# 1986 Z31 wont stay running, help please



## JeremiahB (Aug 10, 2013)

Hey Z31 lovers, my name is Jeremiah and I have a 1986 Nissan 300zx. Recently I have been having some issues with it. My car won’t stay running. 

Detailed description of my problem:
When I start the car it will start fine then die within a few seconds. It dies in a “chocking” manner. If I give it gas I can keep it alive but as soon as I give up the gas it will die still.

Today I paid a bit more attention to the way it dies. I can give it gas and it responds but if I hold the accelerator down it won’t hold an RPM for long it will begin to choke If I pump the accelerator every few seconds the rpm will spike and stay alive as long as I keep pumping the gas. 

After prolonged periods of keeping it alive after I let the gas go sometimes it will hover below 500 RPM and try its hardest to stay alive but eventually dies. I have noticed my volt gauge moving around as this is happening also.

On my ECU I get code 31. Sometimes I get code 23. After erasing the computer and starting over code 31 pops up always after it dies and sometimes when I give it gas and try to save it at low RPM I can get it to display code 23.

Troubleshooting so far:

Firstly I replaced the fuel filter. Plugs and wires look ok. Battery is good. Fuel pump is fairly new (less than a year) I cant seem to find any vacuum leaks or exposed wires. I noticed my electrical connection to the fuel temperature regulator was off but I connected it back up. 

As far as code 23:
I have used the manual to diagnose code 23: 
I did a continuity test in pin 18 and 25 on the ECU input harness and the test passes for continuity / resistance when I depress the gas pedal and release it. The flow diagram says everything is fine and I can only get code 23 sometimes anyways.

For code 31
I have a spare ECU, swapped it out, no change. I am fairly confident that at least one ECU is working
Code 31 is about electrical load for the following systems AC/heater, power steering, radiator fan, head lamp, and rear defroster. I started taking out fuses to see if anything made a difference.

I removed 2 AIRCON blower, head lamp, and AIRCON control fuses and disconnected the heating control unit in the interior. I actually don’t have AC so the AIR CON fuses are a bit confusing but I was using a diagram from the web.

I was hoping someone can help me with this issue. My skill level is intermediate do it your self guy (mostly because I can’t afford otherwise so I make do) Everyone tells me to junk this car because it is old but I will never give up on it. Thanks a lot Z31 community

Jeremiah


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## i r teh noobz (Apr 26, 2007)

Its hard to say without seeing the car, but I'd try checking fuel pressure. It certainly sounds like a vacuum leak though. Did you check the air intake between the MAF and throttle? A can of brake cleaner can make finding leaks much easier - just keep it off of your paint.

Does it run fine as long as you hold the pedal off idle? If so, check the idle controls - perhaps the idle valves are clogged or sticking? 

Code 31 shouldn't really be causing an issue. 

My cars all showed the idle switch code sometimes, even when they ran fine. I wouldn't worry about the TPS unless your resistance readings are out of whack.



Ask on Z31performance.com. You will get more help there. Traffic is rather limited here, especially in this section.


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## JeremiahB (Aug 10, 2013)

i r teh noobz said:


> Its hard to say without seeing the car, but I'd try checking fuel pressure. It certainly sounds like a vacuum leak though. Did you check the air intake between the MAF and throttle? A can of brake cleaner can make finding leaks much easier - just keep it off of your paint.
> 
> Does it run fine as long as you hold the pedal off idle? If so, check the idle controls - perhaps the idle valves are clogged or sticking?
> 
> ...



I can’t seem to find any vacuum leaks or exposed wires. I specifically looked for vacuum leaks between the Mass Air Flow Sensor and the throttle body as recommended by some forums but I couldn’t seem to find any but I admit it is difficult using break cleaner to probe while it has a hard time to hold a constant RPM/idle. 

I did a fuel pressure test, hooking the gauge inline, after the fuel filter. I got approx.35 PSI (Key ON Engine OFF and Key ON Ignition ON). The working pressure should be 32 PSI so I think that eliminated fuel pump issues.


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## i r teh noobz (Apr 26, 2007)

Have you checked ignition timing and the timing belt?


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## BeyondBiscuits2 (Jan 18, 2006)

I had a very similar situation happen to my Z31 a few years ago. At first I thought it had jumped time, and ended up completely rebuilding the engine after being given bad and improper advice. Not that I'm upset about that, it needed it anyway after 175k+ miles of irregular maintenance and upkeep. Anyway, got everything put back together, and went to start it up. Engine ran nicely on starting fluid, but wouldn't idle or rev without sputtering and bogging on petrol. Anyway... long story short, turned out to be the MAF sensor. NEVER ONCE did my ECU throw a MAF code, but when I unhooked it, car idled like a dream. Plugged it back in, DEATH! I picked up a salvaged MAF, cleaned it up, slapped it in, car is back on the road successfully.

P.S. a simple test to determine MAF failure is to unhook the sensor, and start the car. Once it does start (it will be hesitant to do so), it should idle smoothly and without issue. You can even rev it without trouble to around 2000 rpms before it'll cut out. After you've done this and get the aforementioned result, plug the MAF back in and try and duplicate. If it persists with being naughty, that's your culprit. Sometimes even a Fairlady can be a b*tch .


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## JeremiahB (Aug 10, 2013)

Thanks man. I unplugged the MAF and it idles perfectly. Plug it back in and it dies for sure!. I tried to clean it with MAF cleaner but no good. It doenst help it. Anyways thanks a lot man!!


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## BeyondBiscuits2 (Jan 18, 2006)

Glad I could help. Always a good thing to use someone else's experiences, whether good or bad.


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## Brewen (May 3, 2014)

*Ignition Pickup coil*

Change the Piece inside your Distributor. Its called the electronic pickup coil. When it gets old and goes bad it will run for a few seconds then get hot like the regular coil then shut off. It is a little black round computer chip looking thing with a thin silvery disk inserted into it i such a manner that it rotates really fast and sends a signal to make the car fire. Ill leave you a link to the picture of it.

1986 Nissan 300ZX Distributor Ignition Pickup LX653
Click that link it will show the ignition Pickup coil. If anyone else has this problem LOOK AT THIS. IT happened to ME.


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