Vacuum Leak and other problems

XJ
21

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Your ign advance is too high, Con - if checked at 900 rpms…

Depending on market; around 5 deg (European), and some 17 deg (US) - vacuum disconnected (at 800 rpms).

To verify which; check vacuum at dist hose. If manifold vacuum; European - if no vacuum US ‘ported’. After setting advance it is perfectly normal to tweak advance a bit, based on test driving.

900 rpms idle is fair enough - is that the limit with the idle screw?The cut-out in reverse may relate to too high advance, but also, combined with the high idle, may indicate a vacuum leak - from 900 idle should drop to some 750.

What is the drop if you turn AC on?

Frank
xj6 85 Sov Europe (UK/NZ)
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22

Or 10° static to begin with.
Mine idles at ~700 and is far from done in gear with the steering locked. It can go down to at least 250 rpm or so (if I forced it), and not die: the cut out could be a weak engine. If it dies with the screw turned 2 revolutions, and now it does not run anymore, turn it in fully and see if you can call it a day? That’s what I did.

David

23

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Not static setting is given, David - and 10 deg is higher than dynamic European setting.

But you are right; an engine should be able to drop to 250 rpms without stalling - though such low rpms stresses the bearings. In my case, engine cut out instantly when dropping below 500 rpms, it was caused by a faulty ignition amplifier…

Frank
xj6 85 Sov Europe (U/NZ)
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Hi Aristides
I guess it is guess work. I have based this on a post by another JL member. Here is his post:

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I don’t have the facility to test for emissions on setting up the idle mix and was hoping that this would get me in the ballpark. Maybe not.
Paul: yes I thought it seemed a bit high but if it is going to damage the engine I will be happy to lower it. This is what the manual has to say about the setting:
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so 4 degrees is what is needed. I cannot get the timing down that low. As I retard the timing it starts to stutter and then it just stops.
Frank: when you say Europen manifold vacuum do you mean that the hose from the distributor? Should it be connected to the manifold? My hose is connected to one of the spigots on the side of the throttle body which I think are ported vacuum. Should I move it to a manifold spigot? The idle speed will go down further but it’s starting to get a bit lumpy down there. The AC is not connected or working at present due to a massive slash in one of the hoses. I’ll worry about that later before the hot weather comes again.
Is it possible, given that I cannot get the timing down lower, that the leads may be not in the right place, maybe 1 position out?
Con

25

Maybe your crankshaft damper has moved and the scale is no longer accurate. The pulses should be 120 degrees apart. I don’t know much about the vacuum routing - there is the drain, one manifold port (just under #1 intake at the rear), one to the brake booster, one ported at the throttle body and one for the fuel pressure regulator. Try plugging all but the regulator and distributor and see what happens?

26

Correction. 6°, not 10.

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Thanks David. I am a little concerned that I can’t seem to turn the distributor back much further than it is at the moment giving around 26 degrees advance (this is with the vacuum line disconnected but there doesn’t seems to be much difference with it connected or not) which seems to cause the motor to idle slower and then it dies. It now idles at 800 and still dies when put into gear. I am thinking of turning the idle back up a bit so that I can at least move the car when required. I will check the position of the indicator in case it has had a knock but I don’t think it has. I will try and static time it. if I can get it around factory spec and still running I will be very happy.
Con

28

if I lift the idle speed will that help with getting the advance down to 4 degrees without cutting out? Do I need to clean the air distribution block?
Con

29

Don’t know the details of the 6 Cyl. engine ignition system, but this indicates an inoperative/stuck vacuum/centrifugal advance. Have you checked inside your distributor ?

First you have to find #1 TDC and make sure that the timing mark is correct and that your your crankshaft damper has not moved as David suggested. +20° discrepancy is a lot.
Then check your static timing and make sure the distributor is aligned correctly and that the spark plugs are connected at the correct sequence.

30

That’s an interesting thought Aristedes hadn’t thought of checking the distributor itself. Guess my weekend now has a plan. The car has Lucas Constant Energy Ignition (CEI) no points but there is still vacuum advance so if it is stuck on full that could put the timing out? How does one turn the motor for static testing the timing? If I remove all the plugs will that make it easier to turn it by hand?
Con

31

When the diaphragm in the vacuum advance brakes it just renders it inoperable.
Centrifugal advance can be stuck in any position. Must check both.
Kirby’s book has an extensive description on the the V12 distributor rebuild, the principles are the same.
You can turn the motor from the front belt pulley/damper, spark plugs out will indeed help greatly.
Turn only in the direction the engine turns as not to damage the cam chain tensioner.

32

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The point is whether that spigot delivers ‘manifold’ or ‘ported’ vacuum, Con - best checked at the distributor vacuum hose with the engine running…

The external location of a spigot doesn’t necessarily confirm the vacuum it delivers - just check to clarify. It’s a bewildering range of advance settings between model years/markets - but assuming you have an original Australian 85; the 4 deg is relevant. And it indeed implies that it should have ‘manifold’ vacuum at the dist vacuum hose…

The difficulties with positioning the dist for 4 deg advance may have various causes, but basically my be the choice of plug lead connections to the dist lid.

Turn the dist so the vacuum spigot points rearwards for nearest connection to the vacuum line. Set the engine to TDC mark and remove dist lid and note position of the rotor. Rotor must now point to the #6 (frontmost) or #1 (rearmost) plug lead. Hand trace the leads from lid to the relevant plug to make sure…

Nominally; the #6 lead is around 5 o’clock and the #1 at 11 o’clock, looking down at the dist. However, if the dist is put in at different positions; the position of the rotor will be stationary - but will point to different holes in the lid. As the #6 lead (reference cylinder) must(!) be placed in the hole pointed to by the rotor - the vacuum capsule (or whatever limits the travel of the dist for initial ign timing) may point ‘anywhere’…

Ie; verify what is limiting the counterclockwise turning of your dist. Then reposition the dist and visualize if moving all the leads one step on the lid - or move the leads on the lid. Then turn the dist to turn the dist to make the rotor to line up with the #6 lead.

In other words: While turning the dist the rotor direction remains fixed. But the rotor must point to plug lead of the cylinder ready to fire, which is #6 or #1 depending on which TDC the engine is set to)with the engine at TDC. And the initial position of the dist dictates the adjustment range of turning the dist for ign timing…phew…:slight_smile:

That said; you don’t mention if the engine is misfiring, which may indicate ‘crossed’ leads. But verifying ignition sequence is a good idea - particularly if the plug leads have been disconnected.

Having placed the #6 lead; place the next leads counterclockwise on the dist lid in the ign sequence 6-2-4-1-5-3. (Or, if the engine is set at ‘the other’ TDC; 1-5-3-6-2-4). In the process; hand trace each lead form the plug to the dist lead and bac - it’s incredibly easy to get lost…:slight_smile:

If all this does not solve the timing problem; David’s input about the pointer/scale on the damper being misaligned is relevant - in which case the advance cannot be reliably set. You absolutely need to check this; remove the #6 spark plug and turn the engine to bring the piston up to its highest point - using a rod, or whatever, to verify.

The piston is now at TDC - and the pointer at the dampers scale should read ‘0’. If not; the damper might indeed be adrift, which require replacement - or the pointer might be bent/displaced. The pointer/scale must be correct for any meaningful advance setting work! Do this before proceeding - the engine is indeed easier to turn with the spark plugs removed…:slight_smile:

As an aside; increasing idle will not(!) solve the timing problem…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
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Frank, do I need to verify the position of the cams if I bring the #6 piston (the closest to the front?) to the top of the cylinder?

34

No, if the rotor in the distributor points roughly at the cable for the frontmost piston, #6, then you’re good. For setting the timing you probably don’t need to do this, it will spark 360° out just as well - in that case you can look at the #1 plug for sparks. I just use the centre lead from the coil, a few millimetres from the block and voila, spark. Doesn’t matter which of the two cylinders it is, as long as you know it runs.

The spigot on the throttle is the only ported vacuum. Everything after is manifold!

David

35

Thank You David and Frank you are both your usual font of information. It’s a lot to digest . I will follow up once I have done so and checked out the timing. One thought I had is that maybe the vacuum advance mechanism has failed as Aristedes suggested and that is why the idle was so high not the work of the PO at all. Is that likely? Would that explain why,now that I have dropped the idle down to 800 the car just doesn’t want to move without dying?
Con

36

I don’t know, but you can try. Since you want to set the timing anyways, ideally pull the distributor out and see if both mechanical and vacuum advance work properly. Take pictures!

37

Con,
Just open your distributor and check everything.
The centrifugal advance should move freely and readily return to it’s initial position.
You can check the vacuum advance by applying vacuum directly with a big syringe or power-vac.
Then follow Frank and David’s procedure to establish a ballpark static timing.
Nevertheless, you have to be sure that your TDC mark is indeed correct. A very accurate way is to mesure with a rod, as Frank described, but take two equal measurements, one slightly before TDC and one after. Mark the two pints and in the middle it’s TDC.
The point is that at TDC there is some degrees of crank movement but hardly any at the piston.

38

Con,
Why wonder about the distributor vacuum advance? Test it and know. With the engine not running remove the distributor cap, disconnect the hose to the distributor vacuum advance capsule, connect an inexpensive hand held vacuum tester to the vacuum advance capsule nipple and pump away. If your vacuum advance is working you will see vacuum being held on the gauge and rotation in the distributor. If the vacuum advance has failed you will not hold any vacuum and there will be not be any rotation.
This is how I discovered a failed vacuum advance in my 1990 V12 Vanden Plas last year. It is a different distributor but the same principle applies. BTW, I believe that some slow bleed off of vacuum is designed into the capsules, at least it is on the V12 distributors. The bleed off of vacuum should not be instantaneous but it should bleed off slowly.

Paul

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You can even wrap the hose with some tape and suck, it will do.

40

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With engine set to TDC, Con; both the #1 and #6 piston is at their TDC. But only one is at the firing stroke - and the rotor must point to the correct one. As your engine is actually running you are in the ballpark - and the rotor position is a relevant verification of the appropriate TDC. Easier than using the cams as verification…:slight_smile:

Turn the dist to a position that gives best adjustment freedom either way. Check rotor position and turn the dist slightly to align the rotor to the nearest tab inside the dist lid - and note which one; this is your reference. Tighten the dist clamp slightly to prevent accidental movement.

Check that the plug lead at the reference is either #1 or #6 - one is close to the reference, the other one 180 degrees off. The close one is your reference cylinder. Remove plug leads.

Trace plug lead from the reference cylinder and place it in the reference hole in the dist lid. Trace each plug lead in turn from plug to dist and place leads counterclockwise from the reference in ignition sequence. If #1; 1-5-3-6-2-4. if #6; 6-2-4-1-5-3. Recheck to verify.

You may prefer, if the rotor is not pointing roughly in the direction of the #6 plug lead, to turn the engine one full revolution - again setting engine to TDC. The rest of the procedure is as described.

You can now either set ign timing static or, better, dymamic to relevant advance.

The problem was likely that proper procedure was not followed - leading to wrong timing and lack of adjustment space for the dist…

If engine does not perform properly with spec advance; you need to check the pointer/scale at the damper…

Frank
xj6 85 Sov Europe (UK/NZ)
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