Ran ok till i changed distributor,cap,crank sensor now it will not start codes up as safty shutdown,fuel pump relay circuit and ignition/distributer engine speed input circuit can anyone tell me whats the issue

Code 12 is a "good" code-it means system normal.
Since no codes are stored, check for spark and check for gas-is the fuel pump coming on? You should hear the pump buzz for a couple of seconds when you turn the key to on-it should start and pressurize the lines, then shut off until the engine is cranked-when cranking, pump should be running again. If you don't hear the pump, check if the fuel pump wire at the gas tank connector has power to it when the engine is cranking. If it does and the pump is not working, the pump will need replacing.
If no power, check the fuel pump fuse and relay, under the hood.
If the fuel pump is working, it may be ignition related-check for spark. You need to see a blue snapping spark to know the ignition system is good. If no spark, suspect the ignition control module or the crank position sensor -or the pickup coil, if no crank sensor. The pickup coil will be in the distributor-if you have one. If no distributor, crank position sensor is behind the crankshaft harmonic balancer.
If fuel pump and spark are good, you will need to diagnose the injector circuit.
Post back with what you find.

have the vehicle scanned while cranking to see if there is a crank position sensor signal (CKP). this tells the ECM that the engine is turning and timing for the spark plugs. If the Brain box doesn't know this then the ASD circuit is tripped and stops fuel and spark. relatives with a dynasty had a crank sensor wire severed from running over something and didn't mention it.

Check the fuel pump fuse and relay, if it's OK, you have a bad fuel pump. About the no spark, could be many things
Ignition coil, distributor (if so equipment) , main shaft position sensor, computer problem
Good Luck

pull one ignition cable out of cap just enough to see the tip of connector and crank it, a spark should jump from cap to tip of wire. no spark means you need the whole distributor replaced. buy it from nissan or infiniti dealer, it comes with cap rotor installed and 12 mo 12k mile warranty, no matter who installs it. dont waste time with aftermarket rebuilt distributor, those are not reliable. https://parts.infinitiusa.com/

If you hear that the engine cranks when you try to start the car then that is good. It means that the starter is working. If the starter cranks but the engine won't start, there could be wide range of problems. Here are some of the most common:
- Problems with fuel delivery system (e.g bad fuel pump, fuel pump relay, clogged fuel screen, etc.)
- Problem with engine electronics (e.g crank sensor, cam sensor, air flow sensor, power relay, engine computer, etc.)
- Ignition system problems, especially on older vehicles with the distributor (e.g bad ignition coil, commutator, rotor, distributor cap, etc.)
- Defective ignition switch
- Problems with vehicle security system
- Internal engine problems (e.g broken timing belt or gear, low compression, etc.)

Make sure you check the 3" intake hose from the air box to the intake manifold. May be cracked.

I worked on a '93 Quest last year. Couldn't find out why it wouldn't start. It was the distributor shaft not held onto its rotating gear. The roll pin had come out of the gear on the end of the distributor shaft. When the distributor cap was off, the rotor was turning with the shaft while the engine was cranking. So I thought that was okay. But when I put my finger on the rotor and it stopped turning, that is when I found out the problem. It's a stretch, but maybe the techs missed it. Take the cap off, and if you can spin the rotor either way just by hand, the distributor gear has come loose.

Looks like they really covered a lot. I suppose next they will you to replace the ecu. Good luck.

You can try to test the relay for function by swapping it with a known good working relay. If this does not work, you can put a jumper between the terminals that energize the pump (relay removed, ignition off). (On the Bosch Jetronic systems I used to work on, the pump would energize even with the ignition off). If there is still no sound, briefly turn the ignition on, and listen for the pump to energize. If you heard nothing, assume the pump is defective. I found most fuel pump problems and failures to occur in vehicles with 125,000 to 175,000 miles of use.

You may also try to check the Hall effect sensor ( a magnetic pulse detector that controls both spark and fuel flow) located within the distributor body (where the spark-plug wires attach to the distributor.

And finally, if that is good, check the ignition module within the distributor. It's a sealed transistorized circuit bolted to the inside of the distributor body with 5mm bolts.

if you have a 1.8-2.7- or 1.2 engine change the distributor cap and plugs and wires check timing also .it could be problems with the led photodiode in distributor. for the 2.2 and 3.3 it distributorless they have crank sensor and cam sensor. you will need a scanner to check those sensors. check to see which one of theses engines your vechicle have. go from there . your fuel pump relay should be in the engine compartment.

1 Inspect Battery Damaged or faulty battery and/or connections. here is a list of things u can check hope this helps Shaun 2 Inspect Coil - Ignition Damaged or faulty ignition coil or ignition coil circuit. 3 Inspect Fuel Filter Clogged or dirty fuel filter 4 Inspect Fuel Injector Pressure Regulator Faulty fuel injector pressure regulator or circuit. 5 Inspect Fuel Pump Improperly functioning fuel pump or circuits. 6 Inspect Wireset Damaged, worn, or deteriorating spark plug or coil wire(s). 7 Inspect Control Module-Ignition Faulty ignition control module or circuit. 8 Inspect Solenoid Switch Damaged or faulty solenoid switch or solenoid switch circuit. 9 Inspect Starter Damaged, worn, defective, or faulty starter or starter related circuit. 10 Inspect Neutral Safety Switch Damaged or faulty neutral safety swittch or circuit. 11 Inspect Fuse Corroded, burned, or shorted fuse may be interupting power source. 12 Inspect Fusible Link Corroded, burned, or shorted fusible link may be interupting power source. 13 Inspect Battery Cable Corroded, broken or poorly connected battery cable. 14 Inspect Spark Plug Wire Loom - Performance Improperly adjusted or worn/malfunctioning carburetor. 15 Inspect Distributor Cap Loose or cracked distributor cap 16 Inspect Distributor Cap And Rotor Kit Loose, cracked, or worn distributor cap and ignition rotor. 17 Inspect Fuel System Pressure Incorrect fuel pressure being delivered to carburetor or fuel injection system. 18 Inspect Fuel Injector Plugged, dirty or poorly connected fuel injector. 19 Inspect Ignition Switch Worn, damaged or faulty ignition switch or circuit. 20 Inspect Spark Plug Fouled, damaged or broken spark plug(s). 21 Inspect Belt Incorrectly routed, adjusted(tensioned), missing or worn drive belt(s). 22 Inspect Timing Belt Slipped or broken timing belt. 23 Inspect Timing Set Slipped timing chain or worn timing gear(s). 24 Inspect Fuel Tank Contaminated fuel from rusted or deteriorated fuel tank. 25 Inspect Ignition Timing Incorrectly adjusted engine timing.