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Datsun 280zx wont start all of a sudden


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hello everyone and im sorry if this topic has been discussed before.

im restoring a 1983 datsun 280zx with a L28 (non turbo) engine and a few months ago i was finished with the engine resauration and tried starting it up and it started up right away and ran perfect! in the last few weeks the engine had been on a few times (to show my friend). but now this morning the engine does not want to start up at all , the engine goes around but wont start.

what is working / have i checked?

fuel? : tank is a quarter full and also the fuel rail has presure (fuel flies out when i take of the fuel line)

spark? : yes a strong spark with new spark plugs

when i try to start the car for a while there comes a lot of fuel out of the intake tube (intake filter box is off).

is the engine just flood or does anyone have any suggestions on what to check? 😬

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nothing has changed since a few weeks ago, i was super busy with school work. the CSV valve is the vaccuum valve on the intake right? (im dutch so i dont know all the names).

how do i check if it is stuck open? and how would this cause the engine to flood?

 

thanks for the response btw! Greatings

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the cold start valve is supposed to inject fuel when temps are low, its controlled by the thermo/time switch. Its fires only when its cold and only while the ign key is in the "start" position, and then it should only fire for no more that 9 seconds.

IF for some reason the Cold Start Valve (CSV) is stuck open, it will just shoot gas constantly into the intake manifold. You can try disabling it by pinching off the fuel line that goes to it. Be gentle with the hose connection, the CSV is plastic and being old you could break it. They are expensive.

Another source of excess fuel causing flooding (presuming this is the problem) is a break it the diaphragm of the fuel pressure regulator. the FPR has a vacuum line that connects to the intake manifold. Pull this and see if there is any raw gas leaking when trying to start, there should be NONE.

Lastly if an injector is stuck open you could have a leak from that. If I understand the issue you are having a leak closer to the mouth of the throttle body, that would point me towards checking the CSV since it is located near the entry to the intake manifold (more so than say the injectors).

You did not answer if the spark plugs are wet.

 

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o sorry! all the plugs are super wett. 

i havnt checked the CSV yet, next time i will disconnect the little fuel line going there and top it off to make sure the valve wont spit any more fuel in the intake. can i just drive without it? or is it really needed to ensure the car wil warm up/ start up better?

the FPR should be fine i think, the vacuum hose that is on there is dry, not even a single drop of fuel. also i get a really good (and clean) return

i also tought about the injectors but that should be a little weird because the fuel is comming out of the throttlebody. but ofcourse nothing is imposible and i could fill up the whole intake and then spit it out at the throttlebody.

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Yes indeed fuel comes out of the AFM. When i see the picture you just posted i think the CSV is open all the time. Also i dont think a injector can spray so much fuel in that it will come out of the AFM

Edited by TerrenceW
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The engine will take longer to start with the CSV plugged or removed.  But it's not too bad.

It's a simple device and might just be stuck open.  It's easy to test.  Removing the fuel line and plugging it is a simple and easy way to see if that is the problem.  Don't forget that it will have 36 psi behind it at all times with the pump on.  And you might leave your plugs out and spin the engine to blow the excess fuel out.  Sounds like there was a lot of excess fuel in the manifold.

Edited by Zed Head
Afraid of misspellings for some reason.
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okay so i had a few hours left today and i checked what would happen if i disconnected the CSV fuel line and then tried to start it. Its alive again!! thanks alot guys! 

i think the valve is indeed stuck open

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1 hour ago, TerrenceW said:

okay so i had a few hours left today and i checked what would happen if i disconnected the CSV fuel line and then tried to start it. Its alive again!! thanks alot guys! 

i think the valve is indeed stuck open

Yea!

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Now you can trouble shoot that, it could also be the thermotime switch, less likely as it tends to fail off, but easy to find out. try hooking up the CSV to a 12v source, use some clip leads to it and supply a 12v (unplug the csv from the wire harness, connect the 12 directly to the csv, never the harness) it should "click". if not its prob stuck, you maybe able to get some carb cleaner into it and try cycling it a lot with the outside source.  Not a bad idea to run some good fuel injector cleaner with your next tank full of gas.

I thought about it more, the thermotime ONLY gets 12v during the crank so even if it was stuck on, the only thing that would happen is the injector would fire regardless of temp and would fire as long as you held the ign in the "start" position. I don't think that would allow enough time for the flooding you are having. So pretty much has to be the injector.

Edited by Dave WM
gave it some more thought
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A lot of people delete the CSV for the problem it caused you. One less problem it seems. I live in a warm climate so it has no bearing on my 280. If I remember right it just knocks a couple of seconds off cranking anyway. You may have to turn it over twice without it? Overkill in the early EFI systems. The newer ECUs measure the ethanol content for cold start-up.

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7 hours ago, Dave WM said:

Now you can trouble shoot that, it could also be the thermotime switch, less likely as it tends to fail off, but easy to find out. try hooking up the CSV to a 12v source, use some clip leads to it and supply a 12v (unplug the csv from the wire harness, connect the 12 directly to the csv, never the harness) it should "click". if not its prob stuck, you maybe able to get some carb cleaner into it and try cycling it a lot with the outside source.  Not a bad idea to run some good fuel injector cleaner with your next tank full of gas.

I thought about it more, the thermotime ONLY gets 12v during the crank so even if it was stuck on, the only thing that would happen is the injector would fire regardless of temp and would fire as long as you held the ign in the "start" position. I don't think that would allow enough time for the flooding you are having. So pretty much has to be the injector.

Ahh okay, well then it is weird that the engine now runs perfect without the CSV.

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8 minutes ago, TerrenceW said:

Ahh okay, well then it is weird that the engine now runs perfect without the CSV.

what are your engine temps when starting? as mentioned its really only for cold climates, I presume your location is cold now. When the EFI is working right it pretty much starts in a fraction of a second. and you can drive right off. it works well when everything is perfect. I don't know if you car has an o2 sensor, if so it is a little smarter in that it can go into closed loop and try to compensate for problems with the fuel mix. the early ones (like my 75) work great as long as every sensor/injector is work properly. The is no feed back from an o2 sensor for the ECU to compensate with. Glad you got it working, if it works well without it then you have a simple fix. plug it. If it every starts being hard to start when its very cold, you can revisit this.

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4 minutes ago, Dave WM said:

what are your engine temps when starting? as mentioned its really only for cold climates, I presume your location is cold now. When the EFI is working right it pretty much starts in a fraction of a second. and you can drive right off. it works well when everything is perfect. I don't know if you car has an o2 sensor, if so it is a little smarter in that it can go into closed loop and try to compensate for problems with the fuel mix. the early ones (like my 75) work great as long as every sensor/injector is work properly. The is no feed back from an o2 sensor for the ECU to compensate with. Glad you got it working, if it works well without it then you have a simple fix. plug it. If it every starts being hard to start when its very cold, you can revisit this.

I live in holland so its only a few degrees outside right now. If the engine will start up hard i think i will get a new CSV but for now i will delete it. Also i dont have a O2 sensor. What type used the O2 sensors? I have a 1983 280zx 
also deleting stuff like this will make the engine look cleaner haha

Edited by TerrenceW
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I think that emissions efforts were driven by the States, mostly California, the LA basin, because we have so many cars and burn so much fuel.  Choking on the smog.  A 1983 European model 280ZX might not have an O2 sensor, or a catalytic converter.

Can't find a reference source but I'm also pretty sure that many non-States 280Z's still used carbs for quite a while after EFI was introduced.  

 

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1 minute ago, Zed Head said:

I think that emissions efforts were driven by the States, mostly California, the LA basin, because we have so many cars and burn so much fuel.  Choking on the smog.  A 1983 European model 280ZX might not have an O2 sensor, or a catalytic converter.

Can't find a reference source but I'm also pretty sure that many non-States 280Z's still used carbs for quite a while after EFI was introduced.  

 

I indeed have no O2 sensor and also no kat haha, just a straightpiped 6 cillinder. best sound ever!

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