General:

I have owned two v12 1988 xjs Hess &  Eisenhardt convertibles since 1997, and belonged to the Rocky Mountain Jaguar Club. until recently. Only 2000 vehicles of this model exist (1986 to 1988), mostly sold in the US, prior to jaguar introducing their own convertible design in 1988. A picture of one of my Hess &  Eisenhardt convertibles "pusycat" is shown below:

My favorite Pusycat - Jaguar Show Colorado Springs Sept 99

Hess Convertible

The jaguar XJ-S Convertible by Hess & Eisenhardt was announced at the New Jersey headquarters on Oct 29th 1986, and became available on special order thru US Jaguar dealers. Hess & Eisenhardt, based in Cincinnati, Ohio and founded in 1876, was rated as America's leading coachbuilders and had long built convertibles for Cadillac.

The interior of a standard saloon was stripped, the body placed in a jig, and steel structural members were welded to the sills. New panels were welded in before the top part of the car was repainted, blending in with the untouched bottom half.

The fully electrically operated top was designed to fold deeply into the body where, concealed under the color coordinated cover, it would disturb the cars smooth lines minimally (see picture of my car below, much sleeker than the standard production car). However this meant exchanging the single fuel tank for two, creating yet another leak prone connection and the need for two fuel pumps. The lower pump feeds fuel to the upper tank, and the upper tank pump feeds fuel to the engine.

Notice how the hood folds completely level with trunk body. Very sleek, regular XJ-s convertible owners have to suffer the large bump at the rear!

Hess Fuel System [The basics]

Mechanically this car is IDENTICAL to an 88 XJ-s coupe. Rumor has a habit of propagating propaganda, I hear so many untruths about how many design problems this car was inflicted, primarily the fuel vent system. I have carried out many repairs and modifications to this car, and I can categorically state, that 98% of what I fix is standard equipment on all HE XJ-s models. refer to my repairs and modifications page and see for yourself. The power roof has excellent reliability and is probably better quality than the early XJ-s Jaguar convertible models. 

After much studying and testing of the fuel system on my Hess & Eisenhardt I have come to the conclusion that neither Jaguar or any Dealership ever truly fixed the fuel system problems. The primary design flaw is the poor fuel vent system (common to the regular saloon, but does not have the added complexity of two fuel tanks!!). The vent system allows the fuel tank to gain too much fuel pressure when the engine is not running, spewing  fuel vapor into the air, trunk, or passenger at the weakest joint. Yes Jaguar had a recall (My car was fixed ha ha), but the vent system still allows the tank to gain too much pressure, and in my case the vent system was plumed wrongly creating a sealed and pressurized vessel. A very dangerous situation in a hot climate due to the expansion of the vapor in the tank.

A good basic test is to let the car stand in the sun for a relatively long period of time on a warm or hot day with the engine not running. Open the fuel filler cap and you will get one of the following (more information can be found at the fuel problem link):

(1) A large whoosh with the possibility of a crumpling sound from the tank. This       indicates the tank is building up too much pressure. Dangerous, fix this fault quickly. In the meantime disconnect the fuel tank vent pipe at the carbon canister connection to relieve the stress. Technically this is illegal in the US, but is a better solution than rupturing the tank. Don't park your car in the garage with the vent pipe disconnected, fuel vapor leaks out of this connection!

(2) A small whoosh indicates the tank vent system may be OK, fuel vapor could still be leaking.

(3) No whoosh indicates the owner probably has a leak in the tank or fuel vent system.

So in summary if you hear a bunch of old wives tales about this car, its a bunch of hogwash. You can use these old wives tales to your advantage and get a great convertible jag for a very reasonable price, of course only two thousand were made, and probably a good number of those are already on the scrap heap. 

I pity the poor owners that don't fix their own cars, they probably spent thousands at the dealership trying fix the never ending fuel smells, to no avail because the basic vent design is flawed. Of course only my opinion, but I am a rocket scientist and I should be able to figure out a simple fuel tank vent system after a series of tests. In conclusion if you want a real fix the owner must modify the already modified vent system. I am still working on the final version to the fuel vent system.

I am creating a registry of people who own XJ-s Hess &  Eisenhardt convertibles to set up some sort of correspondence system in order to help the owners with tech tips and general information. If you wish to register go to my XJs Hess &  Eisenhardt registry page.