Nissan Repair: 1991 300ZX running on 4 cylinders, import computer, c side

Question
QUESTION: Hey Calvin. Thanks in advance for any assistance you can give. I also am a volunteer on here under the A/C side of the house, so I know what it is like going out of your way to help others on here.
OK, I have a '91 300ZX 2+2, with the VG30DE (non-turbo) motor. My issue is that the 2 cylinders closest to the firewall do not seem to be firing. (One on each side) I have replaced the ignition module, verified the coils to be good by placing them into the known good cylinders, and have replaced the spark plugs. When I check the plugs they are wet with fuel, that leads me to believe that they for some reason are not receiving the signals necessary for the coil to spark. I have ran wire to wire continuity checks through the coil harnesses to the ignition module and the wires all check out as good, none are shorting to ground. That led me to the ignition module. Being as I do not know how to check this component, I simply replaced it, to no avail.
What am I missing? I am fairly mechanically inclined, have ran through the routes I know, I have also taken to my "mechanic" who is anything but a nissan expert.
I have a couple possible ideas, but would like to hear what your opinion is before I throw them out there so as to not hinder your thought processes. Also to validate my thoughts.
Background.... I replaced the timing belt not too long ago, due to me snapping the water pump housing neck in half (was getting on it a bit harder than I should have) However, it seems to me that it was doing this before I replaced the belt. Would the belt being a notch out of time cause this? If so... could you explain that to me, just so I have a better understanding. (my forte' lies with muscle cars, the whole purpose of me buying this car was to learn a bit more about import - computer controlled engines)

Thanks again, I look forward to your response.

ANSWER: Hi Dave -

Ah yes, muscle cars. I remember them - bout 30 years ago -

Anyway, your issue. I have a couple questions -

Do you have any check engine light on?

I am assuming the engine is missing? Or, does it not start? If it starts does it miss at idle, or once it reaches higher RPM's, does the miss clear?

Have you checked the injectors?

There is also a chance that the CPU is not providing proper input, so it could also be the computer.

Hope this helps - get back to me -

aloha
calvin


---------- FOLLOW-UP ----------

QUESTION: Thanks for the quick Reply Calvin. In response to your questions...
No, the check engine light is not on, and never has come on.
It starts fine (most of the time, I'll explain) and though I know it is missing on 2 cylinders, it runs somewhat smoothly. As though the missing cylinders perfectly balance each other out. Creating alot of the hood when it is propped open, but looking and feeling the engine itself, it doesn't shake like you would expect. It used to clear up and run perfect at higher RPMs (like it had to blow carbon out of the cylinders) but no longer does that. It misses throughout the RPM range now. As for the starting... If it has not run for a period of time, it starts smoothly, perfect, every time. (but misses during the starting) However occasionally, if I run it around and shut it off,... wait 5 minutes or so... try to start it again it will crank and crank but not start. Eventually it does start, after I find the perfect spot for the gas pedal, as though it is starving for fuel or even flooding. That has me lost also being that it is fuel injected and not carbeurated.
As for the injectors... I want to say that they are firing due to the plugs being wet with the fuel. But I have not pressure tested them, checked the o-rings to see if they are leaking, none of that. The car has 250,000 miles on it, and being that I bought it at 200,000 (really good price) I have to assume that they are the original injectors.
In fact, that was my next step I had considered is just replacing all of the injectors. I figured even if it wasnt the issue, it sure wouldnt hurt.
I hope this bit more helps you. Please let me know if there is anything more information wise I can give you. Thanks again.

Answer
Hi Dave -

Thanks for the info. Looks like the problem is fuel related.Actually my next suggestion was to check the injectors. Oddly, it is obviously firing, however if the needle valves are blocked or partially blocked in some way, then you will have too much fuel leading into your cylinders, causing the issue. If the plugs are black, that means too much fuel, or too rich. Too lean plugs have a white color electrode. Proper burning leaves a brown color. Also, makes sense that the car has a hard time starting after about 5 minutes - perhaps too much fuel has collected in the cylinder and car is hard starting (flooded), whereas if you wait a while, fuel has a chance to evaporate, and consequently starts with no problem.

It is also possible to be a faulty fuel regulator. Have the pressure checked both at the fuel pump and after the regulator at the rail. If there is not enough fuel pressure, the needle valves could not be closing all the way, also causing flooding, and, of course poor engine performance.

Of course all this is just speculation, and I hope you understand that it is really difficult for one to diagnose without physically being there, I wish I could be to assist you.

I think you are on the right track, though -

Let me know what happens -
aloha
calvin