1976 280z engine runs rough then dies, will not idle.

[mbz]

Just now, Dave WM said:

hence the need for doing exactly the procedure as asked. Hang in there you will get it worked out, and it will be sweet when you do!

Yes I get it. And I appreciate the help.

I'm confident we'll get it sorted out soon enough.

Thank you!

[Dave WM]

any updates? inquiring minds would like to know.

[mbz]

Got the new battery in today, $110 at Costco for an Interstate Battery with 3 year warranty.

Will do other tests tomorrow.

Edited March 31, 2019 by mbz

[mbz]

OK Guys, here's the results, ALL of the readings below are with the NEW BATERY installed:

Checking the vacuum on the fuel pressure regulator (FPR) as it affects the fuel pressure while the engine is running.

0). New Battery Voltage Reading: Everything OFF = 12.48 Volts, Engine Running = 12.12 Volts

1). Fuel Pressure PUMP ONLY = 29 psi. (see photo 1) [This seems VERY ODD considering last test with old battery was 35.5 psi]

2). Fuel pressure reading while the engine is running = 41 psi (see photo 2) [PRESSURE UP]

3). Fuel Pressure with FPR Vac. line disconnected = 44.5 psi (see photo 3) [PRESSURE UP]

4). Fuel Pressure while Sucking on the vacuum hose from the FPR = 40 psi (see photo 4 & video) [PRESSURE DOWN]

5). Fuel Pressure while Blowing on the vacuum hose from the FPR = 44.5 psi (see photo 5) [PRESSURE UP / NC]

 

Edited March 31, 2019 by mbz

[Dave WM]

ew Battery Voltage Reading: Everything OFF = 12.48 Volts, Engine Running = 12.12 Volts

Lets deal with this 1st, so with the engine off Key off you get 12.48 at the battery terminal, but with the engine on and the motor running you get 12.12 volts at the battery terminals?

That would indicate a charging problem. Will get back to the fuel later but have to understand what is going on.

 

[Dave WM]

Next test will be to remove the return line from the fuel rail and have it dump directly into a empty container. The idea is to remove any possible restriction int the return line to the tank. Perform the engine running test again. Watch out for the gas coming out of the line, you will have to stop the engine before you over flow your catch basin.

 

[Dave WM]

I am not a believer in replacing parts unless you know for sure they are bad. Do you have a vacuum gauge? if so what does the vacuum read on the intake manifold while idling, use the same hose connection point you are using for the FPR.

 

[mbz]

16 minutes ago, Dave WM said:

ew Battery Voltage Reading: Everything OFF = 12.48 Volts, Engine Running = 12.12 Volts

Lets deal with this 1st, so with the engine off Key off you get 12.48 at the battery terminal, but with the engine on and the motor running you get 12.12 volts at the battery terminals?

That would indicate a charging problem. Will get back to the fuel later but have to understand what is going on.

Just re-tested this and got the following results:

Engine OFF / Key OFF = 12.52 volts

Engine ON / Motor Running = 12.70 - 13.00 volts (fluctuates)

[Dave WM]

ok thats better, now move on to the return line disconnected test. watch out for the gas, make sure you have it going into a secure container so as not to spill raw fuel all over.

[mbz]

15 minutes ago, Dave WM said:

Next test will be to remove the return line from the fuel rail and have it dump directly into a empty container.

 

11 minutes ago, Dave WM said:

Do you have a vacuum gauge? if so what does the vacuum read on the intake manifold while idling, use the same hose connection point you are using for the FPR.

Which test should I perform first?

I don't have a vacuum gauge but can have one in about 30 minutes.

[mbz]

Just now, Dave WM said:

ok thats better, now move on to the return line disconnected test. watch out for the gas, make sure you have it going into a secure container so as not to spill raw fuel all over

About how much gas should I expect to have to collect?

2 gallons?

5 gallons?

More?

[Dave WM]

I would start with the unrestricted fuel test, there has to be a reason for the high pressure, assuming the intake in a vacuum.