I have an 86 n/a Z31 and it is hard to start in the first time of the day. It takes me around 10-15 seconds. Any other time after the first start it is fine. Cold weather makes it worse.
The fuel injectors, FPR, and fuel filter are new. The throttle body and MAF were cleaned. The fuel pressure checks out ok. The spark plugs and wires are new. I have a new air regulator as well. The vacuum is good, but the vac lines need to be replaced.

Any ideas anyone? My suspicions are with the fuel pump. Can a fuel pump be lazy until warmed up? Once the car is started up the acceleration is terrible for a few seconds. The Z kind of sputters and then it's almost like something finally clicks and it goes. Any and all help would be greatly appreciated.

 

From what I've been gathering (I just bought an 87 na with a similar issue) and a lot of posts point to the CHTS (Cylinder Head Temp Sensor) failing. Mine will turn over, and seems to dump fuel causing difficulty starting and idling until the engine warms up more. After warming up everything works much better. I have a sensor on order so I can't verify if it'll resolve the issue.

z31.com | Repairs | Changing the CHTS the Easy Way
Maxima Forums - View Single Post - Horrible gas mileage on my '87...

 

im having the same problem with my 84 50th ae, once warmed up, it will start right up everytime, but the first start takes awhile, then it sounds like its misfiring, and the idle is like 500, then jumps to 2000 for the 30 second lean surge with the ECU, but after that, it only settles down and idles at 1200, its still high, but runs perfect, im lost to, anything you find post it, and ill post whatever I find, ive been trying different things and will hopefully find out whats wrong.

 

fine once warm? = yes, bad CHTS. Replace with genuine Nissan, consider new subharness. The sensor has failed to provide values for the enrichment process durning a cold start.
http://www.z31.com/repairs/chts.shtml

 

I just changed the CHTS in my z this passed weekend and my hard start problem is still there. I do smell gas when I finally start it. I also checked the fuel line running underneath my z and this is a slight "ding/dent" in it. The fuel line is not crimped, but its not perfectly round either. Can the smelling of gas or the dent in my fuel lien have anything to do with my hard start problem?

 

I changed the ignition coil and the O2 sensor. No chnage from the O2 sensor. The iginition coil has shortened the hard start time, but the hard starting is still there.

My next project is to change the timing belt.