XJ needs to be moved after 20 years... help please

XJ
1608

Max,

first thing I’d do is check the plugs’ color. Your city consumption sounds a bit high for a fuel injected car, unless this is really stop’n’go red lights city traffic. For suburban traffic it sounds way too high and reminds me of another fuel injected 6 cyl car I used that was tuned way too lean. Just a bit richer made its avg consumption drop from 15 to 11.5 litres, while highway consumption remained pretty much the same. And even if the plugs look ok, maybe you can get hold of an exhaust gas analyser.

As for the swaps: you can shortcut the HT wires thing with Frank’s test by a triple gapped extra plug. As for cap, rotor, coil, resistor it is an exercise of a Sat afternoon … provided, of course, you still get your hands on decent parts.

And yes, given the market value of series Jags you just found out why there are so few still around: the critical phase marked by market value depreciation and regain of market value for well-sorted specimen was too long given that the price of buying good services was too high.:frowning:

Even better though that you saved one wonderful car - great experience for you, great opportunity for your family and great entertainment for us (post # 1600;-)!

So, just keep going - you’ll eventually fix the last issues!

Jochen

75 XJ6L 4.2 auto (UK spec)

2 Likes
1609

How does this work?

1610

Less torque at lower RPM would make me do all the city traffic in second gear and even shift to second not before 2500 - the richer tuning allowed me to shift sooner and sometimes just use fourth even in lazy, but flowing city traffic.

Now, our cars are automatically shifted. Still you should feel when they do so. Is it very early? In regular suburban traffic I hardly see 2000 RPM and the gearbox will move quickly into third and do basically all the driving in third. How much pedal pressure do you need to accelerate? - The XK engine is a quite torquey engine and should deliver performance basically from 1200 RPM on on your big toe.

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

1611

Very subjectivity. Remember I have never driven another one but this one…

1612

Running too lean makes it run inefficient just as running too rich does. Maximum bang per amount of fuel per cycle gives maximum efficiency.

It is not excessively lean as the 0-100 is very much alright. But it may well be lean at idle.

1613

That’s my boy :smiley:

1 Like
1614

Ok so maybe it is running lean… here are the plugs close up. I feel like I am seeing a bit of something black on number 3 that the others don’t have.

Number 1

IMG_8868
IMG_88681920×2560 250 KB

Number 2

IMG_8867
IMG_88671920×2560 271 KB

Number 3

IMG_8866
IMG_88661920×2560 247 KB

Number 4

IMG_8864
IMG_88641920×2560 268 KB

Number 5

IMG_8863
IMG_88631920×2560 248 KB

Number 6

IMG_8860
IMG_88601920×2560 255 KB

1615

Yes it seems a bit lean.
But I don’t see any difference on #3…

2 Likes
1616

[quote=“XJFamilyJag, post:1614, topic:400182, full:true”]
Ok so maybe it is running lean… here are the plugs close up. I feel like I am seeing a bit of something black on number 3 that the others don’t have.
[unquote]

Considering you have been driving a lot at speed, Max; your plugs looks just right - and your petrol consumption is in the ball park. I don’t think you are running lean - but only a gas analyzer can properly tell…

It’s easier to observe fat running than lean by the plugs - the engine is set up to run fat in idle and when cold. At speed the xk usually shows its displeasure at lean running by hesitation and flat spots when accelerating…

Frank
xj6 85 Sov Europe (UK/NZ)

1617

Our problem is at idle and it is lean at idle

1618

Which would make it lean throughout, David - and should show up while driving. How is ‘lean’ confirmed? Short of a gas analyzer or may be ColorTune - a fractional prod on the AFM flap will enrich. If mixture is already ‘reasonable’ the engine will instantly react…?

If other methods to fatten the mixture has failed, including further closing of the AFM bypass screw - it may be the AFM itself needing adjustment? Ie, the range of the bypass is insufficient - and the AFM can be opened to adjust the flap spring. It’s of course factory set, but over time spring tension may relax - or a PO may have been in there.

Frank
xj6 85 Sov Europe (UK/NZ)

1619

If it’s another AFM/sensor issue.
You yourself always say that ‘the XK can run smoothly at higher speeds even if something is tremendously wrong’ and of course you are correct.
Leaks, the bypass screw, a slightly weak mixture, worn AFM tracks in the idle sector can all be masked or irrelevant at speed!
I did not mention the AFM spring but I know it would fatten the general mixture. It’s a last resort because the spring can’t change overnight.
It’s still possible that it is ignition or injector related. Maybe Max finds the time to do a little recap and list the issues that remain.

1620

I looked for a new Lucas coil but could not find out that was decently priced or not coming from the UK. I am currently really busy so I do not have much time to waste with customs officers during their superb opening hours so I ordered a direct replacement for a Lucas from Amazon. Honestly, I kind of like the red… But long story short It ran worse with the new coil than with my crusty Bosh unit from the parts car. I did measure them both and they are 12v and 3Ohm. I believe my original was a British layland uni-part with a ballast resistor. Unfortunately it was leaking liquid. Anyway that new unit is going back ASAP.

IMG_8883
IMG_88831920×2560 358 KB

1621

Do what others have said , Distributor Doctor !!!

1622

Nominally the xk CE would run equally well with ‘any’ coil, Max. But your ‘3 ohm’ is unusually high specified coils for the CE vary from 0,8 to 1,5 ohms…

Given that coils basically does the same thing - the manufacturers does reach that target in different ways. Both coils are marked ‘12V’…?

The high resistance may or may not play a part. Though it is harmless it may influence spark energy…?

Frank
xj6 85 Sov Europe (UK/NZ)

1623

Yes they are. And I was under the understanding that 12V 3ohm was normal when non ballasted. If ballast 6v 1.5ohm and that would equal the same thing under normal conditions except that the ballasted version has a bypass to use more when cranking thus theoretically increasing starting power… But I could be wrong.

1624

Your outline is not wrong, Max…

However, all coils for the xk is specified by primary coil resistance - ‘voltage rating’ is not mentioned. But all cars had of course 12V electrics.

Bewilderingly the obvious point distributors specified 1,2 - 1,5 ohms, no external resistor mentioned. Obvious CE coils specified 0,8 - 1 ohm (Ducellier) with a 1 ohm external resistor. However, as said; coil manufacturers use there own methods to reach required ignition voltages and energy. The voltage bridges the plug gap - it is the energy that ignites the petrol.

Part of the story is of course that few, if any, of the present cars run on the original coils. And omitting the ballast resistor (which occasionally causes trouble), has had no negative effects - and the xk runs happily on a variety of coils.

Electrically, max coil current is in any case limited by primary coil resistance - 3 ohm = 4A. While running, the current is further limited by coil impedance - which is the resistance of the coil to changing current. And of course, the average coil current reflects the ‘make and break’ in coil current - relating to the dwell angle.

One of the purposes of the points set-up’s external resistor was limiting coil current if the points was closed with the ign ‘on’, engine stationary - preventing coil burn-out/overheating. This is immaterial for electronic ignition - which is ‘break’ unless the engine is turning.

Adding to this, the AB14 amplifier is designed to control current flow to maintain C(onstant)E(nergy). Which means that the amplifier can reduce the coil current below the one related to coil primary resistance - but it cannot increase it beyond that.

Disregarding coil impedance (for crude comparison only!) your ‘3 ohms’ can deliver max 48W while ‘1,5 ohm’ can deliver max 96W. I’m certainly not saying that your high primary resistance is causing you problems - far from it. Only that the resistances specified in the manuals are half that - or less. For all I know; Jaguar used 6V coils…

The conclusion of all that is I don’t know what…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

1 Like
1625

I had 12v coils and they worked fine. Well. The first didn’t, the second didn’t, then I put a salvaged one in. That did.

12v means the coil is designed for a 12v system.

And 6v means the coil is designed for a 6v system.

A ballasted system imitates a 6v system and during cranking the coil gets ‚takeoff power‘.

The CEI should be able to do them all but since max removed his ballast a 12v coil seems to make sense.

1626

Well, David; the coil is just a transformer, changing battery voltages to ignition voltages - 5 KV or more…

Nothing disasterous happens instantly if a ‘6V’ coil is connected to 12V - and indeed; coils intended for 6V were used for 12V set-ups…

Crudely, if you double the number of primary coil windings you double the primary coils resistance - and halve the voltage output of the secondary windings. Or double the voltage applied to the same number of windings; you double the secondary voltage. Or double both the primary and secondary - you get the same secondary voltage. One point is that resistance crudely increases proportional to the length of a wire - and is inverse to the cross area…

This is principle of coils, and if the ‘switchgear’, points or electronic, can stand the higher voltage or current and the secondary voltage is high enough to spark the plugs, with enough energy the engine couldn’t care less…

So, in a way, the voltage rating of a coil is ‘advisory’, and its innards are left to the manufacturers - who certainly go deeper into construction than this.

My point was just that all the coils specified has an overall primary resistance of less than 1,5 ohms and the coil in question is 3 ohms. Which is of course ‘safer’, but less ‘energetic’ - which may be immaterial…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

3 Likes
1627

It’s been almost 4 weeks since the Jag moved. My daily is still broken with lots of oil in the coolant. At this point it also has a dead battery. Been really busy with school so no time to play with the jag and with the snow and slush I was forced to ride the bicycle everywhere. No big deal but cold as hell.

Today was sunny and I needed a break from the madness. No real reason to take the car out to go down the road to buy groceries.

Anyway for the sake of trial I gave the air intake a shot of break cleaner and then turned the key for the first time in almost 4 weeks. Engine was a live and well within 4 or 5 seconds. Usually it start a little rough on a few and then comes to life… Today once it caught it was there on all 6 immediately! So it is my believe my starting issues are just related to the missing CSI.

So down the road I went. All felt really nice. Clock working perfect. Drove by the car wash and sprayed her down with a bit of clean water and back to the garage. Good to know that the car still works. Just waiting for me. Also the smell of the interior after the long time in the garage is just amazing. To me it’s the nicest leather car smell in the world.

8 Likes