1991 Jaguar XJS Jag stalling out

MIKE PARTIN

MEMBER
1991 JAGUAR XJS
V12
2WD
AUTOMATIC
16,000 MILES

I have a 91 jag xjs. Vehicle stalls after running for a few minutes. Acts like its running out of gas. I have replaced the crank sensor and the fuel filter. Still has this problem. I checked the fuel pressure by removing the return line on the drivers side. It went to 80 psi. I looked up the specs and should be between 36 and 46 psi. But the engine boggs down and will die if you continue to throttle. I am a long time tech of GM and Chrysler. (24 years) It really acts like its running out of fuel. What am I doing wrong?

2 Replies

DAVE H

MECHANIC
13,383 POSTS

Repalce fuel pressure regulator. XJS
The fuel pressure regulator maintains constant fuel pressure in direct proportion to intake manifold vacuum. This is accomplished by attaching a vacuum diaphragm to the regulator.
When the ignition is switched to the ON position (engine not cranking), fuel pump is activated for 2 seconds (to raise pressure in the fuel rail) then shuts off. Fuel pump is reactivated when engine starts cranking.
Fuel pump operation is controlled by the ECU. If an injector malfunctions and the ignition switch is on, system limits fuel pump operation to prevent flooding.

The metering of fuel is controlled by regulating the injectors' opening time during each engine cycle. The frequency of the injectors depends on engine speed and conditions.
The basic injector pulse width is mapped against speed and intake manifold pressure. Manifold pressure is monitored by a manifold pressure sensor, located in the ECU, and connected to intake manifold by vacuum hose. Crankshaft sensor monitors engine speed and sends information to the ECU. The injectors of both cylinder banks are pulsed twice per engine cycle.
In addition to any necessary enrichment of air/fuel ratio according to coolant temperature, fuel injection duration is also increased by ECU during engine cranking. The increase in injection time reduces partially after cranking stops, and returns to normal injection duration after a few seconds. This helps keep the engine running during start-up.