Why did my Jaguar XJS just quit, or run badly on one side?

Short answer: When an XJS quits or runs badly, check the simple things before the scary ones: corroded relays and connectors, the fuel filter and the fuel pump. If one bank of injectors is stuck open, trace the wiring for a short before buying a computer. Run-on after shut-off can be a bad ignition switch or dieseling from carbon. And with a V12 this old, any fuel smell is urgent: NHTSA lists several fuel rail and hose leak recalls.

Symptom: The engine dies at a stop like it ran out of gas, runs rich on one side, keeps running after the key is off, or keeps setting a check engine message.

What to check first

1. Smell for fuel under the hood. Any leak means stop and fix it first.
2. Pull, clean and reseat the fuel pump and injection relays.
3. Replace the fuel filter if its age is unknown, and listen for the pump at key-on.
4. Read the code (the 1994 display shows a number) before buying sensors.
5. Get a repair manual with wiring diagrams for your year.

Likely causes

1. Corroded relays and connections. Jaguar owners say dirty relay contacts are a common cause of no-start, cut-outs and odd warning lights. Relays are electric switches that run the fuel pump and other parts.
2. Fuel filter or fuel pump. If the engine just dies like it's out of gas, the filter and pump are the cheap first checks.
3. Engine computer (ECU) or injector wiring. The computer opens each injector by grounding it. If a whole bank stays open, look for a shorted wire before replacing the ECU.
4. Dieseling (run-on) from carbon or exhaust leaks. Dieseling is when a hot engine keeps running after the key is off. Members blamed carbon buildup and a big exhaust leak.

What it usually costs

Owners in these threads didn't post prices.

Is it safe to keep driving?

Quitting at a stop is a crash risk in traffic. A fuel leak on a hot V12 is a fire risk; don't drive it if you smell fuel.

DIY or shop?

Relays, filters and wiring checks are DIY with a manual. ECU and fuel-injection work suits a Jaguar specialist.

Recalls, bulletins and complaints in plain words

• Related recalls: NHTSA lists several fuel leak recalls: 81V134000, 83V135000 and 85V087000 (1980-1985 fuel rail and high-pressure hose connections), 78V060000 and 78V063000 (1976-1978 fuel pipes and hose joints), and 92V009000 (1989-1991: the coil lead can sit near an injector hose and cause it to crack). Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect.
• NHTSA complaints: 38 keyword-matched complaints for Jaguar XJS / XJ-S 1976–1996 (of 82 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-30; keywords: stall, fuel, relay, dies, fire) (NHTSA returned no data for 42 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In My '94 Jaguar XJS cv just quit when I was at a stop light - on Car Talk, a '94 XJS convertible quit at a stoplight as if out of gas with a full tank, and had to be towed. Members said it could be the fuel filter, the pump, or electrical. A Jaguar owner said relays tend to corrode and can mimic serious problems like cranking but not starting.
• In 84 jaguar xjs v12 fuel injectors stay open on Car Talk, an '84 XJS V12 had the injectors on one side staying open all the time. Members explained the ECU opens injectors by grounding them, so check that bank's wiring for shorts before buying an ECU, and to buy a repair manual.
• In Jaguar 1988, XJS VI2 - CAR RUNS AFTER KEY PULLED on Car Talk, a 1988 XJS V12 kept running after the key was pulled. Members said a bad ignition switch could do it, or dieseling from carbon or an exhaust leak, and suggested a fuel-system cleaner before anything drastic.
• In Jaguar XJS check engine light keeps coming on on Car Talk, a 1994 XJS convertible with 121,000 miles kept getting a check engine message even after new oxygen sensors. Members asked for the code first.

Quick tip

On an old Jag, clean contacts fix more problems than new parts. Do the relays and grounds first, with the manual open.

Vehicle focus: Jaguar XJS / XJ-S coupe and convertible, 1976-1996, mostly V12.

Safety / mechanic note

Stalling and fuel leaks are safety items. Verify with a mechanic.