V8 Distributor Vacuum advance not working.

Hi, I have a 3.9 EFI Discovery 1.

After some advice I took off my dizzy cap and disconnected the Vacuum pipe from the inlet manifold and sucked on it.

I did not see any movement in the Dizzy as I was told I should.

The rotar arm has some movement by hand but nothing by the vacuum.

The bit on the side of the Dizzy where the pipe fits has another pipe connection, but this has been blanked off. In fact someone has screwed a self tapper in the end and it has broken off

Would this cause my poor power and thirsty engine?

What can I do to fix it or do I need to replace the whole Dizzy?

The bit on the side has a little movement, its not firmly fixed if that helps.

Cheers

Brian

I would look elsewhere for a lack of power,failing oxygen sensors or vacuum leaks are the usual suspects.(Assuming you already have done Leads/cap/rotor and plugs -NGK and genuine for the rest.)

The vacuum device you speak of is a more of a RETARD mechanism.

At LOW manifold pressures (foot to the floor on the go pedal) the timing is RETARDED to stop pinking (detonation) which can wreck pistons and rings. When you have LESS throttle the engine can stand more advance.

If you have timed the engine properly, the right way will say whether you should have the vacuum pipe OFF or ON. It could be either, but it will be the one or the other, and it might make a BIG difference. Basically you need to get it working soon.

One thing for sure - the way the factory suggests you time the engine is more than likely quite a good way to do it. But vacuum pipe ON or OFF ?????

CharlesY

You should time your engine with the vac off .
Soon as you connect it again the ign will be instantly advanced via the engine vacuum on tickover and the revs will rise due to the fact that the engine is running more efficiently because the revs are low and there is no throttle to speak of and it is now getting the advance it needs to burn the fuel propper.
If you then shove your boot to the floor the ign will retard to the setting you set it at with the vac pipe off and will only advance if you lift your foot. This advance is to compensate for the weak fuel mixture that the engine is now getting and can be as much as 40/50 degrees advance at a light throttle cruising situation.
So the engine should have as much advance as poss without it pinking under load, sod what the manufacturers say, get the timing right and the engine will fly.
Most race engines take the vac advance off, now this is only a safety measure to protect the engine should the advance mechanism break , throwing the timing way out during a race and wrecking the engine. Most unlikely but you never know so they leave it off. Not a good move really beacause an engine with a race cam in it needs about 25 degrees or more of advance to tickover smoothly, thats why they sound lumpy in the pits, it dosent have to be like that, you can tune/alter the dizzy to run nicely at all revs if you know what you are doing.

Dont know what the retard pipe is all about on a V8 though or how it opperates so can someone enlighten me.

Thanks for the replies guys, These are things I did not know.

Now I understand what it does and I have tested mine to see it is not working what do I do?

Is this attachment replaceable?

What symptoms should I get from it not working?

From reading it a few times it does make a bit of sense to me.

If I drive my Landy carefully to preserve the fuel then it seems un naturally sluggish, like I'm driving a 500cc gutless fiat or something with about 50 BHP, but if I put my foot down harder on the pedal it goes ok ish, and only realy feels ok when the Pedal is buried in the carpet and the kickdown comes in.

If the vacuum advance/retard is not working properly you are likely to have the engine stalling on over-run and pick up off the line may not be what it shoud be. Replacement is easy, so get a new vacuum unit and stick it on at the same time, take the plenum off and give it a clean - trust me it is worth it. If there are significant running issues ther are many things you will need to check but a quick search shoiuld see you right, either search the whole LZ forum or jump between Disco and Range Rover.

Brian S said:

Thanks for the replies guys, These are things I did not know.

Now I understand what it does and I have tested mine to see it is not working what do I do?

Is this attachment replaceable?

What symptoms should I get from it not working?

From reading it a few times it does make a bit of sense to me.

If I drive my Landy carefully to preserve the fuel then it seems un naturally sluggish, like I'm driving a 500cc gutless fiat or something with about 50 BHP, but if I put my foot down harder on the pedal it goes ok ish, and only realy feels ok when the Pedal is buried in the carpet and the kickdown comes in.

Click to expand...

It should go Ok even on a light throttle, symptoms from the vac advance not working would be as you have stated. Check that the pipe from the engine is Ok. With the engine ticking over , remove the vac pipe, the engine should slow down .
The vac advance system is replaceable on the older non elctronic type dizzys but not sure on the new type.
Best thing is to replace with a known good one if you can or test the advance with a timing light, this will show if it is working propperly.
The engine should fly on half throttle and respond to the lightest touch on the pedal if everything is Ok with timing and fueling.

The weaker the fuel/air mix the more advance the engine requires and the vac advance does this as there is more vacuum with the throttle shut or part open.
Full throttle and there is no extra advance as there is little vacuum from the engine as the thottle is wide open max fueling), so the timing is as set at static, that is when the engine is stationary and the timing set to the timing marks on the pulley.
Am I making sense

Perfect sense, Cheers.

There is a vacuum on idle as I checked this wth my thumb over the pipe

I went to Graytec in Braintree today and booked it into them for a diagnostic check and timing check.

Hopefully they can sort it all out and I can get the divability I wanted by choosing a V8.

My mates got a 200 Diesel on large mud tyres and 2" lift and he goes faster than me on the road.

Another friend has a 300 Diesel engine with Auto box in his 90 and even he is faster than mine on even bigger mud tyres and 2" lift.

Brian S said:

Perfect sense, Cheers.

There is a vacuum on idle as I checked this wth my thumb over the pipe

I went to Graytec in Braintree today and booked it into them for a diagnostic check and timing check.

Hopefully they can sort it all out and I can get the divability I wanted by choosing a V8.

My mates got a 200 Diesel on large mud tyres and 2" lift and he goes faster than me on the road.

Another friend has a 300 Diesel engine with Auto box in his 90 and even he is faster than mine on even bigger mud tyres and 2" lift.

Click to expand...

V8 should rule

There is of course the mechanical advance via bobweights in the dizzy but that is even more info to digest. It adjusts timing to engine speed.

So how does one fit this vacuum advance thingymebob, does the whole dissy assembly need to be removed? Mine has no resistance either way, can suck and blow through the pipe, the pipe itself is fine.