1991 Jaguar XJ-S

[AKROVER]

I wasn’t going to pull the door skins just for this lock issue, but as I used the key a few times to lock and unlock the car, I realized that things were really stiff, not quite break the key stiff, but close. BP was right, I needed to lubricate the locks and window tracks. I was right, the issue with the locks was lubrication. The position switch is actuated by a rod attached to the key lock. The key lock is linked to the latching mechanism by a rod. The latching mechanism is linked to the interior lock lever by a rod. The motor is somehow attached to the interior lever. That puts no less than three linkages between the motor and the position switch, and everything was very stiff. Things move very smoothly now and the power locking system works reliably. Problem is resolved.

[AKROVER]

The new sun visor clips arrived. I quickly found out why the old ones had broken off. There is something wrong, either the clip part number or the sun visors, themselves. The clips were way too tight. I had to file them to open them up so that the visors would easily clip in and out. I hate taking a file to a couple of cheap pieces of plastic that I just bought for $53 combined, but there was no way those were going to work as they came out of the packaging. It is nice having the visors secured now and the color seemed a perfect match. Problem resolved.

[AKROVER]

Since I was working overhead, I decided to take a look at the dome light. I pulled down the assembly, pulled out the bulb, and then tested the connections. I found no power to the fixture. Since I couldn’t figure out how to troubleshoot wiring behind the headliner, I decided to just put it back together with a goal of getting the fixture to sit more level. As I pushed the assembly into place, the light came on. I have no idea what I did to fix this, but it seems likely that the ground wire was loose, and I somehow reconnected the ground just by playing around with it. Not only is the light now working, but it is also sitting a lot nicer. I will consider this problem resolved.

[AKROVER]

I registered my car. I really like that I have yet to find a line at the treasurer’s office. I also like the fact that it is one stop for title and registration. I am not overly thrilled with paying sales tax on a 33-year-old car, but at least it is only 4% here. I had four options for plates, regular, custom, historic, or use a 1991 plate with the historic registration. The 1991 plates are just as ugly as the new ones and don’t even have the year on them. The historic plates aren’t exactly attractive. Historic registration either way adds annual mileage reporting and a few extra dollars. I couldn’t come up with an exciting custom and it was just going to be printed on an ugly SD plate anyway, so I just put on regular plates. I think with historic plates I could have avoided a front plate, but the front bumper has holes and a recess for a plate, so this is one car that looks better with than without.

[AKROVER]

My new ignition key arrived a couple days ago and it works. My new key blanks arrived today. Ace Hardware cut them for me and they work. The new key blanks were the thin-flanged universal key for my car, so they work all of the locks (the thick-flanged valet key only works the doors and the fuel door). The old universal key was bent so it will not squeeze into the glove box lock. The new keys now allow me to lock the glovebox. The bent key does work in the trunk, but the trunk lock is bent so that is likely where the key got bent. The new keys work the trunk just fine so the lock isn’t that messed up. I get pretty excited about solving stupid problems. I now have two sets of fully functional keys (only one valet key). Getting that second set of keys cost me $62, including tax and shipping. My new keys don’t exactly match the original key logos so I will use those as my functional set rather than the originals.

I also have two original Jaguar key rings. One came with the car and is engraved with the original dealer and phone number. The phone number is still used by Kempthorn Motors, but it is currently area code 330 instead of 216 as shown on the fob. The 330 area code was created in 1996 which further supports the key ring being original. The other Jaguar key ring is one I received from Jaguar Cleveland when I bought my 1999 XJR. Some eBay sellers list this one as late 80’s through early 90’s, so period-correct for my current car but not the ’99. Perhaps Jaguar Cleveland was just sitting on some old key rings when I got my car. On eBay, I see that key ring listed from $50 to $150, not that anyone is paying that much for them. For the other one, I have found some similar dealer engraved key rings on eBay listed for $25, but I haven’t found an exact match. Those might not be original Jaguar promotional key rings. Those might be something dealers purchased through other channels. Either way, both add a little interesting history to my car. Perhaps a future owner will find this as interesting as I do.

[AKROVER]

The fuel odor in the trunk seemed to be getting worse so I tore into the trunk yesterday to investigate. To my relief, the fuel system is very clean. Rusty tanks and lines are the scary problems with fuel odors in the trunk. I was also happy with the layout of everything. I hadn’t realized that the fuel tank sits up high behind the back seat and over the differential. This allowed Jaguar to use an inline fuel pump mounted low in the trunk. I had to start the car to find the leak. Once pressurized, I noticed a steady drip coming from the outlet side of the fuel pump. I disconnected the outlet hose and cut it a little shorter to give the hose clamp a new bite. It still leaked. This morning after a stop at the parts store here in town, I replaced the entire line between the pump and the filter, including replacing the hose clamps. It still leaks. Throughout this process, I kept watching underneath the pump with my new inspection camera and it really looks like the pump housing is leaking rather than the hose connection. I still find that hard to believe, but a new pump is on the way, along with some better high pressure hose clamps. The pump that is in there is the original.

Jaguar has such a bad reputation, so I am continually surprised at how straightforward everything has been I have had to pay ridiculous amounts of money for cheap plastic interior bits, but the mechanical parts continue to be cheap and readily available. The fuel pump is used on dozens of different brands and models. I could get a cheap Chinese pump for less than $20, but I did spend a hundred getting a Bosch as the cheap ones have a reputation for being noisy.

[AKROVER]

Today my new license lights arrived. I couldn’t bring myself to pay $100 for the originals and it doesn’t make sense in the modern world. I took a few measurements and surfed the internet until I found some aftermarket LED license lights that had dimensions I could work with. By a funny coincidence, they were Jetta lights, but they were an earlier generation of Jetta than mine. It was a relatively easy project. I used my new soldering iron to attach wires and my new crimping tool to put on ends that would work with the existing wiring. The spade ends had to be modified as the originals were not as wide as normal spade connectors, so I used my new rotary tool to fit those. I had to drill a couple of holes and then screw the new light into place using the original housing. There is a gap and I did add a couple of plastic pieces over the gap. This is not a fully sealed assembly, but this is not a rain car.

Final installation


Old vs New


They work

[AKROVER]

The fuel pump arrived and I installed it. The electrical connections had to be changed. I had to fabricate a rubber mount for the pump as the old one was glued to the old pump. I adjusted the hose length of the new section of hose I put in the other day which improved the routing. I installed a new “fuel injection” hose clamp on the outlet of the pump. I also adjusted the mounting bracket to allow the pump to sit at a slightly less steep angle to allow the outlet hose to bend less abruptly against the floor of the trunk. I fired the car up and found no leakage. I have not test driven the car yet as the roads are wet right now (heading into better weather tomorrow). I don’t see anything obviously wrong with the old pump, but I have solved the serious dripping leakage, so I don’t think there was any downside to replacing the pump. The rate at which it was leaking was significant; I calculated roughly a tenth of a gallon per hour while pressurized and likely still some loss with the pump off. I have marked this problem as resolved, but I will be monitoring it to verify that. I was confident enough to put the entire trunk back together (spare, carpeting, fuel system cover, and battery cover).

It was the first time I had pulled the spare tire out and the date code on that one is 330 which is a pre-2000 3-digit date code which can only mean the 33rd week of 1990. The tire was made in Germany, which further supports the tire being original. I am sure this Goodyear V-rated tire is a collector’s item. Let me know if you are interested. It still holds air, probably the original air, if that helps.

My Amazon order today also included the Repair Operation Manual (aka ROM) for my car. It is 600 pages of schematics, drawings, and procedures for repairing most of the systems in the car. This was published by Jaguar, themselves, and was intended for their mechanics. This will help tremendously when I start diving into more complicated systems. It wasn’t cheap, but I suspect it will be money well spent. This thing is like a Haynes manual on steroids.

[AKROVER]

Armed with detailed electrical diagrams, I decided to diagnose the problem with the power antenna last week. When I applied power directly to the antenna, nothing happened. When I tried to remove the antenna, the rubber trim piece above the sheet metal was no longer flexible enough to simply pull off. In order to cut it off, I had to take apart the antenna assembly in place. The antenna was the original. Any cheap antenna will work in this car as there is a lot of space under the quarter panel. The new one arrived today, and it was an easy installation (took less time than getting the old one out). Jaguar has a strange configuration on the controls. There is a rather pointless time delay relay that holds the antenna up for about 10 seconds after the radio is turned off. That relay is a frequent problem, so I was prepared to bypass it. Surprisingly, mine still works, so I left it in which made the electrical installation really easy. I even used the original connector. The inner part of the quarter panel where the antenna mounts looks fantastic. So far, most of the dark corners I have worked in have looked great. The stereo system works reasonably well and likely better now with an antenna that actually extends. We don’t get many radio stations around here, but luckily I landed on some seemingly appropriate 80’s music for my test drive today. Another problem is resolved.

[AKROVER]

Problem#33
Status: Resolved
Description: Odometer stuck at 47000

The other evening, I was cruising to a distant gas station when I noticed the odometer was turning over to 47,000. Six miles later, when I got home, it was still turning over to 47,000. When I googled “XJS odometer stuck”, I found lots of reports. Several reports confirmed that it is a frequent problem at thousand-mile intervals. This is likely due to the load of turning the extra digits. There was a report of getting it going again with a hard thump and a report of having success just by going in reverse for a bit. One owner achieved merely temporary improvement with lubrication, but tearing into the dash is not something I was too interested in trying right now. One older post really appealed to me. The owner cleverly drilled a small hole in the speedometer window and bumped the numbers to get them moving again. When backing up and thumping on the dash didn’t work, I got out a tiny drill and drilled near the inside edge, out of the line of sight. I then worked a thin wire down in there and gave the numbers a bump. We are moving again. My odometer is now off by about 7 miles (that I know of), but that is now documented here. All of this means that I have already put 500 miles on my car. It is still running great and a lot of fun to drive.

[AKROVER]

I have been busy, but I have little to show for it. One of the more annoying things about this car is this tachometer problem. I started trying to track down the wiring, but it turns out that my new book skips over my version of electronic ignition. I found an electrical supplement online that I was able to download that finally pointed me in the right directions.

The electronic ignition system is a dangerously weird one. It is split into two systems, one for each bank of cylinders. The distributor has two coil wires and 12 plug wires. The rotor works in two different planes. There is an upper set of six outlet conductors that go to the spark plugs on one bank and a lower set of six for the other bank. Each has essentially their own rotor, but the rotor is just one piece. The dangerous part about this is that the fuel injection system is not similarly split. That means if there is an ignition system failure on just one bank, the car can be running as an I-6 while the other bank of cylinders is just pumping air and fuel down to the catalytic converter. This is one of two ways that these cars have been known to burn (the other being the usual leaking high pressure fuel lines that all fuel injected cars have as a risk).

There is a signal wire from one of the coils that goes to the tachometer through a 6.8K resistor. I found that wire and the resistor. I verified the resistor. The signal to the tach is a pulse signal so it requires an oscilloscope to read. Coincidentally (or not), I now own an oscilloscope. The oscilloscope confirmed a pulse signal.

A similar wire from the other coil feeds to a diagnostic socket that the dealers could plug into with an electronic diagnostic tool. I was able to ‘plug’ in my oscilloscope to see the pulses on that wire and got a similar result to what I saw on the other coil, but the voltages were much higher. Unfortunately, I had already sealed up the resistor so I couldn’t retest on the coil side of the resistor where the voltage would be higher, ideally the same as what I was seeing at the diagnostic socket. That left open the possibility that the amplifier that feeds the coil that the tach is connected to might not be putting out enough voltage to excite the tachometer. Rather than tearing back into the resistor, I switched the two amplifiers, which didn’t change the way the car runs nor the way the tach reads. Unfortunately, I also broke one of the mounting screws for one of the amplifiers in the process.

If I understand the system correctly, there should be 3 pulses per revolution going to the tach or the diagnostic socket. Each is part of a separate ignition system for each bank of 6 cylinders, and each cylinder fires once every two revolutions, so each coil is fired 3 times per revolution. On the oscilloscope, I am measuring my idle RPM at 1300 (should be 750). This means that my tachometer is further off than I thought. I will need to look at that idle speed more closely as that is too high.

As for the tachometer, I will need to tear into the dash to further assess. There are reports of grounding issues in the instrument panel causing bad readings, so perhaps that is the problem. I have a couple other reasons to open up the dash, so perhaps I will get to that sooner rather than later.

[AKROVER]

While I was playing around, I recorded a rolling start 0-70 run, in case anyone wants to hear what my V-12 sounds like in the cabin. I had my foot to the floor and I manually controlled the 1-2 upshift but I have no tach, so I was conservatively shifting on feel. I shifted to 3 (D) and lifted when I hit 70. I think 2nd runs out to about 85. The recorder was mounted to the center console between the seats probably 8 inches lower than shoulder. I was wearing a winter coat so there is some rustling noise from my shifting movements, but barely noticeable. At the end, you can hear some of the tire slap on the sections of the road to put the noise levels into perspective. It is tall gearing (2.88) so not a very impressive 0-70 time.

https://take4digital.com/Jag0-70.mp3

[GMJohnny]

It’s cool that it has its own distinctive sound. My ‘66 442 with the tri-carb had a very different induction sound which made it nearly impossible to keep your foot off of the go pedal! When driving, it was more fun to listen to the car than the radio!

GM

[Basement Paul]

Kind of sounds like a V4 motor cycle with a stock exhaust to me. Definitely a distinct sound.

-BP

[AKROVER]

I think I have figured out the tachometer problem. I think someone replaced the tachometer but bought the wrong one. Tachometers do commonly fail, and I am now reasonably certain that there are two different tachometers that Jaguar used. One was for the early ignition systems that were more conventional in their design and so produced 6 pulses per revolution in the tach signal. The other one is for my electronic ignition system that produces only 3 pulses per revolution in the tach signal. Yesterday, I was driving at 70 mph and noticed that the tach was reading steady right around 1300rpm. When I got home, I calculated what it should have been reading, and the answer is 2600rpm. I am off by exactly a factor of two. Chances are that neither a tired tachometer nor a grounding issue would cause such a precise result.

There are no tachometers for my year on the market right now. There is an eBay listing for a tach that indicates it fits older cars (through 1988). It indicates a part number that matches the number on the faceplate of my current tachometer. I found a sold eBay listing for one for my year and it had a different part number. I am not convinced that those faceplate numbers are actual assembly part numbers, but it adds to the evidence.

The bigger question is what to do about it. The older tach on eBay is listed for almost $500 so if I could find the correct one for my car, I could likely sell mine to cover some of the cost. But there aren’t any right now, so perhaps the correct one for my car is rare. There are also some full gauge clusters with tachs listed right now for the older cars, but none for my year.

One solution would be a simple frequency doubler. As someone who supposedly has a degree in this stuff, I should be able to design a simple circuit for less than $20 in parts, but I will spend hours in design and assembly. Dakota Digital has a tachometer calibration device that can act as a doubler. It is slick with a Bluetooth interface. The price is only $113. It would have an advantage of being useful in an engine swap or even a gearing change as it can handle both tachometer and speedometer calibration in the same device. With either my own circuit or the Dakota Digital option, I would have to find a place to mount the frequency doubler and to get power and signal wires to it.

Another solution would be to tie the tachometer into a 6-pulse per revolution signal. The signal going from the ignition control to the fuel injection control is just that, but the location would make it difficult to tie into and it might require electronic isolation and possibly a boost. I might also be able to combine the current tach signal with the diagnostic socket signal as the two 3-pulse signals should be completely out of phase with each other, but the combiner circuit would need to provide isolation between the two inputs. I should be capable of such electronics design, but the wiring would be painful.

Another solution is to modify the existing tachometer. It is a relatively simple design, and it appears that the answer is merely one resistor and one capacitor. This would require disassembly, gaining a deeper understanding of the circuit design, calculating the values, and installing the components. The final cost is untold hours, but about $2 in parts. Again, my degree implies I should be able to do this, but I haven’t done any electronics work since the 1980’s.

Another solution would be to install an after-market tachometer. Mine is essentially a 6-cylinder tachometer so almost any option on the market would work. Mounting one would be the challenge, but it is possible that I could fit one into the factory location with some cleverness. It would lose the appearance similarity with the speedometer, though.

Another option would be to live with it. Now that I understand what I am looking at, it likely provides adequate information, just without much needle sweep. It is likely half right all of the time.

The next step is to tear apart the dash. The forecast finally is starting to look like winter so once the first salt hits the local roads, the Jaguar season is over. There is a chance that could be tomorrow, but I think they have backed away from forecasting accumulating snow and we don’t get salt on the roads until it is truly necessary. I have a few projects to get to once the car is parked so that is something to look forward to. I have already fired up the heater in the garage once and it is working well. For now, the Jaguar is still drivable which is nice. We even drove it to the grocery store yesterday.