New turbo – still no boost! Mercedes Sprinter

 
A Mercedes 4 cylinder Luton body vehicle came to me with a turbo boost problem.  The owner complained that when driving it felt like it had lost all the boost.  On gentle acceleration it was drivable, but under any real load it did not produce any power to speak of and smoked from the exhaust.  The history of the vehicle was that this fault had been occurring for a month or two prior to the turbo failing catastrophically on the motorway.

I checked all the hose work and intercooler for problems with leaks or splits and nothing obvious was found.  A shiny new turbo was present under the bonnet (hood) and looked to be functioning correctly.  The vane actuating lever was moving under engine load and all looked well with the vac control valve, vac supply pipes etc.

A quick read of the ECU with the code reader showed that there was a low boost fault code stored (no surprise there!)  Selecting the live data view on the code reader revealed an atmospheric pressure of 990 mb and a boost pressure of 1010 mb at idle, on a test drive under load the boost produced did not rise above 1150 mb (absolute) , sure enough no boost but why?  I made sure the % on/off signal to the actuator was calling for full boost at this point on live data just to confirm it was not being told by the ECU to apply this amount of low boost.

I had previously mentioned the vacuum lines that feed the turbo boost controller were good and the feed line to the actuator itself was perfect.

As normal, once started, the lever of the turbo vane actuator dropped just as it should to charge position at idle.  I moved the actuator by hand and noticed that although the lever was pulling down under vac, it was not pulling fully down, there was a good 6-8mm of travel left in the lever at its maximum actuated position, though it could be pushed down yet further to its ‘mechanical stop’ with a screwdriver.

My first thought was: there was not enough vac available to fully actuate the turbo – not the case.  Was the turbo boost actuator valve faulty? – not the case. Vacuum actuator diaphragm holed or leaking – no as it held perfect vacuum.

Mercedes Sprinter Turbo Rebuild

Undo the lock nut on the actuator rod (yellow painted here) to the right of this is a knurled adjusting wheel. Adjust to set the required rod lenght (Until a full vac condition holds the vane lever to its maximum on the mechanical stop)

After a while it occurred to me that the reason the vane lever on the turbo was not being pulled down enough was the fact the turbo actuator was at the end of its mechanical stroke.  Removing the small circlip on the actuator rod eye and removing it from the turbo vane lever I was able to adjust the length of the arm. This was done by slackening the 10mm lock nut on the rod and screwing the knurled adjuster, shortening the rod length. This allowed the rod to now pull the lever fully down onto its mechanical stop under full vacuum stroke.  The small circlip was replaced and road tests carried out.

We had now regained the lost boost, the van pulled like a train in all gears. Success!  Since the van had recently had a new turbo fitted, obviously no adjustment had been carried out to the actuator stroke, it was just swapped over from the old turbo to the new one.  After correct adjustments, road tests proved max boost was in the normal range (2447 mb absolute / 21 psi) and expected performance restored. I suppose the moral of the story here is never assume that just changing the turbo without correctly setting up the controlling actuator stroke, will work out of the box.

I hope you find this cautionary tale informative and it may just draw your attention to this issue should it ever pass your way. NB. The reason the fault was noticed before the turbo blew and was replaced with the new unit was because: The old turbo was failing and could not produce useable boost – Same issue and symptoms (no/little boost}, just different totally different causes!

8 thoughts on “New turbo – still no boost! Mercedes Sprinter

  1. Hi
    I have had a weird issue with the turbo on my 2003 sprinter where the turbo stops working after a while. various mechanics have tried but with no success.
    the turbo can be rebooted by turning off the ignition then back on again. the turbo will then work fine until i take my foot off the accelerator and the revs drop.

    1. Hi Phil,
      First place to look is the actuator. Make sure it’s holding vac and is not sticking at all. It sounds like it’s applying boost but is not cutting it when decelerating. Causing an overboost situation.

      Also be sure the boost vac control actuator is not faulty as this is a common area of failure.

      There is a chance the turbo vane mechanism is coaked up and sticking too, so remove the actuator linkage and ensure everything moves freely back and forth.

      Hope that’s some help.
      All the best
      Steve

  2. J’ai un sprinter Mercedes Benz 2003 moteur 2.7 lorsque j’accélère toute cesse de fonctionner,je redémarre le véhicule tout va bien mais au moment de l’accélération a environ 3500 rpm tout cesse de fonctionner.si je démarre le véhicule et actionne l’embrayage et le laisse prendre son accélération sans toucher à la pédal d’accélération le moteur ne s’éteint pas mais au moment que je désire accélérer tout cesse de fonctionner . Où est le problème ?

    1. Hi Ghislain,
      Salut, Si je comprends bien, le régime du véhicule sur son propre sans appuyer sur la pédale, alors il pourrait être un défaut capteur de position de la pédale d’accélérateur (unité de pédale). La meilleure idée serait d’obtenir la camionnette sur un lecteur de code OBD mercedes et voir ce que les codes défaut donne – ce qui est le meilleur que je pense que dans ce cas.
      Rgds
      Steve

  3. Hi there Steve, I have this exact!!! same issue. We started though by replacing very costly parts like injectors, egr valve, actuators, replaced sensors, checked vacuum hoses, to no avail.

    I have a 2012 MB Sprinter 515CDI with an OM651 engine in it. After more than a year struggling with this problem, I am at my wits end. Originally we removed the turbo and had this inspected by a local turbo clinic – “nothing” found faulty. We thereafter replaced 3 sensors, the boost pressure sensor, exhaust gas temperature sensor & O2 sensor, neither of which stopped the above fault code from reappearing in ECU memory and causing the vehicle to enter limp mode very quickly. We then considered that the injectors were not causing correct atomisation in various cylinders to create the correct gas mixture and give proper boost, thereby causing a sensor failure, this coupled with the fact that at startup we could hear an injector making a sort of ticking noise when cold and at initial pull off (spluttering/sort of slapping), but only when cold – we therefore used a delphi diagnostic unit to subsequently read the correction rates on the various cylinders and noted that 2 were over corrected to a large degree when at idle and when test driving at various revs, we then replaced & recoded 2 injectors – this corrected, the overall running of the engine when cold, and pulling off improved (no spluttering) but it did not fix the boost fault given above. We thereafter decided to replace the EGR valve on the vehicle as we noticed once the 2 injectors were replaced – when driving, that when the vehicle wanted to boost occasional plumes of black smoke would come out of the exhaust intermittently, but only since injector replacement, this never occurred before. Too my dismay, replacing this EGR valve has not corrected the problem, the vehicle still goes into limp mode. I have no idea where to turn to at this stage as this is very much a trial and error problem at the moment as i believe it to be quite a unique fault. I’ve had it at a Mercedes-Benz dealership locally but they have been unable to diagnose and correct the problem and leaving it in their hands will just result in the same scenario we have gone through but with the added cost of the labour to our bill. Any help here from anyone would be greatly appreciated. PS. We have also replaced and tested the 2 pressure transducers that the turbo uses for wastegate control and for the boost pressure control flap without any joy. That we are aware of, there are no leaks on the vacuum hoses but we are unsure of how to correctly test this, except to say that when at idle, disconnecting of either of these hoses from the turbo will cause the various actuators to open/close. Could this fault you explained above be the fault or could the turbo guys have missed something within the turbo like a shutoff valve/port that may be burnt away inside the turbo etc? When driving it, you do on occasion get boost but intermittently but not on every occasion as when boost is not achieved the ECU will kick the engine into limp mode and then only switching off the engine and restarting it will correct this….for a short time until boost failure occurs again, which is pretty quickly. Any help here would be greatly appreciated.

    1. Hi Warwick,
      You have spent some brass! I would be looking to make sure the linkages or intake swirl flaps (if fitted on this 515 – should be) were doing their job correctly and that the flaps themselves were still in one piece and not broken or jamming the inlet tracts closed. It is common if the actuator is still moving correctly for the ECU not to report a problem as it thinks all is well. The composite 651 inlet manifolds are prone to mounting stud/flange problems and what happens is the clamping force of the bolt pulls through the insert in the composite and it becomes impossible to seal, turbo pressure escapes past the faces and out you go into limp home. If you have not done it already take of the inlet manifold and give it a damned good look over, flaps and all. I really don’t know what else to suggest as you have pretty much replaced the lot!! The pluming of black puff when you call for power is unburnt fuel, signifying restricted or reduced combustion charge air. Either from a leaking or obstructed intake manifold.

      Hope that helps
      Steve

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