Hi all. Still working my way through getting my 1980 series 3 running properly I came across a small regulator/valve in the vacuum hose going to the dizzy. It looks different to what I can find online as its only 2 hose spigots. The ones I’m seeing on line as have 3 hose spigots. Does this look right or is it a dodgy thing. I can suck through it one way ( towards the dizzy) with some resistance but not backwards towards the manifold. Any help greatly appreciated. Peter
That looks like the vacuum check valve that goes in-line between the vacuum/intake and brake booster. It will allow airflow on-way only, as you have confirmed. It does not belong in the dizzy system. My car is an '85 XJ6, and has a 3-port vacuum delay plastic fixture that goes in between the airflow meter and the dizzy. One port goes to intake vacuum, the other goes to the line from the airflow meter, and the other goes out to the dizzy.
Thanks Kassaq. Yeah that is my thoughts as well. I think a dodgy job. I will sorce an original part and see how that goes. Cheers Peter
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While I’m not fully familiar with the 1980 model year’s dizzy vacuum system, my 1985 system uses a ‘vacuum regulator’ in-line to the vacuum capsule on the dizzy. It serves to delay the full vacuum in the ignition advance when giving quick and heavy throttle. That way you (hopefully) don’t get quite so much pinging/pinking due to rapid advance of the timing under load.
Delay valves were usually associated with ‘ported’ vacuum, Peter and as Kassaq says; the three-way valve used to ‘blend’ manifold and ported sources. For some markets the ‘single’ input valve was used - so whether yours is relevant is uncertain - and may have failed as well. Delay was not used in ‘European’ markets with manifold vacuum…
Frank
xj6 85 Sov Europe (UK/NZ)
Thanks Doug. Thats a useful diagram. Looks as if that one way valve should be there but the 3 way one is missing. Does it need to be in the system or leave it out.
Doug I read the diag wrong. Any ideas where the one way valve heads
If your label is still under the hood, check the timing spec. If it is early enough to call for 4 Degrees BTDC, it uses regular ported vacuum. The one way valve is for the Ventilation system. The 3 way valve did not come into play until Jaguar specified 14, 16 and 17 Degrees BTDC.
Thanks Dick I will check that out. Peter
Wouldn’t that mean manifold vacuum, Dick…
Frank
xj6 85 Sov Europe (UK/NZ)
It’s indeed the check valve in your photo (C43639 in the diagram).
It splits with a T and one side goes to the vacuum tank (RH side engine compartment by the firewall) and the other to the climate control.
It’s purpose is to give some vacuum reserve for the climate control when in full throttle or when the engine is off.
The brake booster check valve that Kassaq referred to, is bigger and with a larger hose.
Thanks Aristides. this valve was in the vacuum hose to the distributor
And completely negate the vacuum advance…
Yes that’s what I thought. Seems a botch up to me
US market used ported vacuum only on the early XJ6 as mentioned. European cars used regular manifold vacuum.
Hi Dick. I’m in australia but I think that will apply to mine. The label under the bonnet is missing but the hadbook states 4deg advance. I’ll remove the small valve, as it wasn’t allowing vacuum to the dizzy and hook it up to manifold vacuum and see how that goes. Cheers Peter
The small one way (a large may be there for the brakes or incorporated into the manifold) should be so positioned that the manifold can suck air OUT of the vacuum system (climate control, that is including the reservac tank behind the brake booster). In other words you have to be able to blow air through towards the manifold.
Thanks David. The small one in the dizzy vacuum hose was allowing flow towards the dizzy therefore not allowing the vacuum to work the dizzy which in my reckoning wouldn’t do anything. Cheers Peter
[quote=“Aristides, post:12, topic:438332, full:true”
…It splits with a T and one side goes to the vacuum tank (RH side engine compartment by the firewall) and the other to the climate control.
It’s purpose is to give some vacuum reserve for the climate control when in full throttle or when the engine is off.
[/quote]
To amplify, Aristides; the vacuum tank retains the highest manifold vacuum in the manifold - on overrun it may reach 23" Hg. From the check valve a hose goes to a ‘T’ - one branch connects to the reservoir, the other through the firewall the AC system - hoses easily traced from the reservoir…
The AC only ‘uses up’ vacuum when resetting flaps etc - otherwise it is sealed, unless there is a leak. So the check valve ensures stable vacuum to the AC even when manifold vacuum varies with loads and pedal changes…
He should actually verify if the check valve is present and correct in the correct hose - ensuring against a possible misplacement of the AC check valve…?
Frank
xj6 85 Sov Europe (UK/NZ)