GarySA

Hi guys,

Can anyone tell me what the max boost pressure is on my S320CDI (OM648)?

The history
I am getting a LIMP mode with no warning lights. The limp mode resets after I turn the ignition off. It happens when I place the engine under heavy load (flooring it or accelerating uphill). The turbo position moves from 95% at idle to about 68% and 1480hPa before it "shuts down" to 10%, and stays there until I turn off the ignition. It used to only happen under really heavy loads but now seems to happen more frequently.

The error code I get is 2348-1: Charge pressure control. Charge pressure is too low.

I have replaced the MAF and MAP sensors.
I have removed the CAT.
I have pressure tested the intake system (from turbo to engine) at 1.5Bar. I used 1.5bar because that is the max I get before the turbo cuts out. It seems to hold that pressure just fine but I am too afraid to go higher until I know how much the turbo should be producing.
I have taken the electronic turbo actuator off and oiled the worm gear. The motor inside turns and only gets stuck at the extremes of the worm gear travel. (will send the turbo in the be tested).

Next on the checklist:
Remove intercooler and check for oil or blockages.
Pressure test boost system at max turbo boost - which I hope to find on this forum.
Send turbo in for testing.

Am I on the right track? Is there something else I should be looking at?

knowbenz

Dont recall max boost but typically see torn intercooler hoses, leaking o ring where the tube meets the turbo, intermittent contact in turbo boost actuator motor causing boost to drop briefly.

ckesswright

OP- Did you end up figuring out your issue? I currently have the same issue with my 2005 E320 CDI.

Rossafuss

I just had the same issue on my 2007 E320 CDI, which has the om642 engine. i also have a 2005 E320 CDI with the om648, the turbo systems are essentially identical, aside from plumbing.

Check your compressor wheels on your turbos gentlemen. Take the intake pipe off, and examine the wheel. If it looks AT ALL mangled, chipped, etc, you will need to rebuild the turbo. to check the inter cooler for blockage, disconnect both sides of the inter cooler, and hook a shop vac up to one end. if you hear the vacuum struggling at all, or don't feel any vacuum on the other end of the inter cooler, you have blockage.

My problem ended up being massive gashes on the back of the rubber hose from the inter cooler to the intake manifold. You could not see them at all, and the gashes were so big you couldn't hear hissing.

ultimately for a low boost pressure condition, it could be one of 3 thing: bad turbo vein motor, bad turbo, or a leak in the plumbing on the PRESSURE side of the turbo. thats about it. A bad boost pressure sensor could be faulty, but if your sensor is sending data in star, its most likely not bad.

Best of luck!

thender21

Your fault code number is flat out wrong. What scan tool are you using?

The charge pressure sensor is located on the left side of the engine on the charge pipe shown in this picture:

http://img.euroauto.ru/photo/parts/u...20371825/1.jpg

Make sure that is the one you replaced.

Inspect the turbo itself and its seals like the other guy said but you also need to check the DPF fill level. A clogged exhaust will cause this type of problem at full load.

If you don't have any charge leaks given everything else you've done you have a bad turbo or a clogged exhaust. I'm leaning towards a clogged exhaust.

Your car has a DPF right? It's a euro model we don't have in the US.

UNderdog

I had intermittent limp mode and overboost and underboost codes on my 2008 GL320. Turned out to be the turbo actuator motor which is only sold with the entire turbo even though it is just bolted-on. This happened at just over 200K miles. You can get just the actuator rebuilt for less than $200 if you look around online and it is an easy remove and replace item. If you remove engine cover you will see the actuator attached to the front left of turbo and it controls an arm which moves the veins in the turbo housing. You can watch the arm move as the ignition is turned on. If arm doesn't move you can disconnect the actuator and if you can manually move the arm (moves very easily) then it should be the actuator that has failed. If arm doesn't move manually after disconnecting the actuator then something is wrong with the veins in the turbo itself. MB turbo unit is manufactured by Garrett and actuator is manufactured by Hella. You can buy an entire new turbo including actuator for a grand or less if you shop around. Dealer list is around $3,600 or so.