Misfiring I think??

[CN280z]

1975 280z auto fuel injected

Misfire video??

Alright, my car was running into issues starting I just replaced my starter and now it’s starting up like a charm! However now I’m on to a new problem. when the car idles it sounds like is a little sputtery in the exhaust

 

but the main issue is the second there is load on the car under 25mph I’m hearing popping coming from the engine.
 

It sounds like maybe a misfire. I placed my hand in front of my air intake and I can feel it sucking in air until it pops then I can feel air push out. Then it goes back to sucking in air. the second I get over 25mph it stops. So I can drive at highway speeds or normal speeds around town. But if i come to a red light or a stop sign the pops start again under load while driving until 25mph then it stops again.

 

i just replaced the fuel filter and it seems to be running better over all but the popping is still there.
 

I replaced one fuel injector back in the day but I don’t know if this could be a possible problem. I pulled all of my distributor caps off and noticed each one caused a noticeable difference in performance so I don’t think it’s a bad spark plug.
 

So I’m at a loss atm and I don’t want to go spending 100’s replacing everything fuel related just to figure out I’m wrong lol.

[SteveJ]

What is the timing at idle and at 3,000 RPM?

Have you checked the valve lash?

[dutchzcarguy]

1 hour ago, SteveJ said:

What is the timing at idle and at 3,000 RPM?

Yeah.. what i thought.. can it be that your vacuum in the distributor is defect..

[frankachino]

I have the same issue with my Z right now. I discovered I had a vacuum leak at the manifold gasket. It idles fine, but the second I put load on it, it starts to sputter until higher RPM. Might check to see if any hoses have come off or are cracking. As dutchzcarguy said, it could be the vacuum advance in the distributor has gone bad.

[CN280z]

6 hours ago, SteveJ said:

What is the timing at idle and at 3,000 RPM?

Have you checked the valve lash?

I honestly have no clue how to check that or where to begin lol. I’m a very novice mechanic lol 

[Zed Head]

7 hours ago, CN280z said:

load on the car under 25mph I’m hearing popping coming from the engine.

It might be the typical "lean" problem with the EFI systems.  You can add resistance to the coolant temperature sensor circuit and fix it.  Link below.

It could also be clogged injectors.  When I got my car it had been sitting for a while.  The injectors were unbalanced, some were under-squirting by quite a bit.

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

Edited January 20, 2023 by Zed Head
+ be

[Zed Head]

Don't forget valve lash.  It's the very first thing mentioned in the tune-up chapter.  Very important.

[SteveJ]

26 minutes ago, CN280z said:

I honestly have no clue how to check that or where to begin lol. I’m a very novice mechanic lol 

Fair enough. We were all there at one time. Consider joining the Desert Z Association (http://www.desertzassociation.com/) and ask if someone could help you or recommend a shop. Another alternative is that maybe a member on here could help you or you could pay him to work on your car.

[Mark Maras]

You can find a tutorials on YouTube for specific projects like valve adjusting.