and visually inspected) all of the
turbo hoses?
Have you checked all the turbo plumbing hose clamps?
Does the electronic actuator move it's full range when you start the engine?
Roger
 

bjlafrance

2006 T1N 158" High Top
Hi Roger~
Thanks for the reply!
Checked the turbo resonator this past weekend (its the europarts aluminum 'eliminator')... clean as a whistle with no oil or smudge near the hoses.

Palpated and inspected all the *brand new hoses* when I installed them on sunday... the only hose that hasn't been replaced now is the small 'arm' that stems off the turbo intake hose to the top of the engine, but I inspected that thoroughly as well.

As for the hose clamps... one was missing when I purchased the vehicle, but I replaced that worm gear clamp and checked all the others as well. A second set of eyes (also a t1n owner) couldn't find anything amiss with hoses or clamps.

As for the last question on actuator movement: Actuator does move a bit, but it's not making the full movement compared to another t1n I saw. I'm not sure whether this is the *cause* of the LHM or the *result* of something else that stops the turbo and puts the van in LHM. The fact that I can clear codes or restart the sprinter and still get a couple minutes of boost (i.e. accelerate quickly onto the freeway) makes me think that the actuator arm can move freely along its whole range of motion.

Is it worth pulling the whole turbo assembly and seeing if that linkage freely moves through its entire range? I'm not too familiar with the intercooler, but could a small crack in that also cause a P2526-004 code? Thoughts?
 

sailquik

Well-known member
bjlafrance,
Yes, might be smart to release the ball and socket joint on the bell crank
that extends into the rear (hot/ cast iron) chamber of your turbocharger.
The shaft that the bell crank mounts on is attached to a gear inside the
turbo chamber that rotates to change the position of the vanes that control
your boost/MAP level.
Try some Liquid wrench on the shaft (when the turbo is cold.
Really soak the shaft and perhaps some of the lubricant will "creep"
inside to the gear.
The bell crank should rotate very freely and smoothly.
If not, exercise it manually until it frees up.
Make a couple of marks (Sharpie) at the limits of the bell crank travel.
Then reconnect the linkage and see if the bell crank rotates fully to the
marks when powered by the electronic actuator.
If it still has limited motion, and you continue to have low boost,
you might want to purchase a new/rebuilt electronic actuator.
Can you pull the live data off your DAD unit?
At idle (@ sea level) the MAP should be ~14.7 PSIA (0 PSIG if measuring Boost).
At WOT (Wide Open Throttle) the MAP should be ~ 35-36.9 PSIA (21-22 if measuring Boost).
There are a couple of places that sell reman electronic actuators but they are pricey.
If you have another T1N with the OM-647 engine available you might want to try the
electronic actuator from that engine in yours before buying a new electronic actuator.
Roger
 
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bjlafrance

2006 T1N 158" High Top
Hi Roger~
Excellent info to try. I'll disconnect and check for full movement on the ball crank valve... rain is in the forecast till monday, so it might take a few days to get under the hood and report back. It's an '06 van with only 15k miles, so my fingers are crossed for the vanes inside the turbo being sticky due to lack of use in its neglected previous life.

I was borrowing a friend's DAD, but wrote down the numbers for the boost pressure regulator test. Regardless of the 'Activation Charge Pressure Positioner' being at 0% (Idle) or 95% (WOT, I think), the boost pressure remained at 14-15psi. Not sure if that helps, but it's what I got.
Cheers, Benji
 

autostaretx

Erratic Member
The DAD also has a boost actuator positioning test it can perform .... it runs the actuator from 5% to 95% (and anywhere you ask it).
You can watch the actuator move.

--dick
 

220629

Well-known member
The DAD also has a boost actuator positioning test it can perform .... it runs the actuator from 5% to 95% (and anywhere you ask it).
You can watch the actuator move.

--dick
That is a good test. Even if the actuator moves in the correct range it doesn't take much of a "catch" to affect operation and set LHM.

Just an FIY that gross movement can be ok with a sticking mechanical assembly still being a problem.

For troubleshooting it is likely worth the disassembly that Roger suggests.

vic
 

bjlafrance

2006 T1N 158" High Top
Hi All~
An update as to my Turbo/LHM symptoms based on previous suggestions:

Roger/Sailquik suggested taking apart the bell crank (attached to the turbo fan vanes) and make sure it doesn't catch...
It moves smooth as far as I can tell. My pinkie finger can move it up and down without any effort at all. He also wanted to know live MAP data, which according to my scan gauge and DAD vary between 14PSI and 34PSI based on RPMs. To me, this suggests there is no leak in the air pressure system.

Vic and Dick recommended the DAD for a Boost actuator positioning test...
Whether at 5% or 95% there is no movement. The actuator stays at its 'start' position next too the lowest sharpie mark I made. For reference, this is closest to the earth (most counterclockwise). It does not move up (clockwise) at all. This is also true if I rev the van and don't use the DAD. To me this suggests an actuator issue since the linkage arm isn't frozen, nor are the internal turbo vanes. I'm blown away that the check engine light does not immediately come on, but often takes a few restarts and miles. It seems like the computer would know the actuator isn't moving immediately.

Glad to be zooming in on the root of the problem. I'd like to tear into my own actuator or chase the wiring before buying any big $$$ parts. How easy is this to do?

This post from a few years ago suggests a possible wiring issue and solution:
https://sprinter-source.com/forums/showthread.php?t=35154
I traced the wires from the actuator to the ECM. Everything looks jolly on the surface (I didn't rip open the bundles but there's no visible chafing whatsoever).

Here are a few questions:
Has anyone used a multimeter to check the boost actuator circuitry (easy/hard)? Could I test my actuator on its own, outside of the sprinter? Or perhaps lube the worm gear inside the actuator...etc?

If I must, can I buy just the actuator or do I have to buy the actuator and turbo? The posts on the forum say both, so I'd like a cohesive answer. Related: success rates of remanufactured vs new, and best options for purchase (for a poor graduate student)?

I'll see if I can convince someone the neighborhood to let me borrow their actuator to test... how easy are they to disassemble and transfer?

Keep you posted, and looking forward to hearing suggestions.
Cheers, Benji
 

220629

Well-known member
... He also wanted to know live MAP data, which according to my scan gauge and DAD vary between 14PSI and 34PSI based on RPMs. To me, this suggests there is no leak in the air pressure system.
Maybe. I had a fairly big split in my turbo hose that even while towing my travel trailer up grades would allow very normal pressures... until it didn't.

... I'm blown away that the check engine light does not immediately come on, but often takes a few restarts and miles. It seems like the computer would know the actuator isn't moving immediately.
Historically small air leaks can set LHM and not trigger the MIL aka CEL. The ECM monitors actual air flow as compared to expected during engine operation. The ECM aka ECU may be very aware that the turbo actuator isn't moving because it may have disabled it for LHM.

To be clear, I'm saying that you have an air leak, just that the turbo operation can be intentionally disabled without seeing the MIL aka CEL. There are many different levels of LHM. Some just limit engine rpm. I've always said that Mother Mercedes should give us an "LHM Set" dash indicator. That would save a bunch of guessing.

...If I must, can I buy just the actuator or do I have to buy the actuator and turbo? The posts on the forum say both, so I'd like a cohesive answer. Related: success rates of remanufactured vs new, and best options for purchase (for a poor graduate student)?
You may not get that answer. As you mention, MB states that the actuator shouldn't be replaced separately. It has been done with apparent success though.

...I'll see if I can convince someone the neighborhood to let me borrow their actuator to test... how easy are they to disassemble and transfer?

Cheers, Benji
I'd be concerned that in doing that a perfectly good actuator may be damaged or the factory settings could get messed up.

vic
 

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