Jaguar Repair: series three jaguar wont start, mass air sensor, inner fender

Question
Hi My jaguar xj6 series three wont start. I got in one day , started it and put my seat belt on . Then it died. This was 10 months ago , it hasnt run since.  It has a good spark, i laid a plug wire on metal with a spare plug in it and turned the key, good spark.I used a rented noid light to check and found that the cold start inj lights when the key is turned but not the other injectors.My passenger side tank has a hole in it so i had been using the dr side for 4 years Fuel is pumping strongly up to the fuel rail. I have put on a new pressure regulator and all three relays on the firewall.My son has the same year 1984 jaguar so i took off his car the mass air sensor and put it on mine , no go , i also did the same with the aluminum box in the trunk behind the pass side rear seat. Ithink it is called a ecu, no go , the same with the small aluminum box under the air inlet on the inner fender on the pass side that supplies power to the injectors, no go . All of these items work fine when put back on my sons car.I drained the tank and put 5 gals fresh gas in along with a can of product that is supposed to absorb water.No go . I also replaced the black plastic box that plugs into the distributer and put on a new dist cap and wires and cleaned and gapped all the spark plugs. I also  changed the ign behind  where the key fits . There are some other things i have done but this is all i can remember at the moment. The battery was renewed also and there are a bunch of wires at the rear of the block that are ground wires. I cleaned them also.When i spray easy start into the air inlet it will start briefly then die.  . The car has 70,000 original miles on it. can you help, thanks John.

Answer
Hi John,

I learned when trying to diagnose a "no-run" condition to forget all symptoms and only look at systems. There are only 3 systems that make any engine run and they are,
Compression, Fire and Fuel. Any time a gasoline engine don't run, one or more of these 3 items is missing.

Every car that came to me in the dealerships I worked in that wouldn't start required that I run the exact same series of tests. Also, they MUST be done in an order.

Compression First. On a Jaguar you must see from 135 PSI to 165 PSI on every cylinder and they must not be much different from each other. The test must be done with the throttle open. If any cylinder don't pass this test, it is a waste of time continuing until it is corrected.

Fire is second. The fire (spark) must be thick (about as thick as a pencil lead) and be blue in color (not in bright sun light) The spark must be close to the correct time. (A rough test of this is easy by having all the plugs out and either have someone spin the engine for you or use a remote start switch connected between the white w/red tracer wire removed from the metal relay on the firewall and the positive post of the battery. While you hold your thumb over #1 plug hole. The compression will blow your thumb off of the hole with a "Pop". If you lay the plug of that cylinder with it's wire attached,on a metal part of the engine, you will see the spark which makes a "Click" sound. If the timing is close enough to start, it will seem as though the "Pop" is producing the "Click". However if you have a "Pop-Click" or a "Click-Pop" the timing is off and must be set. It then takes little to no time to test every cylinder the same way. Thus you have established that the timing is close to correct and the firing order is correct. Don't skip any cylinder.

Fuel is always last. This is easy to test too, but only if the first two tests are good. Take a spray can of starting fluid and spray into the intake while trying to start the engine. If it starts and will only run while spraying, then you do have a fuel problem. (There is an exception to this and this is a manifold vacuum test. connect a vacuum gauge to the intake vacuum (throttle closed) spin the engine and watch vacuum and continue to spin the engine and if vacuum drops down close to zero as you spin more. You have a stopped up exhaust system (Mufflers or CATs)

One or more of the three systems has to have failed for it to not start. These test will 100% pinpoint which system has failed. Once you have established which system has failed, let me know and I will give you a series of tests for that system.

Don't skip anything I have out lined. Then let me know.

Howard