jag-reflex, thanks for the rotor suggestion. Seems the mechanic and I had that discussion (I know he replaced the cap), but I'll ask about it again.

89 Jacobra, you're correct, I am having a professional do the work, he's taken care of that cat for about 15 years or so. Unfortunately, I'm not mechanically inclined enough nor equipped properly to do the work. Sure wish I were.

The big question in my mind is how can the automobile be running well on a test drive after repairing some valve cover leaks, a valley cover gasket and an oil sender, sit for 4 days and then have a miss on the test drive before returning the car to me?

 

Many possibilities but two come to mind...


1) Your mechanic is lieing to you or intentionally causing a fault for $$$ reasons

Or

2) Because Jaguar.

Your issue sounds like its electrical, has anyone just tried re-seating every single plug? My car has a few old OEM bosch type clip plugs which fail due to age, nothing like a bit of high temp silicone to reseat them properly. As for sitting yes the cars do not like to sit, I left mine for 4 weeks once and it sputtered for awhile before waking up.

Sometimes to it doesn't hurt to call another Jag shop the owner etc might of had the exact same issue and a light bulb will go off.

 

Quite easily. Loom wires have been moved, clips and connectors undone and done up, and 30 year old wires and insulation moved about, etc etc. Things get hot then cold then things that are just hanging on can fail.
It is a mistake with cars of this age to look for a golden bullet, the electrical systems are fragile all over unless carefully and methodically renewed. If the cam covers were off, things can fall into plugholes and stick on valves. You name it, it can happen. This is the reason owner-fixing rather than garage-fixing is really the only way to get an XJS reliable, short of a 85,000 UK pound professional rebuild.
In your place I would drive and enjoy it and wait for a more precise symptom to show its face!

 

Greg, Vancouver XJ6,

Thank you good people for your thoughts. Wife and I have decided to list the car for sale, which we just did this evening in the Jaguar Forums "Marketplace". We want to keep the car, but as I mentioned, we can't keep throwing money at it. As a last resort, I plan to have another dealer drive it before we let it go; hopefully he'll find something simple.

Thank you one and all who have offered suggestions and advise along the way.

 

:/ if I was anywhere within a day's drive I'd offer to go see for myself. If I haaad to guess I'd say injector and/or a spark plug issue... Simple really not worth tossing the car its not a dropped valve seat. Hopefully a second professional opinion can pinpoint the issue. As others said above..lots of old wiring can get disturbed one fault causing alot of pain.

 

Thanks for that thought, Vancouver XJ6, I wish it could be so. We're sick about selling it: I'm going to have one other jag authority look at it then make a final decision. Thanks again.

 

If you have a timing light I would connect that to each plug wire in turn. The light will flash if the plug is firing and it won't if the plug is dead. That's a simple and cheap test to see if the ignition side is ok, if it is then I would suspect wiring to an injector. The screwdriver tip listen test will help determine if the injectors are firing.

As a though, is there a high school with an auto shop class nearby. Sometimes they can do work on other peoples cars simply for the learning experience and have very reasonable rates. So far the tests suggests so far are nothing unique to Jaguar, they could be used on any car. Naturally if there is anything specialized that is unique to Jaguar I can guarantee someone here has done it before.

 

Jagboi64,

Thank you for the information and the high school auto class suggestion. I'll pass them along to my mechanic. He still has the car and is handling the sale. It's listed in the Member Marketplace.

Speaking of the mechanic, he's been in the business since before I met him and has maintained the car exclusively for over 20 years. He's also not charged me a dime in labor (only parts) since this vibration issue developed. He feels as badly about it as I do.

 

First, can you tell if it is a mechanical vibration verses a vibration induced from not all cylinders firing? If mechanical suspected, were all the belts removed so that none of the spinning accessories are rotating? For misfiring or a cylinder not firing, you can do what was suggested and pull each plug wire off to see if the miss remains. That would tell you that cylinder was not firing. Were these done?

 

Given that information about the mechanic, can I make a suggestion?

It can be really hard to diagnose or give tips since you don't have the car or the inclination to carry out tests. However, your mechanic is probably frustrated and would love to finally resolve the issue. If he sincerely wants to get this fixed, why not have him sign up here on the forum? There are people here who know more about the XJS than nearly anyone else in the world, and who are incredibly generous in sharing their expertise and wisdom.

If he started a new post or chimed in on this one, along with his more expert description of what he's tried so far, or can confirm as to the current state (all injectors firing, all spark plugs, etc.), it would be much easier for everyone here to narrow down the suspects and get you back in business. He might resist because I know some pros have low opinions regarding DIY forums, but I can guarantee you that there are people here who can help him. Just assure him it will be worth his time. What's he got to lose at this point?

I hate to tell you this, but you either aren't going to be able to sell it with the vibration or you're going take a bath on price and end up nearly giving it away. We would all like to help you and your mechanic get this resolved, because it will be the best outcome for both of you.

Cheers

 

If your mechanic has maintained this car for 20 years then I’m assuming he’s eliminated a single consistent miss or we’d be done by now.

I have no suggestion at all, but I’m eagerly awaiting the outcome. This all sounds too familiar. Other than the “vibration increases with rpm” bit.

is there any chance you shot a video of the engine exhibiting the condition?

 

carplanes, Mac Allan, JigJag

Thanks good people for hanging with me. You and the other thread participants are great and I appreciate your efforts.

So I drove the car about 9-10 days ago for the first time since the vibration began--- filled up the gas tank and washed it, To my surprise, I felt what seemed like a suspension or steering noise/movement, perhaps there was an engine vibration as well, not sure, I didn't focus on that because I was so surprised by the suspension? noise; Carsnplanes, that felt mechanical to me. I'll see the mechanic and the car hopefully the latter part of the coming week. Plan to ride with him and discuss it all.

Mac Allan, I did ask him about joining the conversation, but haven't received a reply. He may be reluctant as you suggested some would be.
JigJag, if there's a visible engine vibration, I will do a video.

Thank you all