Distributor Vacuum Advance

[billybluesky 1]

Hi, forgive my ignorance but after recently re-commisioning my 1.6 pug i gave it a once over and noticed that the vacuum pipe was off the adance and retard unit, after putting it back on the engine wouldn`t run, now ive had the car for about 12 years and i guess its never been on all this time, I presume the previous owner took it off and re timed the engine, the question is, is the vacuum unit a "belt and braces" job as other instalations with ecu`s run without vacuum a&r units, the ecu controls the spark. so is the vacuum relly necessary?

[Tom Fenton 1,542]

The vac advance increase the timing on part throttle. If it's not working or disconnected it will cost you mpg on cruise.

 

Check it hasn't been disconnected because the diaphragm is split (common). Attach a bit of pipe and suck. If no resistance then it's split inside.

[billybluesky 1]

One thing still baffleing me is why it wouldn`t start after re-conecting it, the engine just coughed and spat back when I stopped turning it over, would tha mean it was retarded? Then when I took the pipe back off it started as normal. Now since disturbing things iv`e got a missfire until it`s warmed up!

[hoodygoodwood 71 3 Cars]

Having the vacuum advance pipe on or off would not normally stop an engine starting . While you were working on the engine are you sure you have not disturbed a connection , most of the Bosch electrical connectors have a wire locking piece but these are often missing meaning it can work loose .Could the dizzy nuts be loose so it twisted when you pushed the pipe back on ?

[billybluesky 1]

No definately seemed to be spitting back and as soon as i disconnect the pipe starts first turn .tried it again ....same result, tested the diaphragm and it seems to be split, can these be repaired without a dizzy overhaul?

[erbs 42 1 Cars]

No definately seemed to be spitting back and as soon as i disconnect the pipe starts first turn .tried it again ....same result, tested the diaphragm and it seems to be split, can these be repaired without a dizzy overhaul?

Nope, need to be overhauled or find a replacement

[Tom Fenton 1,542]

Yes you can replace the vac advance unit without having to dismantle the rest of the dizzy.

[lagonda 42]

Bought a new (and correct Bosch numbered) vacuum advance unit for my CTi recently, here in France, for around €42. Easily replaced but you'll need to remove the distributor first. Just held on with a couple of screws, but engaging the connecting rod to the internal drive pin is tricky. Don't forget to mark distributor for timing before removing it.

Regarding the engine starting problem, if the vacuum pipe was not blanked off, it would be bleeding a small amount of unmetered air into the throttle body; your set up may have (inadvertently?) been tuned to cope with that. Reconnecting the pipe would stop that air bleed, but whether that would make enough difference to create starting difficulties I don't know...unlikely I'd have thought, but it's the only explanation I can think of. Even that doesn't totally explain it, as if your present diaphragm is split, air will still be sucked through, unless the distributor body and cap are completely airtight.