1991 Jaguar XJ-S

[GMJohnny]

AK,

Reading your post reminded me of trying to fix the tach in my ‘65 442.
The tach wouldn’t perform correctly with the Pertronix set up in it, but
it would work correctly with the points ignition. If I recall correctly, a Tach
Adapter was required to make the signal correct. The question I have is:
Has there been an ignition modification which is causing the tach to
malfunction? I don’t know if you’ve looked at it that deeply, but that may
be some of the issue.


GM

[AKROVER]

I see no evidence of modification. The distributor, amplifiers, coils, and wiring harnesses all look right. The signal going to the tach looks like what I would expect on the oscilloscope. And no one offers performance upgrades for my ignition system. I keep dreaming about ways I might upgrade it someday, but 12-cylinder ignition timing isn’t a matter to take lightly. The distributor actually has neither vacuum nor centrifugal advance. The computer has a vacuum sensor and an engine speed sensor on the flywheel that it uses to determine spark timing. The distributor requires precise alignment to accommodate the full range of advance without having too big of a gap between the rotor and the plug wire conductor. It is a clever system, but quite unusual.

It is snowing and the ground has turned white. I think Jaguar season is officially over. The fun projects can now begin.

[MostMint]

crank trigger, coil packs and megasquirt will get you upgraded

[AKROVER]

crank trigger, coil packs and megasquirt will get you upgraded

I had incorrectly assumed that nobody could handle a V-12. Megasquirt is an option. The wheels are turning in my head.

[AKROVER]

I wasn’t really expecting to put this together this quickly. The cracked wood on the center console was a constant reminder that the car was old and imperfect. I had been looking forward to figuring out what to do about it. I had many ideas. Kris made a good point about the ashtrays being this totally weird period correct thing, but a part of me really wanted to cut those out and put in cup holders. While in Rapid City yesterday, we stopped at JoAnn Fabric and bought some black vinyl that reasonably matches the dashboard grain pattern. It was merely $10 per yard in 54” width so I bought enough of this material to do this job a dozen times.

This morning, I began the disassembly. The center console has been disassembled before as a few of the plastic snap tabs on the cigarette lighter and the speed control switch were broken, and the cigarette lighter bezel was glued down on one side. The wide flat piece, known as the ski slope in XJS parlance, is a steel plate with real wood veneer glued to it. The cracked veneer scraped off easily with just a bit of sanding to remove some of the old adhesive. It was a sad thing to see this luxurious treatment coming to its end in life.

I wasn’t going to tackle the vinyl today, but after lunch, I brought the metal piece in and began to see a reasonable path forward. My idea of cupholders looked quite challenging as the slots for the ashtrays are longer than the diameter of any drop-in cupholder. I would have had a gap to fill in on the steel plate, not to mention a hole saw cut without a solid center to get it started. With so much vinyl material available to me, I figured I should experiment and then I could always change my path in the future.

I cut a piece of vinyl and then sprayed it with Gorilla glue, which I had just noticed was not recommended for vinyl. I sprayed a little heavy in a few places and the vinyl looked like it was beginning to dissolve, but I pushed forward because it was just an experiment. The vinyl adhered beautifully to the metal plate and even the ‘dissolved’ sections later seemed to stretch back out and lay flat. I cut out all of the openings and the glue held. I cut the front edge and the back edge flush as they both have overlapping trim pieces. I cut the side edges about an inch long and then flipped the assembly upside down to give a spray of glue to both the excess vinyl and the metal underneath. After letting the glue dry for a minute, I folded the vinyl under and it not only stuck well, but it flattened out perfectly.

After dinner, I realized that my first experiment in putting vinyl on the ski slope looked so good that I should just reassemble it in the car, just to see if I like the black vinyl. The only thing that didn’t go well is the cigarette lighter. I will either need to glue it down like had been done before, or perhaps I can add a couple of small screws to hold the bezel down. The ashtrays were challenging as there is a clamp that holds them to the ski slope. I should have installed those first. Once the ski slope was back in the car, I had to use a nylon strap to hold the clamp in place while I started the screws in the bottom of the ashtray assemblies. Then I had to force the strap to slide out before finishing screwing the clamps tight. The strap was tight around the ashtray once the screws were started so I was concerned that I was going to pull up the vinyl I had just put on, but it held, and I managed to wiggle the strap free. This really is the kind of problem solving that makes working on a car so mentally engaging. Of course, it helps if you put things together in the right order, but in this case, it was an easy trap to fall into because the assembly order is not just the reverse of the disassembly. The ashtrays are the first thing to come out, but they really should go back in with the ski slope still out of the car.

I should point out that prior to 1987, the center console of the XJS was black, not wood. This isn’t an original idea. The contrast, though, almost adds to the interior, carrying the black further down and directly contrasting with the tan, which also happens where the A-pillars meet the dashboard and a bit on the lower dash. This is not perfect, but I will say my jaw was completely dropped when I stood back and looked at this quicky experimental job that cost all of a couple bucks in vinyl and glue.

Before image

After

Wider look at the interior

[GMJohnny]

That looks so good! How soon before the rest of the dash is blacked out?!!

GM

[Basement Paul]

That did turn out really well. I would just go buy a Yeti that doesn't leak when it's upside down instead of putting cup holders in there. Looks too cool the way it is.

-BP

[AKROVER]

This weekend, I disassembled the dash. I had three missions, to fix the outboard passenger vent, remove the wood panels for refinishing, and extract the tachometer. It is also always a good reconnaissance mission to get a better view of the inner workings and assembly. Once again, I am impressed by the condition of my car and the overall simplicity of working on these Jaguars.

I made one mistake. I tried to remove the entire dashboard assembly. It is one large piece. I watched a video of the removal in an older vehicle. There is a support bar that runs across the bottom of the dash that in older vehicles ran straight across. That meant that removing the dash in older vehicles required removing the steering wheel. My vehicle has a big loop in that support bar that is clearly intended to loop over the steering wheel, but I either didn’t have things taken far enough apart or I simply couldn’t figure out the right angles as I couldn’t remove the dash. It was a good learning experience, plus my goal wasn’t actually to remove it, only to gain access to the backs of the wood panels which I was able to do easily with the dash still looped around the steering column. I felt pretty stupid, though, when I looked at the back and saw that the wood panels were on spring clips and simply needed to be pried out gently. My mistake was caused by removing the glovebox panel first as that one is screwed to the glovebox door, so I assumed all the panels were screwed. I have now remounted the main dashboard, although I still have a lot of reassembly of the electrical components that I unnecessarily disconnected in my attempt at complete removal.

There are six wood panels, the glovebox door, the center vent surround, the two outboard vent surrounds, and the two switch panel surrounds on either side of the trip computer. The switch panel surrounds are veneer on metal like the center console was, but they are in good shape and should require no refinishing unless my work on the other panels causes a visual mismatch. The other panels are all veneer on wood. The outboard vent surrounds are also in good condition with only a few minor cracks in the lacquer finish that aren’t particularly visible on the small surfaces. Depending on how the refinishing goes on the two bigger panels, I might just leave those as is. The center vent surround and the glove box panel are the ones that clearly show cracking in the lacquer finish. Those are now on the bench awaiting refinishing.

[AKROVER]

The outboard vent ductwork was pushed down by some of the wiring that looks like had been disturbed by previous work. I tried to bend the wiring back up and I was able to get the vent reconnected. I might try to put some support in for that mass of wire so that it doesn’t knock the duct off the vent, but I don’t think that is what happened. I think someone was in there working and when they couldn’t get the vent lined back up, they just threw it together. At this point, the vent is connected, and this problem can be considered solved.

[AKROVER]

The instrument panel was a little tricky to remove. Old plastics warp and old vinyl gets sticky, so it didn’t slide out as easily as I expected once I removed all the screws. The panel is entirely electric (no mechanical speedo cable), so it is just a matter of two wiring harnesses that have to be disconnected once the panel slides enough to get a hand behind it. The entire panel is now sitting on a table in my office and the tachometer has been removed and is sitting on my desk. The instrument panel has two interesting stickers. One is an assembly part number that appears to match the part number others have listed for the 89-91 XJS’s (DAC 6194). The second sticker has four digits, 0491. In seeing these same stickers on other assemblies online, it appears that those are date codes, likely week and year like a tire date code. That date code would imply that this is likely still the original instrument panel. The speedometer/odometer assembly has its own sticker, 2890, which could simply mean that the assembly was in stock when it was assembled into the panel, but it isn’t necessarily conclusive that this is the original speedometer/odometer (such is the way with classic cars, no one really knows the mileage with any certainty). The tachometer has its own sticker, 1387, which would imply that this is the wrong tachometer. When I removed the tachometer, there is black magic marker writing on the back of the face that says, “88 XJS”, again implying exactly what I had been guessing, someone put the wrong tachometer in my car.

I agonized over what to do about the tach. I thought about fitting an aftermarket tach into the dash. I thought about buying a used complete instrument panel that popped up on eBay from a salvage yard that appears to be from a 1990 car, but the seller does not know if any of the instruments work and they still want $250. I then dove deeper into the electronics on the tachometer. While no one has ever documented a solution to my problem, there are documented solutions for converting 6 pulse per revolution (ppr) tachs to 4 ppr for people doing 8 cylinder swaps. That provided some mathematical clues, but other British car owners have faced engine swaps from 4 to 8 or 4 to 6 and someone figured out a lot about the electronics of these tachometers that are used by several British automakers. While the electronics on mine looks different thanks to the inclusion of surface mount resistors in the late 1980’s, the main chip appears to be the same which means the basic circuitry is the same. It appears to come down to one capacitor value. For going from a 4 cylinder (2ppr) to an 8 cylinder (4ppr), they needed to cut the capacitance in half. I am going the other way which means I need to double the capacitance. Based on the clues from people swapping Jaguar 12 cylinders for V-8’s, and based on the documentation provided by this clever MGB owner, I am nearly certain that I just need to add a 0.1uf capacitor in parallel with the existing one. If we still had Radio Shack stores, this would have cost me less than a buck to give it a try. With online ordering and with some uncertainty about the capacitance value needed, I ordered a kit with 150 capacitors of various values, including 10 of the one I think I need. That kit cost me $16 which is still a cheap fix. My other option was to buy 20 of the one I think I need for about $7, but an assortment solves the uncertainty problem and might even allow me to dial in the accuracy by using a couple of smaller capacitors to get the reading more exact.

I had already wasted many brain cells on how I could test a tachometer so I was already contemplating buying a pulse generator to inject a fake signal into the tachometer to verify both operation and calibration. When I bought my oscilloscope, I was excited that it had its own built-in signal generator. I had originally hoped to use that, until someone else reported that the minimum pulse for the tach was about 6 volts and my oscilloscope signal generator maxes out at 3V. The MGB owner, though, had identified a point in the circuit after the input signal conditioning where he was injecting a signal from an MP3 player, of all things, as his calibration signal. He indicated that at that point in the circuit, the pulse was already reduced to about 1 volt, well within the capabilities of my oscilloscope. It took some effort to set up the test, but in the comfort of my office with the tachometer in my hand, I was able to prove that this one is calibrated for 6ppr by injecting signals of 200hz, 400hz, and 600hz, which gave me tach readings of 2000rpm, 4000 rpm, and 6000rpm. The tach actually read slightly low, like maybe 5800rpm instead of 6000. By having my own test setup, I will be able to verify that my modification works as expected for my 3ppr ignition signal.

One funny thing to note is that I have spent countless hours searching the internet for solutions to my problems, but a recent search included my own post on TireSmoke on the first page of results. I am now starting to show up in my own searches, which could be good if my memory starts to slip. It does motivate me to better document my own findings as other owners might just stumble upon this.

[AKROVER]

I experimented with an idea for fixing those cracks in the clear finish. I had read that the finish on the wood panels is lacquer, and lacquer can be reworked usually just by applying lacquer thinner. The finish on older Jaguars might have been lacquer, but mine is not. It did not soften at all with lacquer thinner. I will have to sand those panels down and apply a new clear coat, probably polyurethane. Hopefully that won't affect the color.

[GMJohnny]

I experimented with an idea for fixing those cracks in the clear finish. I had read that the finish on the wood panels is lacquer, and lacquer can be reworked usually just by applying lacquer thinner. The finish on older Jaguars might have been lacquer, but mine is not. It did not soften at all with lacquer thinner. I will have to sand those panels down and apply a new clear coat, probably polyurethane. Hopefully that won't affect the color.

I’ve used clear spray paint on wood before and it doesn’t yellow the wood like urethane wood.
In your application, clear enamel ( or lacquer ) may be an option for you. ( I painted my wood
mantel with clear lacquer and the color remained the same. ) Both of these can be found in
aerosol cans.

GM

[AKROVER]

My capacitors arrived. I couldn’t figure out a test rig, so I simply soldered in the capacitor I thought I needed, figuring it wouldn’t be too hard to undo that if my calculations were wrong. I then injected a test signal and the results were a little mixed. The tachometer was exactly on at 2000 rpm (100hz signal). With a 300hz signal (6000 rpm), the tach reads high at about 6600. With a 60hz signal (1200 rpm), the tach reads low at about 1000. Since I never tested low signals originally, I don’t know if my modification introduced some nonlinearity or if the tach is just fundamentally flawed. I didn’t think the inaccuracy was meaningful so I installed it in the instrument panel and then installed the instrument panel in the dash.

I have completed reassembly of the dashboard, except for the two wood panels that need to be refinished. I did start sanding a little to see how deep those cracks in the finish run. It is going to be a tedious sanding project to get deep enough without burning through the thin wood veneer. Prior to reassembly, I noticed that the glove box liner was sagging. I sprayed that with some Gorilla glue, and it now looks pretty good for its age. There is some similar liner material on the dash beneath the instruments that was also pretty lose so I glued that, too. Before installing the glovebox, I was able to fish some zip ties under the heavy bunch of wires that were resting on top of that outboard passenger duct. The duct is now free of stress and the vent and wood surround are both back in place. I reinstalled the lights and electrical devices in the dash and tested most of them. I was reasonably organized with the parts and screws I removed, but I made a couple of mistakes on the order of reassembly, which made a little extra work for me.

After reassembling everything, I took the car for a drive (it was 55 degrees and the roads are dry). The tach was reading 1000 rpm while idling cold. I managed to get the needle to swing all the way to 5500 on a spirited bit of acceleration. When I got home with a warm engine, the tach was reading 700 at idle which I am sure is a couple hundred rpm lower than actual. I am pretty excited to have solved this problem with a ten-cent part, although I now have 149 additional ten-cent parts to store somewhere (on my way to full-fledged hoarder).

The red thing is the 0.1uF capacitor that I added to change my tachometer from 6ppr to 3ppr


It is nice to have the needle sitting twice as high while driving

[AKROVER]

I have been slowly sanding down the glovebox panel. I purposely am working a little bit at a time because I am concerned about me getting too aggressive and sanding through the veneer. The good news is that the dust color changes from white to brown when I finally get through the clear coating. This makes it easy to be aggressive with the clear coating. The cracks in the clear coating extended into the veneer so I have been forced to sand the veneer to erase those zebra stripes. Some of them might not fully erase, but most of them are now looking really good. The veneer is in good shape, and it is beautiful burl elm, so it is worth this effort to try to save it. I still have a few more sessions on the glovebox panel and then I have the center vent surround panel to start. I will probably have these ready for refinishing in about a week. I haven’t yet figured out what I will use for the finish.

[AKROVER]

I spent a total of about five and a half hours on sanding those two panels, mostly just a half hour at a time. The cracks did go into the veneer. I seemed to have some success in reducing the visibility of those lines by sanding deeper, but I was concerned about sanding all the way through the veneer. I tried hardest on a few perimeter cracks to see how far I could go and never achieved erasure, so I am confident that I did the best that could be done with the material I have. The final result is less than perfect but eliminating the cracks in the clear coat is a huge difference. I can see the lines in the wood, but only when looking closely.

Yesterday, I declared an end to the sanding efforts and began finishing efforts. I ended up buying spray lacquer. My research didn’t really uncover a compelling reason to choose one clear coat over another, but generally it seemed to me that lacquer was the right choice for the application. I sprayed five coats and then let it dry overnight. This morning, I was pretty excited by what I saw. The wood is beautiful, but the finish is not as glassy as the original finish. I am not sure I like that glassy finish better. It almost makes real wood look like plastic, but I do think there is merit in taking a couple more steps with the lacquer. I need to get some ultra-fine sandpaper to level out the finish, although it self-levelled decently on the flat surfaces. I then think the next step is to add a couple more coats and then finally polish.

I set the two pieces in place on the dash, and they do look awesome from just about any angle, but the glassiness of the other pieces I haven’t refinished does create a visible mismatch, particularly with the passenger outboard vent surround that sits right next to the glove box panel. If I can achieve some better glassiness on my work, then I think the mismatch won’t be noticeable. If I can’t, I think the solution will be to refinish those vent surrounds (well, at least the passenger one). No matter how this ends, this is going to be an upgrade. It really does look nice.

I drove the car on Saturday. I was going hiking in Wind Cave but planning to park at the campground which has a bison exclusion fence. The temperatures climbed to near 60 that day and we haven’t had any snow in a long time, so the salt dust has mostly dissipated. The car ran great. I was relieved that my dashboard disassembly and reassembly hadn’t created any new problems. We have so much sunny weather through the winter here that it is going to be tempting to drive it. The heater worked nicely on the drive to the park (I opened the windows for the slower parts of the drive home).