Jaguar Repair: 1984 xj6 series 3, air fuel ratio, combustion chamber

Question
My 84 xj6 will start and run for a second or two and die.  Alot of the relays have been replaced and the ecu has also been replaced.  THe fuel pump and all plumbing between tanks and pump is also new any suggestions on what to check now? thank you

Answer
Hi Josh,
All engines only require 3 items to run (with conditions on each)

1.Compression --- 135 PSI to 165 PSI with little difference between cylinders. Compression usually does not go and come back so you can forget compression for now.

2.Fire --- (Spark) Spark must be strong and at the correct time. Spark can come and go so it must be tested at the time of failure.

3.Fuel --- (Gasoline) must be available to each combustion chamber in an atomized form and in roughly the correct air/fuel ratio. This too can come and go so it must be tested at the time of failure.

It does not take a lot of high tech equipment to test for a loss of "Fire" or "Fuel". A timing light and a spray can of starting fluid from any auto parts store.

First put a timing light on any plug wire and try to start the engine and watch the flash of the light to see if the flash stops before the crankshaft stops when it dies. If the flash continues until the crankshaft stops then it is not ignition causing it to stop. If the light stops and the crankshaft coasts to a stop then it is ignition.

After you have established that it is not ignition, spray a shot of starter fluid into the intake after some one starts the engine and see if you can keep it running by spraying into the intake. If you can keep the engine running with the spray can, then "Fuel" is your problem.

These tests only tell you what section has failed not exactly what failed. Once you know for sure what section has failed let me know and I will give you a series of tests of that section (Fire or Fuel).

Howard