Loss of acceleration when hitting gas hard

[gotham22]

I own a 1978 280Z that runs well when I press the gas pedal smoothly. However, if I try to accelerate quickly or shift faster while pressing the pedal aggressively, it feels like the fuel flow cuts off. The RPMs remain steady, but the car loses power. If I ease off the pedal, the issue resolves. The car runs fine as long as I’m not too abrupt with the accelerator—it only happens when I press it quickly. Any ideas as to what is going on?  

[Zed Head]

Can't remember if you still have EFI or if you went to carbs.  They might have different causes.

[SteveJ]

It sounds like the car is going lean. Assuming you have the stock fuel injection, check the vacuum line going to the fuel pressure regulator. It may be rotten. If not, the FPR could be on the way out.

Having a fuel pressure gauge might give you good info.

[siteunseen]

You can run a gauge to your windshield wiper under a partially closed hood. Zip-tie the hose and gauge to the wiper and go for a ride. 

[zKars]

Change the fuel filter too. Sure feels like fuel delivery to me. Plugged lines, plugged filter, pump going bad.

Also check the dizzy hasn’t come loose or the vacuum hose to it hasn’t fallen off.

[gotham22]

Thanks.  It is stock fuel injection. I will try the suggestions 

[Yarb]

First step IMHO install a fuel pressure gauge between the filter and fuel rail. Inexpensive and will give you an idea real time of what’s going on.

[cgsheen1]

Remember that the FPR should maintain a 36.3 PSI difference (balance) between the fuel pressure and manifold pressure. Your manifold pressure (vacuum) is lower at idle and under low load so fuel pressure is that much lower than 36.3 PSI. (at 10 PSI of vacuum the FPR should be maintaining about 26.3 PSI on the fuel) At heavy load the manifold pressure decreases, so to balance, the fuel pressure increases. (so, at 1 or 2 PSI vacuum, the FPR should be keeping fuel pressure at 35.3 or 34.3 ish respectively)

Once you go to a positive manifold pressure (boost) the FPR should add that positive value to the fuel pressure. Ask me how I know. 🤭

This may not apply but it's always something to consider. A long time ago as an apprentice plumber I learned about fluid pressure and rate of flow. Two pipes: 1/8" and 1/2" - they can have the same fluid pressure applied, but the 1/2" pipe will always be able to deliver a higher volume of fluid. This may apply IF there is an unseen obstruction inside the fuel pipe or tubing. Pressure may read at an appropriate value but the system may not be able to deliver the volume needed at certain times. The pressure will only show a decrease when the demand outstrips the ability to supply. (this happened to me as my fuel supply hardline was over 1/2 plugged with corrosion inside at a point near the firewall - difficult to diagnose and pinpoint)

Edited November 29 by cgsheen1

[gotham22]

Good info thanks.  Going to get a gauge and report back to the thread 

[Zed Head]

Could be the throttle position switch.