1977 280Z Stuttering

[Zed Head]

1 hour ago, BayAreaZ650 said:

The issues (bouncy idle while warming up the car and the Z intermittently bucks during acceleration) hasn’t gone away. I installed a fuel pressure gauge. During idle, I’m getting roughly 39 psi and with the key in the ignition on “on”, it’s at 0 psi. Yesterday, I cleaned the throttle body, afm connector and used rubber gasket to plug a small crack in the tube between the afm and throttle body.

 

On 2/19/2021 at 5:39 PM, BayAreaZ650 said:

I replaced all the fuel lines on the rail and the Z runs as it should! I just got back from a 20 minute drive. One of the rubber hoses had a pinhole leak and was squirting a decent amount of fuel. I appreciate everyone’s help!

What changed?  You said it ran right for 20 minutes.

Your fuel pressure reading is too high.  What happens to it if you remove the vacuum hose to the FPR?

[Dave WM]

A lot of issues can come from modification and air leaks. 1st has there been any mods to the EFI or any other engine system?  I dont recall a detail picture of the engine bay, it may help spot something out of the ordinary. 

as ZH mentioned your fuel pressure is too high for idle, that could be a FPR thing (defect or lack of vacuum), or a pluged return line, or a massive loss of vacuum, in which case the engine would run like poo.

as far as the 0 pressure that is the way the system works, the fuel pump only runs when the engine is cranking or running. if you just turn the key to "on" but the engine is not running the pump will stay off. Its to prevent fuel from feeding a fire incase of a malfunction. 

A simple smoke of the intake system will find leaks. also a vacuum reading would be good, you should see around 15-18 inHg on a warmed up engine at idle. Vacuum leaks show up most when idling. Smoke out the system and look for leaks. Its very easy get a cheap cigar, plug up the front of the AFM, blow smoke into the intake manifold thru the brake boost port (attach a rubber hose and blow smoke there). watch out for smoke. 

I am assuming the idle adjustment screw works and the rest of the system is intact. 

 

[zspert]

Folks, what I'm going to write is not meant as a criticism of anyone but an observation backed by 50 + years of experience. Car spent a very long time at the body shop and is a 280. ALL 280s, approaching 50 years old or so now, suffer from a partially or completely plugged internal gas tank filter.  The symptoms described fit the bill but let's prove it before we start throwing  money at the problem and hope it goes away. 

If a customer brings a 280 to me with performance problems and the cause isn't obvious the next step - ALWAYS the next step -   is to install my fuel pressure gauge between the fuel filter and the fuel rail. The first test is to see what the fuel pump, original pumps are still available from Nissan and God do I hate to see an aftermarket pump cobbled together with the reason given, "those Nissan pumps are too expensive",  is capable of. With the engine running I pinch off the return line. The pressure gauge should immediately go to about 55 psi. If at the same time the car starts to run much better then you can count on the in tank filter being at least partially plugged. If after pinching the return line the pressure doesn't increase markedly then the pump is shot.

Based on reading most of the posts it sounds like a classic partially plugged in tank filter.

I've seen lots of 280s that came out of storage , same as sitting a long while at a body shop, with partially calcified in tank filters.

[Zed Head]

On 2/23/2021 at 8:20 AM, BayAreaZ650 said:

I’m getting roughly 39 psi and with the key in the ignition on “on”, it’s at 0 psi. Yesterday, I cleaned the throttle body, afm connector and used rubber gasket to plug a small crack in the tube between the afm and throttle body.

 

On 2/18/2021 at 11:04 AM, Zed Head said:

Forgot to say - check your fuel pressure if you can.  Might be something simple like a failing fuel pump or a clogged filter.

Should show up on fuel pressure.  

[EuroDat]

I made an instruction back when I had pressure problems 6 years ago. I posted it in the tech section. It will help identify where a leak in the fuel system is. It might help.