Datsun 280zx wont start all of a sudden

[TerrenceW]

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? 😬

[Dave WM]

are the plugs wet?

if you suspect flooding you may want to make sure the CSV is not stuck open.

so nothing was changed prior to the non start?

[TerrenceW]

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

[Dave WM]

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.

 

[TerrenceW]

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.

[Zed Head]

Fuel would be coming out of the AFM according to your description.  It's the next thing after the air filter.

[TerrenceW]

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 January 26, 2021 by TerrenceW

[Zed Head]

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 January 26, 2021 by Zed Head
Afraid of misspellings for some reason.

[TerrenceW]

okay thanks! i will try this tomorow when im in my garage. ill keep you updated

Edited January 26, 2021 by TerrenceW

[TerrenceW]

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

[Dave WM]

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!

[Dave WM]

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 January 26, 2021 by Dave WM
gave it some more thought