I replaced the ecu in my car because it would not start at all. After doing this I had a bad misfire but then it just stopped starting again,within 2 days. My jag tech said my coils were the problem.So I put a spark tester between each coil pac and the plug and got spark at every coil. I tried removing the air filter and sprayed some fuel into the air duct while my buddy turned her over. This seemed to allow the engine to run but only on 4 cyls.To keep it running ,I must feather the gas.What does the fuel injection computer do and do you think this may be the issue or could it be just plugged injectors and how can I tell? I have some seafoam to try in the tank but wanted to hear from you guys before taking my beloved jag out anf flogging her on the highway.

 

My opinion is to get back to bare bone basics.

Lots of things come to mind, and I list a few, in NO particular order.

Refit the proper ECU, I have never heard of one "just dying", EVER.

SINCE YOU WILL BE MESSING WITH FUEL PLEASE BE BLOODY CAREFUL.

Confirm fuel at the injector rail. A very "simple" way is to prime the system (turn the ignition ON/OFF 3 times, go to the fuel hose connector at the rear of the fuel rail, and "CRACK" the 2 nut connection, and IF you get a "squirt" of fuel, pressure/flow will be assumed. IF you get no squirt, but just a "dribble", then NO fuel pressure or flow will be deemed. Obviously a fuel pressure gauge is the ultimate, but if no got one, this method will suffice to establish a running engine. NO FUEL, may be a blocked filter, or a dead fuel pump, both of these items are service replacement items, the fuel filter every 2 years??, and the fuel pumps usually "die" at about 100k miles??. If you got fuel, then the injectors firing (or lack of) and spark are the other 2 items on the test list.

Spark you seem to have established, HOWEVER, the coils on these engines are now starting to become a real PAIN, so a new/newish set will do NO harm at all.

The crank angle sensor at the front of the engine is another item that just goes "legs up" at about 100k miles, and NO reason why. It "sounds" like yours is OK, coz you got spark.

The camsensor, that thingy located at the front RH side of the engine where a distributor used to live, controls the sequential firing of the injectors, is another item that can cause issues. IF, and I say IF it has been removed at any time it may be refitted "wrongly timed", and the Nippon Denso ECU can work out the firing order of the injectors eventually, BUT it does require some serious cranking to do so. If in doubt recheck its timing, which I can explain if you need.

The coolant temp sensor in the thermostat base is another sensor required for starting and running, and it, and/or its wiring could be sending flaky signals to the ECU, and it then being confused, does nothing.

In the RH fuse box under the bonnet/hood, is a BLUE relay. This is one of the Ignition relays on these cars, and it can go bad, and then NO ignition power supply. Again, it sounds like you got ignition power, just listing as I think of things.

Get your "buddy" in the boot/trunk and see if he can "hear" the fuel pump "whirring" each time your turn the ignition ON, this will confirm if the pump is actually working.

Unplug the MAF, and establish teh terminals are clean and NOT corroded.

Clean the throttle body and disc, as they get a build up of "black gunk", and this caused all sorts of starting issues.

Your market has an EGR system, we DONT, so I have NO IDEA about that stuff, but I do read it causes all sorts of wierd stuff.

Report back, and we will keep an eye on the thread and answer as soon as possible based on what you tell us with the diagnosis.