Jaguar Repair: 86 XJSC engine cuts off after 2 seconds., fuel pressure gauge, manifold vacuum

Question
QUESTION: Hey Howard,
I have an 86 XJSC euro 3.8 5 speed.  The car was running choppy but runiing last week.  I came out the next day and it would not run.  The car starts for 2 seconds and then dies as though it is starting on cold start only.  I have good compression on all 6 cylinders, I have good spark, I have good fuel pressure mid to high 30's, and I pulled the rail and checked for injector spray, and I have good clean injector spray.  This goes against everything I know about motor cars.  Spark, compression, fire, should spell vroom.  Thanks in advance for any help you might be able to offer.

ANSWER: Hi Jason,
Did you do all the testing at the exact time of cut off? Did it have 30+ PSI when it died? Did you have a timing light on it at the time it died? Can you rev it up in that first 2 seconds?

Put your timing light on the coil wire not a plug wire and hold the trigger down and see if it flashes all the way down to the last revolution. Put the fuel pressure gauge on with a "T" fitting so you can see the pressure at the exact time of cut off.

It is unlikely a compression problem as compression will not usually come and go.

Try to spray some starting fluid in the intake to see if you can keep it running when it starts.

It would also be good to know what the intake manifold vacuum is. A stopped up exhaust can do that too. If the vacuum goes down before the engine dies that is the cause. leave the throttle closed to do the test.

let me know,
Howard

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

QUESTION: Hey Howard,
All testing has been done while trying to start the car.  Fuel press remains, timing light test indicates full spark until it stops rotating.  Engine will run on ether, but not on its own fuel, which before you ask is completely fresh.  The entire fuel system has been drained and cleaned. Vacuum appears to be fine.It will not rev on its own gas the two seconds that it will start.  Let me know your thoughts.
Thanks,
Jason

Answer
Since it runs on spray fuel it is for sure injection so you need to put a noid light on a injection plug and see if it flashes (which it will not) then check the power to the injector and if you have power then you need a wiring diagram of the injection system to confirm Ignition pulse signal to the ECU and check for ECU power supply and grounds as they usually have several.
If all that checks ok, then you need to find and try a known good ECU. Don't forget to test for a good connection between the ECU and each injector plug.
Howard