Turbo loss without dash light on 2002 t1n - the vacuum tube scenario

VanHausen

New member
So this is a bit of a write-up on probably the most annoying problem I've had to date. Some of it overlaps other threads, but I had some trouble getting all the bits together and filtering out the extraneous stuff about EGR and resonators than don't apply in this case, so I'm trying to put the whole process in one place.

Background: 2002 Australian 4 cyl OM611 in good nick, with 200 k on the clock. One day, mid-trip, it lost what seemed like 3/4 of its power, with no dash lights or codes on either ScanGauge.

It would take off in 1st, but once moving, foot to the floor, I'd get a deeper, almost 'burbling' rumble from the exhaust, and nothing in mid to top end. Max 90kph, forget about hills. Curiously, cycling the ignition fixed the problem....for a day. Then an hour. Then a few minutes, then not at all. ScanGauge showed MAP (manifold pressure) was ~ 115kPa ie basically ambient. So the turbo was the culprit. But how, and why?

Being ignorant and in a hurry, I took it to a certain well reputed Sprinter specialist here in Australia. "Yeah nah mate, turbo's had it, they go all the time, it'll be bout a grand ". After insisting a dead turbo isn't fixed by cycling a key, they compromised saying they'd hook up the computer for a diagnostics run.

Instead got it back the next day, with a $300 bill for what I know now to be a new (well, 2nd hand) turbo vacuum actuator solenoid. No diagnostics readout, no codes, no explanation on how or why they came to that conclusion. But it ran, sortof OK, for about a month, sporadically repeating the recovering, until once again the turbo dropped for good.

For obvious reasons, I didn't go back to that mechanic, but instead found this thread, and subsequently this thread.

Not having any diagnostics computer, ordered one off ebay, and while waiting, I pulled the solenoid and tested the resistance across its two pins. 14.6Ohm on the meter. Hm. There goes that theory.

Then I tried bypassing the solenoid, by jumping the vac feed hose at idle, straight to the actuator hose. Or in plain speak, plug blue-arrow hose into yellow-arrow spigot after removing small bent hose (see pic - 'vac solenoid').


Oddly, this produced no movement on the turbo actuator arm (see pic 'turbo') at idle but it DID move the arm when I turned the ignition off. A calibrated finger test on the spigot confirmed - no vaccum with engine running, but temporary vacuum once it stopped. WTF?


The I found this this thread. Repeating their test, I plugged the vac line output that goes to the actuator for closing the cab air vent intake (see pic 'vac lines'). Hey-ho, the turbo actuator sprung to life at idle.

Tracing the vac line to the cab air vent actuator (above the battery, rhs of cab air intake), I found the true problem immediately - one of the vac hoses for the actuator was attached only in spirit (see pic vent hose). My cab air vent was set to 'recirculate', meaning the switch had opened the vac feed to the power the actuator, and thus vented the whole vac system, disabling both the vent and turbo actuators. Thinking back, this lined up with what seemed like a sudden loss in AC effectiveness, which I sidelined as unrelated.

So, for anyone in future, with an 02-04 vintage van and a seemingly inexplicable turbo cutout - before you spend $300 on a slack mechanic, $200 on an Autel MD802 or $100 on a new solenoid: try just selecting fresh air feed to the cab, and then cycling the ignition and see what it does. If it fixes the problem, you have your answer.
 

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Midwestdrifter

Engineer In Residence
Its a strange thing that mercedes used a vacuum actuator on the recirculate damper. Must be a hold over from the earlier T1 or D series T1N? Strangely enough the vans don't throw a code or check engine light when they can't build boost? That's an oversight if I have ever seen one.
 

VanHausen

New member
Its a strange thing that mercedes used a vacuum actuator on the recirculate damper. Must be a hold over from the earlier T1 or D series T1N? Strangely enough the vans don't throw a code or check engine light when they can't build boost? That's an oversight if I have ever seen one.
Indeed.

I still don't know if the power loss is due to the ECU detecting something, and saying "shut down the turbo, somethings wrong..but not wrong enough to tell the driver" (as if we wouldn't notice the crippling power reduction?) OR if the ECU is still merrily telling the the solenoid to pump away, unaware that nothing's actually happening do to vac loss.

Surely the ECU is aware of the MAP reduction and makes some sort of compensation?
 

220629

Well-known member
Its a strange thing that mercedes used a vacuum actuator on the recirculate damper. Must be a hold over from the earlier T1 or D series T1N?
Maybe because vacuum actuators easily produce linear motion, are relatively inexpensive and generally reliable. The vacuum source is there for the power brakes it doesn't need to be added.

Strangely enough the vans don't throw a code or check engine light when they can't build boost? That's an oversight if I have ever seen one.
That has always irked me too. If the ECM aka ECU sets any LHM power reduction the operator should be informed. Keep in mind that not all LHM events kill the turbo. Some set a power (fuel rail pressure reduced) or RPM max limit.

:cheers: vic
 
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