Fuel Delivery Problem???

[RoscoP]

I have a 1983 280zx Turbo. Is the fuel cap vented or non-vented? With the cap screwed down tight if I put it to the floor from a rolling stop, it runs great until it gets up to about 3000 rpms than it bogs/bucks. If I ease off the pedal when it starts doing this, it will take the fuel and run right up to speed. When it starts taking the fuel, I can put it to the floor and it will run right up with no hesitation and power as designed.

 

If I remove the fuel cap, it will run right up to speed without any hesitation at all rpms. BUT it doesn't seem to get up to speed as fast and doesn't seem to have the power when the cap is on and screwed down tight.

 

Any and all suggestions greatly appreciated~~~~RoscoP

[NewZed]

If it's not just your imagination, it seems like tank venting might be involved.  Not through the cap but through the charcoal canister and its vacuum lines and vent hoses.  It may be that it's not lack of fuel but overpressure.  Just a guess.  Maybe you're boosting the fuel tank.

 

The cap should have a little spring-loaded valve on the inside center.  Take a look.  You can pick it open with your fingernail.  It lets air in but none out.

[RoscoP]

Thank you for your quick response. Here are a couple of pictures of my gas cap. I don't see what you are referring to as far as a spring loaded valve that can be picked open with my fingernail.

[NewZed]

That's different than a 280Z's.  But that's what "vacuum relief valve" means on the diagram I attached.

 

If you have a mighty vac you could probably rig something up to see if the valve opens.  Or if no one is looking you could suck on it, procedure described in the attached picture.

 

By the way, all of these pictures come from the final few pages of the 1983 EFEC chapter.

 

[RoscoP]

Did the old suck test. I can suck it in and it makes a little noise. I don't know if that's good or not. Sooo............I guess I will purchase a new fuel cap. I'll try and locate an OEM cap. Thanks again for your quick response.

[RoscoP]

Here are a couple of pictures of a used cap off ebay for a 280zx Turbo. Looks just like mine. I'm going to take your first diagram with the vac hose routings and trace mine and see if I can find a problem before I purchase a new cap.

 

Thanks again for all your help. If I find the problem and fix it, I'll post again.

[RoscoP]

I think I found the problem. I printed out FSM Engine Fuel & Emission Control System.

 

A.  Carbon Canister Purge Control Valve checks out OK (does not leak) as it should.

 

B.  Carbon Canister Constant Purge Orifice does not leak as it should. It is supposed to leak!!!!

 

I used short spurts of 120 p.s.i. on the hose to free up the orifice (stated on page 126). Didn't work!!!

 

It says to remove Purge control Valve and check Constant Purge Orifice for leak.  How do I do that????

I don't see any way to separate to remove the cover.

 

I have included pictures from the FSM (pages 125-126).

 

All help and suggestions greatly appreciated.  Thank you~~~~~Rosco

 

[RoscoP]

I fixed it!!! At the suggestion of another "Z" owner, I disconnected all the hoses running to the charcoal canister. I plugged the 3 going to the engine and left the one coming from the fuel tank unplugged.

 

It runs perfect (idle, acceleration and etc) with the gas cap screwed down tight.

 

If and when I sell, the new owner can buy a canister that works properly. My canister had the small line going to the engine check valve froze up and would not breathe. The check valve is inside the canister according to the FSM.

 

This emission setup is the simple of the simplest to satisfy USA's new emission program in 1983. It is designed to put the fumes from the gas tank through the engine. You couldn't do what I did on today's emission controlled engine as they are very complicated and require big bucks to keep them to specification.

 

Thanks for all your help~~~~RoscoP