85' Z31 Lots of trouble starting when hot
 

I know there was an old thread for this issue, but I didn't think it would be ok to revive a thread from 2010. Anyways with that being said.

1985 300Zx Non Turbo

My car starts perfectly fine when cold, but after driving around and shutting the car off, within I would say about 2 minutes or longer of it sitting, the engine has a very very hard time starting. This issue has been apparent since I have bought the car, so it's not something that came up after a recent service or anything.

Recently I have installed all new parts for the cooling system, new timing belt, new battery, new starter etc.

The car will only run rough when starting hot, it will attempt to start, but chokes out after a few seconds, after revving the engine to about 3700 RPM once it finally tries to start, it sounds like it's not running on all cylinders.

It feels like it's starving for fuel, but i'm not 100% sure. it's driving me crazy.

Have you checked the ECU diagnostic codes?

Thats called Hot soak condition
Does your ride have the blower and duct work to the injectors ? Got it full of coolant ,radiator cooling good ?

try unplugging the O2 sensor. if the problem goes away - bad sensor. Another heat related item would be the chts being faulty. Read the fsm free download from Xenon

I ordered the CHTS it should be here by the end of the week, hopefully once that is replaced this issue will be fixed. I've done a lot of research and still cannot understand why the CHTS would cause an issue like this, but apparently a lot of people claim this is the root cause.

Can anyone back that statement up? or has anyone heard of that before?

Did you read / heed all of the above suggestions?
CHTS = Cylinder Head Temperature Sensor. Read all about it in the free FSM: Index of /FSM/300zx/1985

It's faster and cheaper to do tests, rather than throw parts at it. :)

it seems like bad crank angle sensor....

85 turbo no hot start after 10 min. The problem with my z was rusty gas tank the fine rust goes right through the filter and does not let injectors close lets fuel seep into engine and is flooded use of full throttle when starting will help a fix would be seal inside of tank with a ebay sold tank sealer or a quick fix would be a neodymium magnet on your fuel filter i used a 2in by 1/2in magnet. the metal fuel filter with magnet stuck on it will catch most of the rust but not all it was a big help for me.

I bought an 85 NA that had a similar issue. It would take 4-5 turn overs to start on a cold start. Ran fine until I would shut it down and restart after a brief stop (ie, getting gas). After the restart it would have low power, almost like the engine was bogging down. Wasnt running clean. After driving down the road a for a bit it would start to clear up. I took the car to Nissan (sales manager a good friend of mine) to replace plugs and just check for any other issues since I bought the car. He recommended that I replace plugs, wires, cap etc with OEM parts and so I did. Car starts on first kick now during a cold start, has more power and runs perfect after restart.

Two other possible causes.
 

84-86 Z31 2 + 0 there's a hot start assist module part #A18-800 100 obviously to mask a problem with the no start issue(and others). Also, the power ignition transistor part #22 020-12P11 can open up when overheating. Nissan corrected these issues starting in 87. Only pace you can find these are online or junkyard. Not saying that's the problem, but after spending $1,100, found out I could have done it myself for @ @$200.

Troubleshooting no hot start issue
 

1985 Base. Check the power ignition transistor(oem# 22020-12P11). Quick step to verify that is the problem: Take an ice pack and place on the part (located on the driver side strut tower under hood) for 5 minutes. Remove. Try to start. If starts, bad unit. Put the factory fix of a prw-2 unit with a crossover wiring and heat sink. Godzilla Raceworks has a kit for @$130.00. The other possible part failure is the hot start assist module(oem#A18-800 100). It is located under the battery tray(Nissan hid it because they knew of the hot start problem). I put heat sinks on my failing power transistor and didn't have a no start issue. So, after having the Cylinder head temperature sensor replaced with an aftermarket wet sensor, crank angle sensor in new distributor, complete tune-up wires, plugs, rotor, cap, fuel filter for the outrageous price of almost $1,500, my problem was the P.I.T. and/or hot start module, which I replaced for less than $200. After 2 weeks of driving at different distances without being able to replicate the no start issue, I deemed the problem repair. I did switch over to the PRW-2 w/heat sink conversion and replaced the hot start assist module. Picked up acceleration(like I needed more) and smoother idle and throttle. You all can send me some consulting $$...lol! Check the pic for heat sinks on power ignition transistor

PRW-2 link: Pallnet PRW-2 Igniter and Heat Sink Kit — Godzilla Raceworks

https://cimg6.ibsrv.net/gimg/www.zdr...8c41bc9522.jpg
Power ignition transistor w/heat sinks