engine won't stop on 308d ,1994

schmiteysmith

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308d, 1994, 2.3ltr
After replacing the vacuum pump, master brake cylinder and brake servo, the engine still won't stop and I've still no brakes. How do I check the vacuum line.
What else could be wrong.
 

television

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2002 SL500, 216 CL500, all fully loaded
The engine stop is vacuum operated so a fault in the vacuum somewhere
 

WG M-B

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C63 Wagon in black
The gear that drives the vac pump is the fuel pump drive gear from memory
It has a kind of cam lobe on it. Is this the problem? Have you removed the main vac pipe from the pump and checked to see if the pump is creating a vacuum (being driven) ???
 

geezer255

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ESSEX!!
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Sprinter 311cdi - Shogun Sport
Does that year still have vac pipes that go to the headlights?
I once left them off after taking the front off and couldnt work out what the hell I had done cause it wouldnt turn off!
 

television

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2002 SL500, 216 CL500, all fully loaded
Yes it does have the same system for the light leveling.
 

wireman

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nice 201 2.5D 1993 & very nice 129 SL500 1994
Remove the servo vac pipe at the pump, run the engine and your finger should stick to the pump union if its working, a vacuum gauge would be a better test, expect about 25"Hg, -0.8bar minimum.

The headlamp levelling is fed via a restrictor from a second tapping on the pump, this should not affect the stop or servo operation if its leaking or faulty. On some models this vac is also used by the auto tranny and heater controls.

The engine stop vac is taken from a dedicated tapping on the servo pipe. the 190D & 250D have brown & brown/red 4mm nylon pipes on the stop system.

I have experienced a couple of failed 4mm pipes where they have hardened due to age and split along the pipe.

The servo assistance should available with major leaks on any of the extra vac equipment leaking or disconnected, so methinks you have a problem with the vacuum pump itself or a major leak inside the servo, listen for hissing around the pump and brake pedal when the engine is running.

The pump drive is off the fuel pump gear by an axial (in/out) cam operating on a roller lever which drives the pumps piston. A serious failure of this mechanism can result in strange tapping/knocking noises followed by bits falling into the moving timing chain with very unpleasant results.
 
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schmiteysmith

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308d, 1994, 2.3ltr
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  • #7
vacuum problems on 308d

Thanks for the info. I undid the airline to the servo and my finger stuck to it, so there was a vacuum. I put a rubber glove over the master cylinder hole on the servo, and it sucked it in (with the airline reconnected). THis resulted in me making a simple cardboard gasket, with grease on both sides, reassembling, and the engine now shuts off.:D
 


Mercedes-Benz Servicing, repairs, engine and diagnostics
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