Vacuum Advancer

[Matt@TheBend]

Does anyone have any tips RE how to open and and test/recondition the vacuum advancer on a bosch distributer? Ive noticed in my 350se that the car is slower to pick up speed through to 90km/h than it should be, and i have a suspicion it could have soemthing to do with the advance/retard of the spark. Also, from looking at the plugs i notice some black buildup and am wondering if this could be a timing issue (fuel running rich).

The vac advancer looks like a sealed unit, but im having a hell of a time trying to ge hold of a new one, so any novel tips would be greatly appreciated!

thanks all,

matt 

[Nutz]

Remove the yellow/purple and red/purple vacuum lines from the distributor.Engine speed should increase slightly and then connect the yellow/purple line to the upper section of the vacuum diaphragm and the engine speed should increase more.If this doesn't happen,replace the 2 way vacuum diaphragm.

Just a kind suggestion,you should add which year and model W116 you have in your sig area and your location in your profile .

[s class]

Matt,

I agree with Nutz' suggestions, but from experience with M116 and M117 V8's I have often found that if disconnecting the vacuum leads to the distributor makes no differrence to the timing, a faulty diapragm is not the only possible culprit. 

On my 450 I found a number of vacuum leaks in the junctions of the pipes.  Trace the pipes from the vacuum advance diaphragm, especially the one that leads under the inlet manifold to the throttle body.  There are some black rubber "joiner" pieces that are often perished.  Sometimes you need to remove them and inspect them closely to find leaks. 

Given the cost of a vacuum advance diaphragm, I would first make sure there are no leaks in the pipes leading to it before replacing it.

I'm surprised you can't get one through the agents - you might also try sourcing it directly from the Bosch agents who in South Africa are Diesel Electric - they have branches in most major centres. 

Other suggestions - try www.autohauzaz.com - I have bought from them and found the service excellent.  They are an american site catering for the US market, so they don't list a 350SE, but it is quite possible that the 350SE vacuum unit would be the same as the 450SE unit of the same model year.  Just verify the Bosch numbers first. 

Ryan

[Matt@TheBend]

Thanks Nutz and Ryan, i pressure checked all pipes and 'joiners' and looks like the vac advance is dead, but only the advance diaphram. Im guessing its a stock part so i think its highly likely one of the membranes is punctured.

Ryan, thanks for your advice regarding Bosch in SA! i managed to get hold of someone who is looking into getting a new part for me, a major surprize considering its a saturday. my aim is to get the car ready for its first raodtrip under new ownership, and itll have to be Kruger.

matt
Nottingham Road, KZN

[oscar]

I just found my unit U/S as well

Doesn't surprise me.  I took my distributor out today to give it a real clean unlike my previous attempt.  Sucking on the outside connection of the Vac advance unit revealed no resistance.  I didn't bother checking the other, as that made my day right there,,, sort of,,, see the photos below of the pigtail to the trigger points disintergrated.  So that made my day too. 

The whole lot's been cleaned now, there's new points for the igniton and the trigger points look good.  Just a relube here and there and the lot will go back in.  The plastic around the terminals of the pigtail has been reformed from plastibond.  There'll be another pic tomorrow of the finished job.

But what to do about the cactus vacuum advance.  It's been U/S ever since I've had the car I suspect.  The way Matt talks about the loss in power reminds me of how my 350 used to be able to lose grip from a standing start 15yrs ago.  Anyone got a spare Vac advance unit?

[Bandolero]

A dead Vac Advance won't cause you to lack power at wide open throttle.
Vac advance only comes into play on part throttle to make the "drivability" of the car better.
Basically, it stops any hesitation at part throttle.
You could check the mechanical advance by lifting off the dist cap and push the rotor clockwise, then let go and see if it springs back nicely.

I bought a car once that had no power and I found the mechanical advance had seized up. I changed distributors and had "instant grunt!"

PS: If the vac advance leaks air (normal with a dead vac advance) you will have a vaccum leak, so you will have to plug the vac line(s).

[s class]

Bandolero,

I agree with what you say about the theory of vacuum advancement for full and part throttle, but the way I understand it is that if a car is tuned up and its static timing set correctly with a correctly functioning vacuum advance unit, all is well until the vacuum advance fails.  If no other tuning adjustments are made, the engine will be running with less spark advance at higher engines speeds than before, with a resultant loss of power.  Precisely what happened to my R107 450SL.  It now has a lot more grunt too (though it wold be even better with a new chain)

Ryan

[oscar]

Thanks fellas,

By pure chance I think I've noticed the mechanical advance work whilst playing with the rotor cap.  But I'll check again tomorrow.

Having cleaned the trigger points and distributor and lubed the shaft/s, I'm wondering now whether I need to lube the baseplate anywhere because the lot is grease free apart from the shaft? 

I've just put new leads on, reinstalled the distributor, new belts, retimed, new points set the dwell at 30 degress and how do you think the car ran??

Exactly the bloody same as with crappy leads, old points, old belts, grimey distributor.  Maybe my injectors need cleaning.  I hate putting hours in for a sore back and no noticeable improvement in the car .  But I know deep down my 350 appreciates my efforts 

For now I'll do as you say bandolero and block the lines after I do a test drive with lines connected then plugged.  I doubt whether I'll notice a difference.  Ryan, I think every time my car has been timed by mechs and me the vac advance has been kaput.  Your scenario reminds me of the fact that regardless of vac connected or not, timing never changed.  I noticed this first a while back when I asked questions here about "advance" and "BTDC" etc.

[john skene]

I started using fuel injector cleaner in each tankfull of fuel about 12 months ago, and my 450 motor is just running smoother and smoother with more urge each time I drive it.

If you decide to try a proprietary fuel injector cleaner rather than taking the injectors out for cleaning, read all the information on the bottle/can and you will soon pick up that there are a number of different "classes" of cleaner available. Even if you have to pay a lot extra, make sure you pick a brand that has a wide dosage tolerance, plus check that it can be used each time you fill.
Some injector cleaners advise they should only be used at each 3rd or 5th tankfull, I avoid these as they may only be an exotic solvent mix that can dilute the oil on your cylinder bores and may also run down to dilute your engine oil as well. That's not good.