Thousand Dollar Supercar's 1988 Jaguar XJ-S 3.6

[Thousand Dollar Supercar]

Yay page 2! Discussion link: https://oldschool.co.nz/index.php?/topic/58671-thousand-dollar-supercars-1988-jaguar-xj-s-36/

The cheek of it - Dillon Photography cut me off in favour of some hairdresser's car! 

I filled the tank up with injector cleaner and went racing at Hampton Downs to blow out the cobwebs.

After I locked up my brakes severely and made huge clouds of smoke, the angry man driving the pace car informed me that we were not in fact racing - this was only the track cruise. 

[Thousand Dollar Supercar]

I went to visit some fuel injector specialists to see about eliminating possible causes of my car's stumbling idle and poor starting after days of inactivity. Because of the logistical hassles of leaving the car with them, I decided that I should first try ordering an injector seal kit myself.

Here's the fuel rail removed from the mighty AJ6. 'AJ' stands for 'Advanced Jaguar' - nothing but the finest electronic port fuel injection, don't you know.

I ripped into installing the pieces from the kit, having never dealt with fuel injectors before. I almost wrecked the first one trying to get the filter out of it - they're a tight press fit into the rail end of the injector.

Then I almost wrecked it again trying to get the old pintle cap off - they clip on firmly but the plastic was too old for my bodgy removal methods. Subsequent injectors got easier as I refined my methods, and eventually they were all done:

On the plus side, no injectors were harmed in the making of this post and the car still works. Unfortunately the idle's still not what I'd expect for an EFI car.

[Thousand Dollar Supercar]

So you're probably wondering why I haven't updated this thread in 1.5 years.

It's because the Jaguar bit me. 

 

 

I was driving home in about November 2020 and the engine was up to temp, so I decided to go for an onramp pull. It wasn't raining, I had new rear tyres, not much power, and I was only flooring it in a straight line, so nothing would go wrong.

Unfortunately the road was still a bit wet, the onramp was downhill and quite narrow. For a few seconds I was accelerating with full traction, still well short of the speed limit, then maybe the auto shifted gear or I hit some water or hit VTEC, and the rear stepped out to the right. I tried to catch it with the steering but I think I lifted completely off the throttle (I'm not experienced with RWD), and the car snapped back the other way. The back left corner of the car hit the concrete wall on the left side of the onramp, sending the car across into the barrier on the right. I hit that barrier squarely with the entire right side of the car. My side curtain airbags failed to deploy in the barrier impact, so my head whacked the driver's door window (cabin is pretty small). I managed to stop the car rebounding into anything else and I drove it home.

I could not sleep at all for the entire night. 

I kept imagining the police were watching their highway cameras and they'd turn up at my door to arrest me for toxic masculinity. I was very annoyed at myself for crashing another classic car (even one with unfriendly handling).

Now what? I had no insurance, and the car might be uneconomical to repair privately, particularly if I'd done any mechanical damage when the RF and RR wheels hit the barrier. So I took it to get the wheel alignment checked, and apparently it was all fine. Jolly solid car / that's why it's so heavy.

I parked the car up and started looking for parts. For the longest time, nobody was wrecking an XJS except the absolute worst of TradeMe sellers. I'm talking guys so lazy that actually buying anything off them is like solving a puzzle.  I had been starting the Jag every few months and moving it back and forward, but still the tyres got square and the leather got mouldy and the car got dusty etc.  I was tempted to abandon it and buy a more modern vehicle, but I eventually managed to get the bare minimum of B-grade parts to allow me to take the Jag to a panelbeater. I was worried that if I didn't get it back on the road in a somewhat timely manner, it would start to rust and degrade mechanically. The plan was to get it WOFable rather than presentable, so I could resume driving it.

(continued)

Edited June 12, 2022 by Thousand Dollar Supercar
fixing the images

[Thousand Dollar Supercar]

So I ended up spending almost what I paid for the car to get it mostly straight again. Justifications:

• I didn't want to be responsible for its death
• 'Better the devil you know / The best of the worst you can handle...'
• I need a car to take to Nats 2023
• Some of the cost was covered by all the money I saved by not putting petrol in the Jag for 1.5 years
• Also, you know, I wanted to contribute to the local economy after the covid downturn. 

I got it back in May 2022. The panelbeaters fixed it the old fashioned way without replacing panels / using rust repair sections etc. It's better and worse than before - I got a few rust bubbles and dents seen to, both sides of the car were repainted, the new paint is nice but was mixed to the paint code rather than matched to the other panels, the replacement lights and bumper bits are crappy. The car no longer has this pinstripe:

(I just thought the post needed a photo and I didn't take any)

I got busy refitting bits of trim and fixing stuff for a WOF, and happily the car only failed on an intermittent park light bulb (WOF inspector wasn't satisfied when I demonstrated how to make it work by hitting it like The Fonz).

So the Jag is back!

I filled it up with some fresh fuel, which cost about a dollar per litre more than the last time the car was on the road. 

On the day it passed its WOF, I took it to a gig in Morrinsville, which was over 200km of open road driving. The trip computer said 10.1 l/100km for the weekend, but more importantly the tyre vibrations and engine idle quality improved back to their baseline crappiness. I was reminded that the Jag feels a bit disconcerting at speed - the rear end wants to make you swerve like a drunken snake, so you have to keep a grip on the wheel and just use small steering inputs. Here's Jaguar test driver Norman Dewis explaining the very British reason the XJ-S has a rear rollbar despite it making the handling worse.  But I have missed these things:

• The instant response of a cable throttle and a naturally-aspirated engine (I daily a modern turbodiesel)
• The Jag's cartoonish decadence, absurd priorities and whimsical design
• Old car smell
• The motorboat-meets-line-trimmer noises it makes

Now I need to get it serviced and get back to all the tasks I put on hold.

Tell me how stupid I am: 

 

[Thousand Dollar Supercar]

This year I successfully got the Jag to New Plymboes, its first proper Oldschool meet:

It went fine the whole way there, fine all weekend, fine half of the way back...

Then I overtook grandpa's Yaris and one of the Jag's cooling system hoses decided to explode in the middle of the overtake. Fortunately the Jag has a coolant level warning indicator for just such occasions, and I was able to coast the short distance to Otorohanga. 

The hose which blew was a big one that runs from the back of the water pump along the side of the engine block. The failed hose wasn't an original part, suggesting this is a high-stress area of the cooling system? Anyway, the failure was on a long weekend but I still got into Mitre 10 for some repair tape ten minutes after their closing time. I thought I was saved. It turned out that the blown piece of hose was too close to the block for me to tape it up in situ, so it needed to come out. The hose was a mission to remove (which I did with the tools from my boot, in the parking lot of a petrol station), and it needed to be bent to get it out and back in again. This must have meant that my tape repair was weakened by the time I wrestled the hose back into place. It only held water until I was a minute or two out of town. 

I waited a bit long before pulling over, then I filled up the system with the water I'd brought with me and started heading back to Otorohanga. I tried to come up with what I hoped would be the kindest strategy for the engine - cruise at best economy rpm but fast enough for the injectors to shut off when coasting; switch the engine off down hills, stop once or twice to allow the engine to cool a bit...

I booked myself into a motel and booked a day off work. While the engine cooled, I turned it over on a few occasions for good luck. Next morning I went to see the local garage. Of course nobody in town has a hose large enough for the Jag.... 

Oldschool reminded me that @The Dudelives in Otorohanga.  I met up with him and he took me around every likely shop then out to Repco in the next town. A hose for a Holden Statesman was obtained, and I cut and fitted it back at the local garage. I think the garage were happy to let me do it myself, because the hose location was not very accessible and it took me ages to get the new piece to seal.

I got back to Auckland OK, and ever since then, I've been a bit nervous that SOMETHING must have been damaged. Can I really get away with overheating a British alloy straight six and not blow a head gasket / warp the block / soften the alloy / spin the bearings or something? If so, should I replace anything as a precaution? Answers on a postcard.

On with the impossible quest to make a Jag into a good car, I guess.

I pulled the windscreen wiper switch out again to have a proper go at fixing it. XJ-S wipers don't like to park, and this switch is one of the reasons why. The Barry Bible says that step 1 is to drill out the four rivets which hold the switch  together:

At this point, the switch comes apart and all the bits inside fly out before you get to see how they were fitting together.

Inside the switch there is this board with pieces of copper glued onto it:

The board moves up and down against pins in the switch as you move the wiper stalk. Usually what happens is that the copper pieces come unstuck from the board and just float around inside the switch, so you just have to glue them back on.

I did that, and reassembled everything before testing it. The problem was not fixed.

I think that my switch was also too worn, and this wear meant that the parking connection wasn't being made. In the photos below, the rotating arm should be pushing the sliding circuit board up far enough to make contact with the parking circuit:

I think the reason that's not happening is due to crappy tolerances and/or wear on all the plastic, particularly here:

I corrected for this by cutting a random piece of metal to act as a shim:

I then cable-tied the switch back together - Barry would be proud. It works, even though it's too tight at the moment, like using a column-change gearshift rather than a wiper stalk. It'll loosen up. Or it'll break. 

Now that the wipers park, I can see how badly they park. They change direction mid wipe and do another wipe or so for good measure before figuring out where their stop point is. Why can't the Brits figure out wipers? Even the Italians can do it better despite having relatively no rain.

Also, whatever you do...

 

Those are structural screws. If you remove them...  

 

[Thousand Dollar Supercar]

If you have a carburetted car and you find yourself inadvertently inverted, 

..it's OK because your engine won't keep running - carbs rely on gravity. On the other hand, a fuel-injected Jaguar is so reliable that it would definitely keep running in such a situation. Jaguar therefore equipped the XJ-S with this:

I just tested it today. Pull up the knob and the car stalls. Yusss. 

The knob stays up and the car won't start. Oldschool anti-theft immobiliser. 

"I am going to poo on your car!"

 

[Thousand Dollar Supercar]

The Jag still hasn't dropped a valve seat after I overheated it, so I guess I got away with that little incident. 

I have been driving it around more often to try to find issues ahead of the epic quest to the South Island, and so I can spend my credits on various power-ups to help me on that journey. I got a transmission service, which did not help the auto's whining/scraping noise or the rough shifting in and out of 1st gear. The tech said there were no filings in the transmission drain pan, and I should expect this noise to gradually worsen rather than to result in a sudden failure.

Meanwhile the tingling sensation in the steering from 80kph had been getting worse. I ordered front wheel bearing kits and they sat on my desk for ages until the noise and vibration became a bit scary, at which point I forced myself to have a go at actually installing them.

This was the first time I've done front wheel bearings, and I don't have much in the way of proper tools. I used a piece of deckchair framing as a breaker bar extension, vice grips instead of a brake pad spreader, a claw hammer instead of a seal puller etc.

When I removed the first bolts which go through the steering arm and the brake caliper into the hub, two 'washers' fell out from somewhere unknown. This is relevant later. 

The bearings were pretty worn, which was encouraging. Unfortunately it started looking like this task was not straightforward:

• The front discs have pronounced lips on them (I got a warning last WOF), so I guess they need machining or replacing.
• I couldn't get the old bearing races out (they were too stubborn for the hammer-and-screwdriver method which I'd previously used on my Alfa's rear drums), so I just reused them. At least one of them is looking a bit dodgy.
• This (see photo):

Apparently the wheel bearings like to spin on the stub axles and wear grooves into the undersides, as seen here.  The XJ-S Barry Bible recommends getting new stub axles and loctiting the bearings onto them so this doesn't happen.

By this point I'd decided I was just doing a temporary fix and that I'd get someone else to do it properly later. I slapped the new bearings in and put it all back together. I put the random mystery washers under the bolt heads.

When I went to put the factory wheels back on and go for a test drive, I noticed one of the Linglong tyres had a rivet embedded in the shoulder. I pulled the rivet out of the tyre and aaaall the air escaped. 

I got out the factory spare tyre and discovered it was undersized (215/60 instead of 235/60), so I swapped all the aftermarket wheels back on instead. This produced motorway smoothness of perhaps 8/10 - a new record during my ownership! 

Unfortunately my bearing change had clearly thrown the wheel alignment out. It turns out that the random mystery washers were actually spacers for the steering arms, and that I'd put them back in the wrong spot causing toe out.  I reluctantly spent the time to jam them back in the right positions. Now it's good again.

So after a few days getting greasy, I achieved:

• uncovering problems I'm unable to deal with
• wasting my new bearings on a dodgy repair that won't last
• puncturing a Linglong tyre so I can't use the factory wheels
• wasting valuable time to get professional work done on the car before Nats

Fun and games. 

[Thousand Dollar Supercar]

My tyre situation was:

1. Factory wheels: 3 x sketchy 10-year-old Linglongs which would probably never wear out, 1 x unrepairable Linglong, 1 x unusable spare
2. Aftermarket wheels: 2 x good Potenza RE003s, 2 x cracking 10-year-old Potenza RE002s, no 5th wheel to use as a spare, rolling radius does not match factory wheels.

Swapping between sets of wheels confirmed that the car doesn't drive as well on the 1-inch-wider aftermarket wheels and their lower-profile tyres. I think these wheels are at least partly responsible for the car wanting to fight you and to swerve drunkenly at speed. Maybe their offset isn't right.

So I decided to go with the factory mags for Nats, and to get four new retro bogan tyres with raised white lettering for them. As mentioned previously, the only tyre choices in this size are of the harder-than-a-whore's-heart / real-men-smoke-Eagers variety. On the plus side, this gives me a viable spare tyre in the form of one of the Linglongs.

• +1 to motorway smoothness, now up to an unbelievable 9/10. 
• +1 to annoying the classic car snobs, because raised-white-lettering tyres on an XJ-S look like this:

The Gingerbeard Man is more photogenic than me, and his car's tidier, so just imagine the discount version of this photo. 

[Thousand Dollar Supercar]

^ Some shady character....

Nats '23 in the South Island was approaching. I sent the Jag to get the wheel bearing races changed and the front brakes seen to as well. Apparently the calipers were seizing, which might explain why I felt the brakes had been easy to lock and slightly slow to unlock. Now I have new discs and pads and rebuilt calipers. While the Jag was at the shop for this work, Auckland got flooded, but fortunately the Jag escaped.

I was running out of time till Nats but still had more 'grand touring' issues to address. The driver's wing mirror glass was still too wobbly despite my best attempts, so I gave up and screwed the mechanism from a modern Japanese car into the Jaguar wing mirror housing. Shhh.  

The mirror glass now protrudes slightly rather than being recessed, but it no longer shakes around. I'll have another shot at this problem at some point.

The passenger side windscreen washer jet was only producing a useless dribble. Upon investigation I noticed that the factory washer nozzles are heated to prevent them icing up! This doesn't matter if they're corroded and useless. I temporarily substituted the nozzle from a garden sprayer and it's far superior. 

I topped up the diff, and while under there, I noticed this rear subframe mount is starting to come apart (yellow arrows):

This is the left rear one of four mounts which hold the rear subframe to the chassis.  After Nats, I ordered a new set which have since arrived but I haven't fitted them yet.

I decided I needed to make some visible modification to the car for Nats, to make it appear that I'm a legit car guy and not a chequebook racer / Sunday driver. I figured I could have a go at the dashboard veneer - grind off the lacquer then put Danish oil on it, same as I did for the centre console.

Before:

Unfortunately the 'after' photos (not included) don't look so good. I was in too much of a hurry and I burned the veneer with the stripping disc, ground through it in spots and tried to hurry the drying process too much. So now my dash looks a bit funky.  I Reassembled it anyway and drove from Auckland to Marahau and back.

 

On the way down from the ferry to Marahau, I rambled to my poor passenger Johnnyfive that the XJS could have done without IRS, RWS, LSD, inboard rear discs etc.. Then my favourite part of Nats turned out to be racing back over the hill in the above photo, chasing Yoeddynz's Imp and a bunch of motorbikes and making good use of those technical features. I was glad for my new brakes that didn't lock or fade, new tyres that let go progressively, diff that allowed me to plant the boot mid corner, handling that often seemed to allow me to turn harder than the limit at the cost of having the rear break away.. On that last point, I kept imagining I had more oversteer in one direction than in the other, due to that rear subframe mount which was surely tearing itself further to bits..

I got back home with no exploded coolant hoses, no exploded diff from oil starvation, not even that much engine oil consumption. Fuel economy never got better than 10l/100km on the trip, and I discovered the car would stumble and misfire more after several hours of driving. Add that to the list along with a sagging headlining.

One more fun fact - I weighed my wheel/tyre combos, because who doesn't enjoy a bit of Dave Science(tm).

1. 'Performance' 17x7.5 wheel only: 11.1kg
   • plus 10.2kg 235/45R17 Bridgestone Potenza tyre: total 21.3kg
2. Jaguar OEM 15x6.5 wheel: 8.4kg
   • plus 12kg 235/60R15 Linglong tyre: total 20.4kg
   • plus 10.9kg 235/60R15 Nankang tyre: total 19.3kg

So I save 2kg per corner by reverting to the combo with the best road manners. 

[Thousand Dollar Supercar]

The headlining in the Jag started to sag badly, so I took the whole thing out.

The backing is made of Weetbix covered in crumbling foam, and it's impossible to reuse at this point. The previous owner of my car was an upholsterer and his repair didn't last, cos nothing will stick to this flimsy mess.

So now I have no headlining and no interior lights. You can get replacement headlinings which have the Weetbix backing shell replaced by fibreglass or something, but the shipping from the UK is crazy.

On the Jag's last WOF inspection, they gave me a warning that they didn't like my aftermarket driving lights coming on with my high beams. Having the lights work that way made sense to me, but whatever, I figured I'd change them around to run off the front fog light circuit to keep the WOF man happy. Although my car didn't come with front fog lights from factory, it still has the dedicated fuse for them, and the dedicated SPARE fuse for them , and the headlight switch still has positions to activate them. So I figured I could just find the fog light plugs behind the bumper and they would already be functional / already be live when the headlight switch was set to the correct position. Right?

Nope.

After an hour or two of poking around, I found this stuffed in behind the headlight switch:

It's an adapter for cars without fog lights, and its purpose is to stop the headlights from turning off when you turn the headlight switch to the fogs-only position. 

The adapter also prevents the fog light plugs from becoming live, because it breaks the connection to the fog light circuit. You know, that same circuit which is nevertheless fitted with a fuse and a spare fuse.  You can see that the fog light circuit is discontinued in the photos below.

So I just removed the adapter completely. Now my fog light circuit is live. 

The aftermarket driving lights in my car were conveniently run off a relay rather than directly off the high beam circuit. I added a switch to toggle that relay's coil supply between the high beam circuit and the fog light circuit, in case a different WOF man takes a different view of how my driving lights should work in future. The relay and switch are sitting inside of one of the headlight recesses:

So now I have a way to drive around with just my driving lights on during the day, like a plonker. 

Then I actually went for the WOF, and failed because of a split steering rack boot. I replaced it all by myself, because I am a totally legit home mechanic.

Currently on the Jag's to-do list:

• Find another solution for the headlining
• Get the auto looked at (I'm pretty sure it's slipping and getting worse, so I'm afraid to use full throttle now)
• Stop the drivers window sticking
• Fix the radio (some speaker wiring must be shorting somewhere, cos no sound comes out)
• Install the new rear subframe mounts
• Install the new rear trailing radius arm bushes

I'm becoming more of a Jag man as time goes on. Check out my Jaaag fragrance collection, which lives in the car:

"Jaguar: Ultimate Power" (a couple of sprays on the car makes it go faster), and of course the Smell of Success.  Apparently, success smells like creme brulee / vanilla / caramelised sugar, whereas the Jaguar fragrance ironically smells like lemons.  

 

Edited December 23, 2023 by Thousand Dollar Supercar

[Thousand Dollar Supercar]

On 17/12/2023 at 13:04, Thousand Dollar Supercar said:

Currently on the Jag's to-do list:

• Find another solution for the headlining
• Get the auto looked at (I'm pretty sure it's slipping and getting worse, so I'm afraid to use full throttle now)
• Stop the drivers window sticking
• Fix the radio (some speaker wiring must be shorting somewhere, cos no sound comes out)

Headlining: The Toy Shop here in Auckland created their own fibreglass mould specially for XJS headlinings, and their price is....... $1,800.00 plus GST. It's slightly cheaper to ship a new headlining from the other side of the world.  

Auto: I went to see an automatic transmission place, and regrettably I've booked the Jag in with them to give its ZF 4HP22 auto a birthday. The auto has always been a bit noisy and a bit rough during my ownership, and I guess I tempted fate by having the fluid changed and occasionally driving like I just borrowed some oil paintings. It kinda sucks to be spending money on an automatic transmission, but manual parts cars don't exist, and manual conversion kits only exist for the V12. Tell me I should spend more money on a Chevy LS swap and end up missing Nats here.

I did manage to improve the drivers window operation by flipping the rubber guide seal around, and I lubricated the passenger side central locking so much that it might actually work reliably for once.

For the radio, I wasn't lucky enough for the problem to have been caused by speaker wiring. It was caused by water leaks. 

This quote from the XJ-S Barry Bible will explain:

Quote

CONDENSATION DEFLECTOR SHIELD:  Apparently, either plugged condensate drains in the A/C system or leaking heater cores have a tendency to dump water on the stereo -- and some of those stereos ain’t cheap!  So, Technical Service Bulletin #8685 says essentially that a “condensation deflector shield” must be installed on all XJ-S vehicles prior to VIN 163790 whenever the mechanic is working in the area.

Can you believe the official fix for various disastrous design decisions in the A/C system is to fit a condensation deflector shield? Guess whose car is prior to VIN 163790 but isn't fitted with one. 

As part of diagnosing this, I dug out an older head unit which I originally bought for my Alfa ~15 years ago, and as an extra bonus I discovered my missing Iron Maiden greatest hits CD was still in it.  I strategically taped over some of this head unit's vent holes to keep any water from getting in, and I figured I'd run it in the Jag for a while.

Then I took apart the faulty head unit and cleaned the corrosion....

I reassembled it and set it up on a test bench running off an AC adaptor...

It makes noise again! Jolly good show. Now I must build a condensation deflector shield. 

[Thousand Dollar Supercar]

The verdict from the automatic transmission place was that the problem under hard acceleration wasn't caused by the auto! I was saved from having to spend lots of money on it.

When the problem started to develop, it was only apparent at the top of second gear - it felt like the transmission wasn't making it into third gear, but in fact it must have been the engine running out of gas. Once again I'm lucky I didn't blow it up.  I consulted the Barry Bible and apparently thirsty old Jags can suffer fuel starvation for several reasons:

• Fuel pickup blockage because the fuel tank likes to rust (my car has had a tank replacement in the past)
• Insufficient voltage to the fuel pump because of Lucas electrics
• Internal mechanical problems with the fuel pump

Barry has answers for all of these issues, and he hasn't put me wrong before. His first recommendation is to remove the strainer from the pickup in the surge tank and substitute an external filter instead. I went and bought the required 1/2" size of fuel hose and filter, which of course you can't get from Repco/Supercheap. Then I took out the fuel pickup aaaand.....

It's fine. 

I took it off anyway, because I'd already bought the parts to add the external filter:

Ideally I'd find a bigger transparent filter which can be disassembled and cleaned, but maybe later.

What's next... insufficient voltage. The voltage across the fuel pump turned out to be a constant 13.2V. That's presumably good enough - Barry said it should be at least 11V at idle.

So the remaining fuel starvation cause is this:

Barry describes this easy modification you can make to these fuel pumps to stop them playing up as they age. Yes you can just buy a non-Lucas fuel pump, but where's the fun in that.  Plus this Lucas part is actually a Bosch part made in France. Apparently it's easy to un-crimp the top of the aluminium canister and mash out the internals.... I didn't find it easy. Violence was required. Here's what's inside:

The part that does the pumping does not spin with the rotor. It has some internal impeller which is driven by the rotor, but the body of the mechanism needs to be held in place. The problem is that the only thing keeping it in place seems to be a rubber o-ring (not shown) pressing against the outer aluminium canister of the pump. As everything ages, eventually the part that does the pumping starts to slip and spin, meaning less relative speed of its impeller bits, meaning less fuel pressure. Then you get a crappy idle and fuel starvation at full power, and then you get burned pistons and you have to do a 350 Chev conversion. 

So here's the solution:

how?

By cunningly fitting a screw into the inside of the housing of the motor, we can lock the pump mechanism in position. The screw threads need to be ground off flush on the outside of the stator/casing so it can be jammed back inside the aluminium housing of the pump. By using the right number of washers under the screw head, it's impossible for the screw to come loose and fall out once the whole thing's reassembled. Genius.

It was not easy to get the pump back together. It looks all mangled now and I'm surprised it still works and doesn't leak. 

I also replaced the regular fuel filter at the same time, because it had been installed over 14 years ago. Then I went for a drive, and yay, it seems to be fixed!  The idle seems to be improved, which is something that has always bugged me.

Most importantly I seem to be able to use full throttle right to redline again without the awesome AJ6 drinking its injectors dry. It's all the horsepowers that do it. Listen to them all on my crummy hand-held dashcam:

All this mucking around has meant I still haven't changed any suspension bushes / subframe mounts or fixed the headlining. Hopefully I can fit some of those in by Nats. 

[Thousand Dollar Supercar]

On 17/12/2023 at 13:04, Thousand Dollar Supercar said:

I'm becoming more of a Jag man as time goes on.

Check out my latest Jag-cessory:

It's someone's scody old lighter, covered in 'brown lizard' and tobacco stains. 

But wait, when you clean it up, what does the engraving say....

Yep, it was once owned by Mister J.A.G. 

How good will that look next to my keys on the bar of the local TAB. 

 

[Thousand Dollar Supercar]

Boring update: I finally changed the rear subframe mounts.

Here's the one I had been most concerned about. I had expected to find it in worse shape once it was off the car. Hardly worth worrying about really.

This rubber-to-metal bond is the only thing that seems to keep the IRS assembly attached to the car. There is a radius arm connected near each rear hub which twists the whole IRS assembly in its mounts as the car leans in the corners, creating a passive rear wheel steering drunken snake effect. Wikipedia says this "...may result in significantly improved handling". May?  Anyway, the mounts can fail from age or too many burnouts, and then you definitely won't have significantly improved handling.

In this shot, the two subframe mounts have been removed:

You can see the IRS cage thing, the tricky double shocks and springs, the light reflecting off the inboard rear brake disc, the skinny anti-roll bar terminating at the base of the RH spring (not present on all XJSs)....

You can also see that I managed to change the mounts without disconnecting anything such as the exhaust, brake lines, roll bar, driveshaft, radius arm etc. I did one side of the car at a time, using a jack and an axle stand.

New mounts fitted (this is on the opposite side of the car, to mess with your head):

Now that these mounts are done, I'm not gonna be THAT guy:

 

[Thousand Dollar Supercar]

 

After running fine during Nats, the Jag has started doing its fuel-starvation-at-full-power thing again. 

@h4nd had already pointed out that the commutator in my fuel pump had looked pretty worn. Here it is at 100% scale in the only photo which I hadn't already resized to low res:

Looks like it has done 36 years of service. I guess all that missing copper was caught by the old fuel filter and isn't still inside my fuel system somewhere..

I bought a new fuel pump, which is supposedly for the XJS though it's slightly smaller and has a different style of terminal:

Annoyingly, nothing changed! The problem is still present with the new fuel pump installed. This probably means that the old pump was never the cause in the first place, even before I performed the mod to stop its impeller housing spinning. 

I'm still working under the assumption that the problem is caused by fuel starvation rather than by ignition, because surely if the coil was too weak to provide enough sparks at high rpm, there would be all kinds of backfires from the unburned fuel? My old Alfa would cut the spark to limit engine rpm, and when I hit that limiter too aggressively, it would just about blow the muffler apart.

I guess I could have a partial blockage anywhere between the pump and the injectors, or a problem with the fuel pressure regulator (which is controlled by manifold vacuum), or maybe the ECU is actually bringing in a rev limiter when it shouldn't.. I think I've noticed the rev counter spaz in the downward direction in response to the problem occurring, but generally you want to keep your eyes on the road when nearing redline, and you instinctively back off instantly if the engine starts doing strange stuff.

I still have the other issue of the engine not running smoothly at idle and low rpm - when you're under the bonnet you can detect an intermittent shaking of the motor like a partial misfire, up until the point where the rpms are high enough to mask it.

I don't know how to proceed with the diagnosis. Any ideas? Might have to take it to somebody who can actually measure stuff (exhaust CO, fuel pressure, injector duty cycle or whatever)?

[Thousand Dollar Supercar]

I changed the ignition coil to see if it had any effect. The one which was in the car looks to have been made in 1995. If it is a Lucas DLB198 coil as suggested by its mounting bracket, its secondary resistance was measuring below spec.

The new coil is branded "Flame-Thrower", which sold me on it immediately. This should be its theme song.  

Anyway, it didn't make any difference. The car's intermittent stumbling idle remains, and its misfiring near peak power seems to be getting worse. I read a bunch of forum threads of other people who have tried to crack the bad idle problem with their AJ6 or AJ16 (the revised version of the same motor), and most people seem to test and change a bunch of stuff then give up (the threads just stop). I did find one thread where someone actually fixed it, and the problem in that case turned out to be several exhaust valves which weren't sealing well.  The guy took the head off and got the valves reseated or reground or whatever, and then the car idled properly.

So.... I wonder if I could have some partially burnt valves or weak valve springs or worn cam lobes or something. I did another compression test today and got similar slightly-too-high readings (190, 183, 190, 180, 188 and 190psi) to the last compression test. Might be my gauge. The spark plugs looked fine. I gapped them down to factory spec, no improvement.

I have recently acquired a detailed factory document all about the engine management on the later 4.0 AJ6 which gained oxygen sensors (so many variants of this motor, grrr). The guide has taught me that my fuel tank vacuum pressure relief valve has no vacuum line connected to it:

I don't know why there would be a valve if there's no vacuum line for it. Maybe it's for other markets / I hope the vacuum line isn't sitting somewhere disconnected and leaking air.

This new guide has given me a thousand things to check. For example, the ECU controls ignition timing and fuel mixture based on airflow and crank position, with a compensation factor for throttle position and coolant temp and air temp, and now I have a bunch of expected voltages and resistances and oscilloscope waveforms for all of this. I just need the motivation to spend weekends chasing my tail.