Etude 1.6/ 2000 model. Tested the coils,ecu and both censors OK.still the car won't start . Is there any diagram for the ECU

As Anonymous said, Invest in a good quality workshop manual. There are even some websites out there, (Depending on the age and model of the vehicle), where you can get them online for free.

Test coil, ignition module, crank/cam sensors, ignition fuses, relays. ECU must get inputs from several places to allow spark.

there is no such model on this car.
this car has EFI, in 1992 , the 8 valve has TBI injection and the 16valve G16B had MPI (4 injectors)
both engines the ECU, creates spark at all times.
the input to the ECU is CMP /CKL cam and crank sensors
then the ECU computes ADVANCE and then drives the ignitor
next to the Ign coil. the coil charges and the ECU release this
charge and BAM , mr. Tesla inductive spark. hits the DIZZY.
that is how spark works.

the ECU controls fuel not spark , or better the ECU controls
spark INDEPENDENTLY from fuel;. (with exceptions)
exceptions:
or are you asking about the fuel safety feature built in to all EFI
cars 1988 too now? that is the ECU does monitor Spark
and CMP and CKP and does in fact cut fuel, when the ECU
sees spark missing, yes. It cuts the INJECTORS !

as does , wide open throttle cranking cuts fuel. (injection)
and fuse is (fuel pump) cut after 3 second key on, unless you crank it or runs.

see block diagram here.
http://www.fixkick.com/ECU/EFI.html

Considering the whole system runs with a common crank sensor, the first place I would test would have also been the coil. If these have been tested and are ok, I would start looking at the ecu. The signal to the coil is generated by the ecu and unless there is a break in wiring, it is more than likely the problem.

If you have access to a wiring diagram, check for the coil trigger signal from the ecu. If this is present at the ecu, problem is wiring. If no signal at ecu then that's your problem.

Keep in mind that cyl 1&4 and 2&3 fire together off common coils in the coil pack so the fact that those cylinders are faulty together, also leads to ecu.

I know the fiat's have a history of problems with ecu- especially if the vehicles are valet'd and the engine pressure cleaned.

Please give us feedback regarding what you find- hope I led u in the right direction!

check your source power make sure power is flowing to your coil check all fuses and breakers

Cranks ok, won't start.
no spark at coil. ! main HV terminal.
checked fuses, no. (that be FIRST)
scan the PCM/ECU, no. (call it ECU from now on)
hopeless lacking scanner but... ok we try,,,,
if the fear of scan tools is so bad, then you get to do it the hard long way. okay.

The ASD relay runs this show, (fuses MUST TEST GOOD)
rule 1, the ASD most close, at key on
the ECU closes the ASD for 2 seconds. to start engine.
if not the ECU sees errors (asd can drop cranked or running)
there are 1 to 8 errors, on this car less, but still many.
if throwing parts blind is good, then new ASD relay?
test 1:
turn key, hear the ASD click we use a stethoscope to hear it.
2 man test, due to 2 second rule.
it must click or its is bad, or lost power to ECU. (fuses) or other power feed issues to ECU. (key switch bad)
what we do , if our scan tool was stolen, (haha) we
measure all 4 ASD pins at the 2 second rule.(a voltmeter)
and the 4 voltages tell 4 things
ASD ok or not OK
or ECU never once turn it on, (more work, lacking scanner)
lots.

http://jeepdied.com/ASD.html

those are the ropes.
fixing cars lacking a scan tool, is like the most hard thing to do.
I can do it, but I have vast tools in my shop.
Even a voltage data logger.... to monitor all ECU pins.

The ECU is just logic, if the inputs are wrong so can outputs.'
GIGO it's called. Garbage in , Garage out.

Well, to start with, there are a whole lot of things (including a bad fuel pump) that can cause a cylinder misfire. A misfrire code does not mean that you automatically start replacing ignition coils.
The fuel pump is not supposed to have power to it any time the ignition switch is on. It will only have power for about 2 seconds to "prime" the injectors, then it will remain off until the engine starts and gets over 500 RPM.
Did you test any of the ignition coils to see if they were in working condition before you replaced them?
Did you test the ECU relay to see if it was functioning properly before you replaced it?
If the mechanic was able to scan the ECU and get codes ot of it, the ecu relay HAD TO be working at the time...WHY did you replace it?

ECU failures are extremely rare - especially on Nissans. However, poking around in the engine control circuits without knowing what you are poking on is a REAL GOOD way to GET an ECU failure!

I recommend that you read the following article and get back to me if you need further assistance:

What Else Could Be Wrong?

fuel rail preasure rgulator valve may be faulty

Sounds like a bad ECU module it controls fuel injection and spark.

The ECU have may have detected an error. A scanner would tell you the error code is to determine accurately the problem. If the gauge checks out OK, the car's computer may be faulty that it causes the shutdown early. If you know someone who has the same car and engine and try out the ECU on your car to check if it is not a ECU malfunction. If it is not the ECU it could be a blown head gasket or worn out. It could also be the ignition system, the sparks may not be firing when the temp increases on your engine. An ignition coil or distributor that is on its way to break down may nor work properly due to heat. You may want to have it tested either by observing the sparks or trying out another unit, a spare or a borrowed unit.