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

wont start when hot

Old 03-20-2011, 10:04 PM
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wont start when hot

after i drive my z around for awhile it won't start. it will crank but die. so far it has eventually started, and when it does it runs rough, huffing and chugging and will then throttle up when i press down on the accelerator. after revving the engine for a minute it runs smoothly.

i'm new to mechanics, sorry if this is dumb, but where and how do i start diagnosing this problem? it has only happened to me after i've driven it around (usually for about 20 minutes at least) and it has sat for less than 30 minutes or so. i have driven it for 45 minutes and let it sit for 2 hours and it starts up fine.

a man sitting next to me at the grocery store said something about a cold start problem, but i didn't catch everything he said. he said to turn the key to "on" but not to ignition several times and then try. 'too old to read the codes,' he said as he drove away.

i need a good mechanic in portland!
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Old 03-20-2011, 10:46 PM
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The next time you drive it, turn the ignition on and leave it on for a few seconds then hit the starter. Sounds the fuel rail isn't holding pressure.
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Old 03-21-2011, 06:38 PM
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thanks. i will try that.
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Old 03-24-2011, 11:02 AM
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hey you ever get a quote for me on the fender flares?
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Old 07-20-2011, 06:32 PM
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Originally Posted by anniversary_Z View Post
after i drive my z around for awhile it won't start. it will crank but die. so far it has eventually started, and when it does it runs rough, huffing and chugging and will then throttle up when i press down on the accelerator. after revving the engine for a minute it runs smoothly.

i'm new to mechanics, sorry if this is dumb, but where and how do i start diagnosing this problem? it has only happened to me after i've driven it around (usually for about 20 minutes at least) and it has sat for less than 30 minutes or so. i have driven it for 45 minutes and let it sit for 2 hours and it starts up fine.

a man sitting next to me at the grocery store said something about a cold start problem, but i didn't catch everything he said. he said to turn the key to "on" but not to ignition several times and then try. 'too old to read the codes,' he said as he drove away.

i need a good mechanic in portland!
First off, sorry to revive an old thread but its relevant.

I have the same problem with my Z. I'm not sure where to start looking. It has a new CHTS thats only a couple of months old so I don't believe it's that. The only thing that is different for me is, when I get my car to fire somewhat, it sounds like its firing on 4 of 6 cylinders until I bring the throttle up to 3.7k in which they all start working and its ready to go. It usually takes about 15 tries or so for it to catch on just the 4.

Any suggestions?

And the fuel rail is holding pressure, according to your test.
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Old 07-25-2011, 08:16 AM
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We had a similar issue when we completed our NA2T conversion. It turned out we need to use a different ECU. Has anyone been messing around with your ECU? Did this problem just start on it's own or was something changed on the car and than it began?

Keep in mind the CHTS, coolant temp, fuel temp, O2 sensor etc are only input to the ECU for fine tuning the mixture. You can unplug all of them and the engine will start and run well. The only thing the engine needs to run is the injectors and spark plugs to fire. If it is starting fine when cold than will not when it's hot? There's a idle up and cold start valve on the drivers side of the intake, you can pull the vacuum lines from it an plug them to see if that's where a vacuum leek is.
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Old 07-25-2011, 08:30 AM
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Well, I bought my Z over the winter and it never did it then. But now that summer is here, it started to do this. The odd thing is that it's not consistent. I have not "played around" with the ecu. Just small stuff like checking codes. But for all I know, this ecu may be the wrong one for this car.

Thanks for the reply
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Old 04-21-2016, 10:02 PM
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i fix it

Originally Posted by anniversary_Z View Post
after i drive my z around for awhile it won't start. it will crank but die. so far it has eventually started, and when it does it runs rough, huffing and chugging and will then throttle up when i press down on the accelerator. after revving the engine for a minute it runs smoothly.

i'm new to mechanics, sorry if this is dumb, but where and how do i start diagnosing this problem? it has only happened to me after i've driven it around (usually for about 20 minutes at least) and it has sat for less than 30 minutes or so. i have driven it for 45 minutes and let it sit for 2 hours and it starts up fine.

a man sitting next to me at the grocery store said something about a cold start problem, but i didn't catch everything he said. he said to turn the key to "on" but not to ignition several times and then try. 'too old to read the codes,' he said as he drove away.

i need a good mechanic in portland!
Did you ever figure it out i had the same proble and i just fix it
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