78 runs very rough with no power when accelerating

[druiven280z]

Hi everyone.
Hope your all well.
78 - 280:
Wondering if anyone has gone through this issue. The engine starts and idles but not steady. Slight surging going on. Adjusting idle screw has no effect. Moving the flap in the air flow meter (Fractionally) causes better and incresed idle speed but further depression of the flap causes enging to stumble. Depressing the accelerator at the throttle body makes engine really stumble and hesitate. I have gone through the check list in the 280Z injection manual as well as the Engine Fuel section of the service manual. All checks resolve as OK however the manual I have is for 75-77. There are differences in the 78 but for the most part this manual can be used. Is there a specific fuel injection manual for the 78? I have gone through to find vacuum leaks and have not found any. The timing has been adjusted to 10 degrees before tdc as req’d. I have tried 2 different air flow meters and 2 different control units. Nothing seems to make a difference. I really can’t think of anything else to do although I have a feeling, I’m missing the obvious. I have a short video but I don't think we can upload videos to this page
Any help or suggestions would be greatly appreciated.
Cheers, les

[Noll]

Hmm, sounds like a vacuum leak of some sort to me - if the idle screw has no effect then air is getting into the intake beyond it, and trying to accelerate causing stumbling also points to that - ecu doesn't know the true amount of air going into the engine and isn't adding the right amount of gas when you try to accelerate. I don't have any experience with the specifics of the stock 280z efi setup, but that's a pretty universal issue when a vacuum leak is happening.

I'm sure someone else can chime in with likely culprits to look at; in the meantime it might be worth spraying some starter fluid around the various connections etc and seeing if the engine revs up - you've found where air is getting in if it does.

[druiven280z]

Hi everyone
Thought I would post the results of my findings.
Firstly all the signs exhibited pointed to a vacuum leak. However there was no Vacuum leak. The problem was a combination of faulty injectors, spark plugs and fuel pump. The injectors were the main source of the problem. Once they got sorted and I put in a new fuel pump and spark plugs along with a new fuel pressure regulator, the car runs great.
Cheers, everyone.
Ps Thanks for your post Noll.