Engine vibrating after warm-start

[XJ4081]

Hi,

I have another issue with my XJ12: on cold-start everything is running fine and smooth, also when driving for longer time, but when I stop the engine for let's say 10 or 15 minutes and then restart it, it is vibrating very explicitly, idle rev is only about 600 RPM. It's probably not running on all cylinders, even sounds odd at the exhaust. But it accepts gas without problems, above 1000 RPM vibrations are hardly recognizable, but probably still not running on all cylinders. After some minutes of driving it becomes better, but I cannot exclude that maybe 1 or 2 cylinders are still missing.

I had it checked at my Jag specialist, but he could not find an issue, spark cables and plugs are ok. He assumes it's the fuel injectors, some of them may be clotted due to long non-use (if it is true what the seller told me, the car has not been moved for about 8 years). But I am not sure if this issue has existed from the beginning of my ownership, it definitely got evident after I had the issues with water in the fuel tank. Could it be that some injectors got damaged by the water? My specialist recommended to use injection system cleaner (as additive for the fuel), but that did not help. Any ideas or hints?

Thanks and best regards,
Oliver

[Starbuck]

Hi Oliver,

In an earlier reply to you I suggested replacing all primary ignition components (plugs, leads, distributor cap, distributor rotor, coils, igniter modules) as a precautionary measure. The under bonnet ignition wiring loom should also be carefully checked.

It is not enough on these V12s that the spark plugs and leads look okay - the entire ignition system needs to be kept 'as new'. Failure to do this on the V12 can result in a very nasty vehicle fire if one bank of cylinders intermittently misfires or shuts down completely.

https://forums.jag-lovers.com/t/v12-eng ... res/134985

Best,

Starbuck

[XJ4081]

Hi Starbuck,

the very first time I was there I gave my specialist the order to check and replace all necessary ignition parts, but he said everything is fine, no replacement necessary. So it's a bit difficult to get this done if you are not one of the DIY guys - I could only try it with giving him the order 'Don't check, simply replace all ignition parts' . But I don't know in what this would result (unless I stood behind him and watch his fingers). I could try do it myself, but the result could be even worse .

Furthermore, if I got you right, you don't believe it could be related to the injectors?

Best regards
Oliver

[Starbuck]

Hi Oliver,

The ignition system on the V12 is one of those areas where, unfortunately, if you are not doing the work yourself you may have to demand that everything be replaced. A good Jaguar specialist will know about the Marelli ignition system and know that keeping everything 'as new' is very important.

You should be able to remove the centre cover off the engine yourself by undoing the four 'screws' - they just rotate through 90 degrees - just be careful not to lose them as they are spring loaded! Once the cover is off it is relatively easy to check what looks new and what doesn't and to make sure the work has been done.

An injector that is blocked or restricted is going to cause problems cold or hot, an injector with leak-down (i.e. it doesn't shut off properly), will cause black smoke at idle - and on the V12s an injector or two with leak-down can cause a lot of black smoke. Fuel injector cleaner is only really of any use on a car without blocked injectors, as it relies on flowing the cleaner through the injectors to work properly.

If the fuel injector cleaner didn't work your mechanic should have suggested that the injectors be removed, serviced, then replaced. Not a huge job on the V12 as they are relatively easily removed (one of the few things that are!). When they are cleaned and serviced they should come back with a report that tells you what their spray pattern and flow rate is. It isn't a cheap job though, as there are 12 of them.

If the car has been sitting for a long time it isn't going to hurt to have the injectors cleaned and serviced, just make sure your mechanic replaces the 'pintle caps' (little green plastic caps) on the nozzle of the injectors - a lot of places that clean and service injectors will supply the new caps.

A wide-band exhaust gas analyser (which any good mechanic should have) will also provide clues about what is going on. Your mechanic should know how to use one and what to look for if there is a fuel problem.

To me it sounds more like you have an ignition problem than a fuel problem. Although very rare on the V12, either the crank angle or crankshaft speed sensor could also have an intermittent fault but about the only way to analyse that is to replace them with known good units and see if it makes any difference.

Good hunting,

Starbuck

[newyankee]

I have the exact same issues. Low rpm idle at warm engine. And that odd vibration below 1000 rpm, feeling like a constant subtle misfire. It's none of that. They all do that, believe it or not (read posts on jag-lovers by steve). I carried out all of the suggested "repairs". Spark plugs, cables, rotor, cap, coils, amplifiers. Replaced fuel filter. Cleaned fuel system, cleaned injectors with ultrasound, fuel pressure regulator, timing re-adjusted, new timing chain and tensioner (unrelated). Adjusted valve clearances (royal PITA!) and put on new valve shaft seals. New lambda sensors. And more, forgot what else...

Result: 0, zero, naught, nothing.

Fuel consumption: 15.9l/100km min (perfect)
Emissions: Perfect (4-gas analyzer)
Power: As new (top speed 248 km/h)

Cure: Live with it.
Alternatives: Always drive car above 1000 rpm, never stop. Or buy a Lexus.

Guido

[ChrisW]

Worth checking is the state of the nitrile bushes on the linkage to each throttle body. They can fall apart with age and throw out the throttle synchronisation which causes a rough idle. In my case I think a previous owner had maladjusted the throttle stop on one bank to try and compensate for the missing nitrile bush. There is a good procedure for synchronising the throttles here:

http://www.jagrepair.com/images/TSB/TSB ... bility.pdf

If you look at page 30 of my V12 Rush thread there is a pic of the bush in situ.

viewtopic.php?f=33&t=6881&start=290

[Starbuck]

Hi Newyankee,

It's none of that. They all do that, believe it or not (read posts on jag-lovers by steve)

You are talking about lean misfire at idle, or at low revs with no load. To an extent they 'all do that', as Jaguar built lean burn into idle and low rpm off throttle to save fuel and provide quicker cat light up on ROW versions of the V12, but it shouldn't affect drivability under load and if it does there is something wrong. You didn't provide a link to 'Steve's' posts, but I'm guessing he eventually did some research and worked that out did he?

Both our '94 XJ12 and our Marelli ignition XJS have the barely perceptible lean misfire at idle and low revs off throttle, but it doesn't affect the drivability of either car and it is always there when hot, it doesn't go away then come back after you stop for 15 minutes. There is no vibration at idle on either of our cars - we can do the old party-trick of standing a coin on the engine at idle with no problems whatsoever. There should only be a barely audible (not felt) occasional 'pop' in the exhaust from lean misfire.

I take it in all the things you replaced, you did check that the outer half of the crankshaft damper with the timing star hadn't slipped relative to the centre hub? This is a very common fault on the V12s that throws the timing out. If you did you obviously did this with a degree wheel and dial indicator on number one piston to be 100% sure it hadn't slipped, as the V12s are very sensitive to this because of their very high compression ratio. It's amazing how many people miss that particular fault.

Oliver's car has been off the road for many years. Has had fuel pump issues, a broken petrol tank cap (so who knows how old the fuel was in the tank), water through the fuel system, voltage issues, and as yet we don't know what the state of the other components are on the ignition system. There have been a number of other posts about these issues too. As per Chris's comment, there are many other issues to potentially work through on Oliver's car. So in fact it could well be 'all of that', and more besides.

Best,

Starbuck

[newyankee]

You are talking about lean misfire at idle, or at low revs with no load. To an extent they 'all do that', as Jaguar built lean burn into idle and low rpm off throttle to save fuel and provide quicker cat light up on ROW versions of the V12, but it shouldn't affect drivability under load and if it does there is something wrong. You didn't provide a link to 'Steve's' posts, but I'm guessing he eventually did some research and worked that out did he?

Exactly. It doesn't affect drivability at all. No stumble on accel, but (constant) lean misfire at idle.

Posts on the old jag-lovers forum are a bit difficult to find, but these two links are a good starting point:
https://forums.jag-lovers.com/t/v12-engine-yet-again-idle-and-emissions-problems-with-a-6-0lv12/135062
https://forums.jag-lovers.com/t/v12-engine-engine-hp-torque-and-wide-band-o2-sensors-data-help-read/135070

... that the outer half of the crankshaft damper with the timing star hadn't slipped relative to the centre hub?

I don't think that this is possible on the XJ81 because of the design of how the timing star is attached to the centre part of the damper. While the outer part me be off, the star is firmly attached with screws in a single position determined by a roll pin.

[Starbuck]

Hi Newyankee,

Is that a photo of the pulley from your car, or taken off the Internet? On the 5.3s and 6.0s I have seen, the pointers are attached to the outer section of the pulley with three bolts and a roll pin, not to the pulley hub. Either that is a later supercession part (which wouldn't surprise me) or it is from another car.

For quite some time it was a very costly process to rectify the timing issue because very few places reconditioned them accurately enough when the outer pulley slipped, and I know of many being returned to be redone because they weren't indexed properly after reconditioning. It could be that Jaguar eventually got the message and altered the design. The pulleys also come loose on the crankshaft, chew the woodruff key, and upset the timing, but that is usually obvious because oil soon starts pouring out of the front seal.

From Oliver's description it sounds like the misfire is affecting the way the car drives. When that happens I am always suspicious the rotor insulation is starting to break down and the spark is earthing to ground via the distributor shaft. Our '94 car had plugs and leads every two years during its life, coils, every four or so, and one set of triggers (amplifiers) and the original rotor was only just starting to show signs of insulation break down at 120,000kms. The Marelli system can be very reliable when regularly serviced, the problem with Oliver's car is it seems to have been badly neglected for a while. For that reason I want to make absolutely sure there is no chance he could end up with a 'Marelli fire', as this is an unpleasant way to begin V12 ownership.

Best,

Starbuck

[newyankee]

The photo is off the internet, because I never took a photo of mine when I had it off. But this is how it looks on the 93-95 XJ81 6.0 litre.

I had mine off at least 4 times due to a leaking crank shaft front seal, poor quality replacement parts, broken timing chain tensioner and such. Not fun once the engine is back in the car...