300ZX (Z31) Forums Dedicated to 84-89 ZCars otherwize known as the Z31's

85' Z31 Lots of trouble starting when hot

Thread Tools
 
Search this Thread
 
Old Jan 2, 2016 | 05:26 PM
  #1  
KaiserVision's Avatar
Thread Starter
Registered User
 
Joined: Dec 2015
Posts: 7
From: West Palm Beach, FL
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.
Old Jan 2, 2016 | 09:29 PM
  #2  
NismoPick's Avatar
The Good Twin
 
Joined: Aug 2005
Posts: 20,639
From: Wild Wild West, UTAH!
Have you checked the ECU diagnostic codes?
Old Jan 3, 2016 | 09:23 AM
  #3  
86tcoupe's Avatar
Registered User
 
Joined: Nov 2013
Posts: 300
From: east KS
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 ?
Old Jan 3, 2016 | 09:24 AM
  #4  
rogerz's Avatar
Grumpy & Helpful
 
Joined: Sep 2006
Posts: 1,415
From: Mill Creek WA
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
Old Jan 14, 2016 | 08:42 AM
  #5  
KaiserVision's Avatar
Thread Starter
Registered User
 
Joined: Dec 2015
Posts: 7
From: West Palm Beach, FL
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?
Old Jan 14, 2016 | 10:58 AM
  #6  
NismoPick's Avatar
The Good Twin
 
Joined: Aug 2005
Posts: 20,639
From: Wild Wild West, UTAH!
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.
Old Feb 24, 2016 | 09:51 PM
  #7  
Mike Kwon's Avatar
Registered User
 
Joined: Jul 2015
Posts: 15
it seems like bad crank angle sensor....
Old Mar 22, 2017 | 09:08 PM
  #8  
tnewcamp's Avatar
Registered User
 
Joined: Feb 2013
Posts: 3
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.
Old Feb 1, 2020 | 08:20 AM
  #9  
Barneszy's Z's Avatar
Registered User
 
Joined: Jan 2020
Posts: 10
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.

Old Mar 6, 2020 | 01:58 PM
  #10  
rabidewok's Avatar
Registered User
 
Joined: Apr 2014
Posts: 4
Its going to be your fuel pressure regulator modulator
Old Aug 16, 2025 | 02:41 PM
  #11  
Xrandog's Avatar
Registered User
 
Joined: Aug 2025
Posts: 2
Two other possible causes.

Originally Posted by KaiserVision
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.
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.
Old Sep 22, 2025 | 08:57 AM
  #12  
Xrandog's Avatar
Registered User
 
Joined: Aug 2025
Posts: 2
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

Power ignition transistor w/heat sinks
Power ignition transistor w/heat sinks


Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
macanic
300ZX (Z31) Forums
1
Feb 1, 2020 07:39 AM
mcge8241
300ZX (Z31) Forums
4
Jun 18, 2019 02:47 PM
Defender405
300ZX (Z31) Performance / Technical
0
Oct 13, 2016 10:03 AM
vgterian94
300ZX (Z31) Forums
3
Jul 29, 2014 07:58 PM
Abeck85
300ZX (Z31) Forums
4
Jun 7, 2014 07:54 AM




All times are GMT -7. The time now is 08:00 PM.