308d van - those vacuum pipes!

[smokin]

hi all. ive recently aquired a 308d (transporter) based camper on a q plate - unknown year of manufacture but between 90 and 95 i believe. it runs sweet as a nut (not the fastest thing in the world though!) except for one niggle - restarting the engine. it starts fine after a long stop but not after just popping in the shops for example - if it does start sometimes it does so badly and shakes violently. After some snooping around the vehicle and the net i am now aware of the vacuum fuel cutoff employed by this van that runs through the ignition switch. There are three vacuum pipes coming through the bulkhead from the engine - 2 brown (with a stripe) and one black. the 2 brown go to the igintion switch (which is keyed different to the rest of the van) the black one goes nowhere! i have realised by sucking hard on this pipe whilst starting the van solves the problem - it goes back to the fuel pump diaphragm connected via a rubber y piece with a small clear valve(?) - looks like a non return valve as used in aquarium airlines.

so - where does this pipe go - do i have the wrong type of ignition switch (ie should have 3 connections for vacuum and not 2?) or does it go elsewhere? it looks like one of the brown pipes leads to the braking system near the master cylinder (i presume its the brakes - but what do i know i thought the fuel filter was the oil filter - first merc!)

hope some light can be shed on this prob

thanks in advance

chris

 

[smokin]

no one any idea then?

atb

chris

 

[Blobcat]

I expect that our van dring members are sleeping pending Monday morning. I'm sure one will be up soon to help you out.

 

[smokin]

just a nudge to the top for this please

atb

chris

 

[Sprint'n'Go]

I expect that our van dring members are sleeping pending Monday morning. I'm sure one will be up soon to help you out.

Hi Honey, I'm Home..............

Work finished, paperwork filed, family fed, pots washed, kids into bed...........

CDI sprinters do have the thin brown pipes but these do not go via the ignition as I presume these later engines are stopped electronically. However, my old 307D did use this system to stop the engine and logically it must work by applying a vacuum to the stop diaphragm to cut fuel supply hence the 2 pipes to the ignition switch. If it was just a case of breaking the vacuum to stop the engine then it would only need one pipe to the ignition but you would struggle like hell to restart as there would be no vacuum available until the engine was up and running again. Did you follow that? The vacuum is picked up from the brake servo system which in turn gets its vacuum from a mechanical vacuum pump as diesels do not get a negative air pressure in the inlet manifold unlike petrol engines.

My guess is that at some point in the past the ignition switch part of the system went faulty and the engine wouldn't stop so the additional black pipe was linked in to somehow get around the fault without fixing it. In my experience these vacuum pipes are only ever brown on Mercedes vans. I would first try to temporarily remove the black pipe and non return valve and blank the hole in the Y piece by plugging it with something suitable then see if that helps. The stop valve can go faulty but it then refuses to stop the engine, not cause problems starting. I don't see how sucking on the pipe helps unless my logic is wrong. You can safely experiment by unplugging various pipes while the engine is running to establish how it works. You won't do any harm, either the engine will stop or it won't. Just be careful not to catch your fingers in any moving engine parts!

If removing the surplus pipe work doesn't help then you could politely ask someone with a similar van if you can have a look at their plumbing, there is still loads of them about.

Let us know how you get on.

 

[smokin]

thanks for the reply mr sprint'n'go! - i forget you 'real' van drivers have work to do!! -

think i know where youre coming from - i did suspect the system worked the other way - ie you have to have vacuum applied to allow the fuel through (pulling it open) but im easy either way!!

i have tried blanking the pipe with no suck-sess if youll excuse the pun but i havent removed it totally as it does look like oe fitment. my local spanner monkey has had a look (and looked at a couple of merc vans at the local van scrappy a few doors away from my house) to no avail. ill try and post some piccies to see if that helps.

the grommet that the 3 pipes pass through the bulkhead does have 3 holes in it as thought it was meant to be there - thats why i thought the ignition switch could be wrong - plus the pipe is the right length for that as well - it currently is just free swinging under the dash. incidentally - if you suck on it when the engine is running the idle increases a hundred rpm or so.

as a slight aside - i did get the van running without it last week with a bit of right foot - but the bar steward died again at the next set of lights chalf a mile down the road - rather embarrasing!! - but it didnt run bad at all whilst on the go - was just like having no choke on a cold petrol engine

sucked on it again tonight after stopping at the shop on way home from work - it starts every time with a good suck (easy now!!) - searched the net to no gain however one site did say the black pipe is sometimes a vaccuum vent on some mercs (also said black pipe is sometimes a generic replacement for the coloured ones causing confusion later on!!)

as for there being plenty of 308s around - hmmm - see a few but not as many as id like to (loads in wales on hol in july/aug though esp anglesey)

hope i can sort it - im chuffed as hell with it otherwise- plus its given me a sense of 'take it easy maan!' on the road compared to my last vehichles (mugen import honda prelude and toyota surf) - i dont get so brassed off now when im smoked at the lights!!


once again - thanks for your input

atb

chris

ps i do have the mercedes wis cd's but i find them harder to use than the installation was - and thats saying something!! - is there a tutorial anywhere - i dont think im thick but it seems really antiquated to use - plus being on a q plate (and poss stolen recovered in the past) - i dont have the full vin info - just chassis number and some odd stampings in the doorways - i dont suspect anything dodgy and i trust the seller 99.9% - i know the vehicle was stood 4 years plus with front end damage and then purchased as a project by the seller hence the lack of 'passed on info' - if anyone can help me throught wis maybe i could find some answers!!!