LIMP WEIRDNESS

[Fanny]

Sorry for the long story. If you have an idea, would appreciate it. Stuck in UlanBaatar and its getting cooooold!
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History of LIMP mode, loss of turbo.
Krasnoyarsk, Russia (29 July, 231600km), motor shut down on side of highway with EDC dash light. Able to restart and drive (slowly, engine stop if exceed 3000rpm) into MB Krasnoyarsk. Diagnosed problem: 3 leaking injectors. All 4 injectors changed, secondary problem diagnosed: air in fuel lines. No parts available, fuel lines ordered and sent to MB Irkutsk.

During this period, the plastic intake manifold had been removed and reinstalled a half a dozen times.

MB Irkutsk (2 August) installed 1 (of three) plastic fuel lines . Air still present in fuel lines. Not affecting performance of motor. Left MB Irkutsk. Also required removal and reinstalling of the plastic intake manifold.

Left Irkutsk, heading north. Drove approximately 600km on very rough gravel roads. Approached Usk-Kut (8 Aug, 234500km) experienced loss of power. Power degraded in steps over 5 minutes until in LIMP mode driving into Usk-Kut.

From Usk-Kut travelled 7700km on rough gravel roads at low speeds for the next 27 days with motor in LIMP mode. In the first few days, the turbo would randomly work – sometimes for 5 minutes sometimes for several hours – I remember it worked all afternoon one day.

In the next few days, it was possible to reset ECD codes by attempting to start 3x, then TURBO would function for 5 min before cutting out again. After a week, the motor was permanently in LIMP mode.

In 2 instances (in the first week), the TURBO auto engaged at exactly the time it started raining. Turbo functioned for several hours each time.

Arrived at MB Irkutsk (3 September, 243000km, 10000km without turbo) in LIMP mode. Diagnosed low vacuum pressure: verified all the vacuum hoses and connectors. CHANGED: 1)Vacuum Y-connector at passenger side Climate Actuator Valve (dash fan and air recirculation valve), 2)reconnected vacuum hose at rear differential for 4x4 Rear differential Lock, 3) Replaced 1-way check valve at Brake pump leading to 4x4 vacuum pressure tank (pressure tank located under vehicle behind front driver wheel); 4) Turbo Actuator Electric Vacuum Control Valve.

Turbo still not engaging.

Diagnosed fault at Turbo, CHANGED: Turbo and VNT Turbo and Vacuum Actuator assembly
Result:
1. Turbo engages when start in morning first time, or when motor cold and engine started
2. After motor warms to operating temperature, ECM Controlled LIMP mode engaged.
3. Turn off key, turn on key Turbo starts, but LIMP mode engaged after 3-4 minutes.
Observations
1. During diagnoses Test drive with MB Technician (with attached vacuum gauge inside car):
a. Normal operating vacuum pressure~900mbar(?), vehicle vacuum pressure maximum attained was 400-500mbar by MB Irkutsk
b. When vehicle accelerates, vehicle vacuum pressure descends to 150mbar, LIMP mode engaged
c. LIMP mode engaged when engine reaches operating temperature 80 deg Celcius. Loss of boost pressure.
d. RECOMMENDATION MB IRKUTSK: CHANGE MOTOR VACUUM PUMP

Our time limit on our Russian Visa was expiring and we couldn’t wait the 15+ days for the delivery of the vacuum pump. We contacted MB UlanBaatar to order the part timed for our arrival in Mongolia.

Other observations 24 September 2015 leaving Irkutsk driving to UlanBaatar:
We left Irkutsk in LIMP mode for 2 days and drove across the Mongolian border. Camping for the night on 23 September just inside Mongolia border, temperatures dropped to approximately 2 deg C, with overnight snow. In the morning when we left the camping spot, TURBO continued to function. Ambient temperature, according to the exterior temperature sensor reads +0 to +3 degrees, with rain/snow. Driving at low speeds the engine temperature gauge reads 65-70 degrees and the TURBO functions. When accelerating OR climbing hills, the engine temperature reaches 75+ degrees LIMP mode engaged. Stopping the car, turning off the key and then restarting, TURBO functions. Turbo functioned all morning.

It also appeared that if I could keep turbo functioning if I did NOT exceed 70kph (2000rpm). This could be related to engine temperature OR motor ECU sensors.

Stop for lunch, ambient temperature 5 degrees with NO rain/snow. Turbo did NOT work for the rest of the day.

Following day, 25 sept, turbo worked all morning again, not in afternoon. Disconnected all vacuum lines EXCEPT Brake Master Cylinder and directly connected TURBO line to ensure no leaks. NO CHANGE, turbo not working.

***WEIRDNESS BEGINS***
MB UB received the VACUUM PUMP, installs pump. Verifies all lines (again!!! Must be the 5th time).

Turbo works until reaching operating temperature then fails.

Recheck lines. Makes a goofy determination that the problem is the CLIMATE VACUUM ACTUATOR next to fanbox. Of course no parts available, we ‘borrow’ one from another sprinter in the shop.

TURBO works! Drive 120 km with no problems, turbo maintains functioning. (evening/night sunset tour, relatively heavy traffic on moderate roads, ambient temperature +8degC. Able to drive between 50-90kph at random intervals)

Next day, MB UB goes to rear differential to suss out the problem with the rear vacuum actuated Differential Lock. Blablabla the lock is busted, full of dust (from a long since broken line @ diff vacuum mechanical actuator), no parts available. F*** it. Bolt everything back together. Take the car for one last test drive.

No turbo. At operating temperature; loss of boost pressure.

Ideas?
1) Related to bad joint at intake manifold whereby hot expanding motor somehow causes air vent in the intake manifold joint?
2) Airlock in coolant system?
3) Bad head gasket? ( no evidence of this)
4) I’m tired of retesting vacuum lines at MB Mechanic rates and buying parts unnecessarily. This is getting heavy! Next step burn the van.

[Fanny]

Resolved:
1) tightened turbo intercooler hose...not tightened at time of changing turbo
2) replaced/spliced new wire to connection to turbo vacuum pressure switch. Wire partially broken.
3) add 0.5l antifreeze to empty overflow tank.