I have AU2 factory duel fuel. Recently changed spark plugs/lead, running extremely well but started to back fire last week when stepping on accelerator whenever engine is left cold, noticeably in the morning, otherwise it's ok. Is this the problems gas mixture in the converter? Can someone please confirm or otherwise? Thanks.

Try camshaft position sensor i have same problem with mine 2000 grand cherokee 169k

Well, those are classic symptoms of bad engine timing, so I'd have that checked. Maybe your timing belt has jumped a tooth.

Be careful with that starter fluid, you could blow yourself up.

Any codes?

The next time it won't start ,pull a sparkplug wire and see if you're getting fire.Then we'll known whether its a ignition or fuel problem and go from there.

First you need to determine whether or not the fuel is getting to the cylinders. If it is, the problem has to do with the ignition side. Assuming that the engine has been running recently, Check for gas smell by removing a spark plug after cranking the engine. If there is no gas odor and the spark plug is not wet, there is a problem with the fuel delivery. Check that the fuel pump runs, you should hear it for a few seconds when the key is first turned on (it's in the fuel tank) just before the engine cranks. If the pump runs, check for pressure at the injector rail - you will need a service manual for some of this. If the fuel is getting to the cylinders, check the ignition coil by pulling one of the spark plug wires mostly off and listen for a distinct snaps as the engine is cranked. If this doesn't lead you to the problem, you'll need someone with proper test equipment to help you. It could be bad electronic ignition, bad cpu, broken wiring, battery low, short somewhere, bad switches, bad fuses, fuel pump shot, fuel filter plugged, out of time due to broken or slipped timing chain, etc. Extremely plugged air intake or exhaust could do it, too, but would more likely cause it to start and then shut-off.

When you replaced the fuel pump, did you notice if the pick-up line was in good condition or not? I have been told by a mechanic that has over 35 yearsof experience that this was a common problem, and especially now with Ethanol being mixed in with fuel.

Check the spark, remove the fuse to the fuel pump and remove one of the spark plugs. Connect the plug to its lead and position it well away from the engine against the truck frame (do not hold it) and turn the engine over, check the spark. If no spark it most probably a faulty coil. Check the impedance of the spark plug leads and replace any that are much higher than the rest. My guess is that you have spark but no fuel, What?... OK this is what I think is wrong. Your pump is fine when at position 2 on the ignition switch however when you switch to position three to fire the engine the power to the fuel pump is momentarily disconnected. A leaking fuel pressure regulator or injector would drop the pressure in the fuel line and at the same time flood the engine making it impossible to start. Once you start the engine with ether the ignition is back to position 2 and the pump can make good any loss in pressure but because the intake mix is rich this will cause the engine to run rich too. A good fuel system is capable of delivering 40 - 50PSI of fuel pressure and when switched off up to 90% of this pressure should be maintained for about 5 minutes, if it cannot check out the fuel pressure regulator and injectors. The fuel pipe should be capable of filling a pint pot in about 15 seconds, if it cannot check out the fuel filter is clogged.
Hope the above gives you some pointers

could be fuel pressur regulator or coils

You must have the plug leads in the wrong place on the distributor.
Firing order is 1-3-4-2
Remove the distributor cap. There is a tiny mark on the aluminum body where the cap sits on it. Turn the motor clockwise by hand until the rotor lines up with this mark. #1 plug lead should be in the distributor cap hole closest to the rotor in a clockwise direction.
If the motor still does not start rotate all the plug leads 180 Deg.

try putting fuel injector & carburetor cleaner that mite solve the problem