Jaguar Repair: 87 XJS V12 quit running, fuel pressure gauge, bright sun light

Question
QUESTION: My 87 XJS (Hess & Eisenhardt) convertible just died while driving it. Now when I let the car sit for a day or two it will start and run for a couple of seconds and then die like it has run out of gas. If I try to start it again it won't fire at all. If wait a couple of days it again will run for a couple of seconds.

I did pull out the pump and main relay and tapped them and re-insert them with no change.

Thanks

ANSWER: Hi Irving,

When any engine dies it has lost one or more of the only three items necessary to run. Compression, Fire or fuel. They also must be tested in that order. However, it is unlikely compression as it will not usually return if it goes bad so You can move on to testing "Fire" (ignition)

It is a waste of time testing ignition when the engine will run. You MUST test it in it's failed mode (dead) If it does not stay dead long enough to test then there is a easy method to test it as it dies. Just take a timing light and tape the trigger down and connect the timing light up and run the wires out form under the hood and put the timing light under a wiper arm so you can see it flash while you drive. If you do this in bright sun light you can tape a piece of cardboard over the end of the light on the windshield so you can see the flash even in the bright sun light.

If the timing light goes out while the engine is still spinning down, you for sure have an ignition problem and further tests are necessary.

If you maintain a flash all the way to a stop then you have a fuel problem and you will at that point need a fuel pressure gauge and an extra piece of fuel line and a "T" connection to place just before the fuel rail. Be sure to put clamps on all the connections and place the fuel gauge under a wiper arm like you did the ignition test. You must see 28 to 30 PSI at all times. If the fuel pressure drops just before the engine dies you have a fuel supply problem and further tests are necessary.

Let me know which you have and I will give you more tests.

Howard

---------- FOLLOW-UP ----------

QUESTION: Howard,

Thanks for your quick response and great suggestions.I won't be able to further test the car for a couple of weeks as I will be traveling visiting kids.

The car is not driveable as it only runs for a few (5-10)seconds when it does start then dies and won't fire again for a day or two. Using a timing light and fuel pressure gauge were great ideas can't wait to tried it when I return home.

Thanks
Irving

Answer
Another quick test is when it won't start spray starting fluid into both intakes to try to start it that way and if you can keep it running with starting fluid sprayed into the intakes, then you know it is not ignition and you can go after fuel. Fuel supply first as I outlined. spray cans of starting fluid are available at most any auto parts stores.

Howard