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Is there a systematic way that I can use to find out why my fuel presure in a 78 280Z goes down in about one second after I turn off the engine? I tried putting straight Vise Grips WHILE having another person turn off the key. Presure still went down fast. I put the Vise GRIPS AFTER THE FUEL FILTER. Fuel gauge is installed in-line after the fuel filter. I have to CRANK AND CRANK TO START THE ENGINE, so I installed this 100lb. gauge and was I surprised to see the presure going down SO FAST. Norm K. PS: If I have to I will remove all the injectors. Please let me know. My car RUNS well.
 

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It depends on where the fuel pressure guage was in the scenario you describe. You don't specify if the guage was before or after where you clamped the line off. It was AFTER the vice grips (fuel filter, then vice grips, then guage), then your leakdown is somewhere in the engine. If it was BEFORE the vicegrips (fuel filter, guage, vice grips), that would indicate a problem in the pump or pump damper. You've already started the systematic approach. You just have to interpret what you're finding out correctly.
 

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Just two more things...

OOPS! Two more things. I did clamp off the cold start valve but it didn't make any difference. Also I did place the vice grips BEFORE the fuel presure gauge.....so it's leaking into the engine? I guess that sounds right. Norm K.
 

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Re: Just two more things...

If you ran the engine, clamped off the fuel line between the fuel filter and guage (filter, vice grips, guage) and the guage read a rapid decline in pressure, then yes, your problem is somewhere beyond the artificial blockage (the vice grips), which means somewhere in the motor. Just to make sure, do the same test but put the vice grips PAST the guage (filter, guage, vice grips). Theoretically, the system should hold pressure this way.

Fuel leakage in engine could be injectors. In fact, off the top of my head, I can't think of anything else it could be unless there's a big puddle under the car. (And you've already tested the cold start inj.) Might you be able to isolate each injector with your vice grips test? In other words, clamp off individual injector hoses, stop the car and watch your guage. If it's just one, the leak down should not occur with that one clamped off. BTW, speaking of a systematic approach, tracing down loss of fuel pressure (and just about everything else) is covered well in the factory service manual for your car. It's worth the $$ and time to search for one.
 

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is there gas in the oil? it might be just making its way back to the tank.
 

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???

Put the vice grips after the filter, and AFTER the gauge, BEFORE the fuel rail on the engine.

If the pressure holds, your check valve on the pump or relief valve is leaking back. The fuel dampener will not matter one way or the other, unless it's externally leaking, and that would be obvious.

Then move the vice grips to the RETURN LINE, and clamp it, and watch what your fuel pressure does:
If it goes up, to around 60-100 psi, then your pump is flowing properly...


But if you clamp between the filter, then the gauge, the onbly thing you will see is bleed down caused by one of the following items: Leaking injectors, or leaking fuel pressure regulator.

Those are the only two left.

If you have to crank and crank and crank to get fuel pressure up, see what happens when you clamp the RETURN line when initially trying to fire it. If the pressure comes up immediately, the FPR may be weak, and bypassing excessively. If it still takes a while to build, chances are the FPR is fine, but that your check valve is leaking (or a combination of both pump check valve seepage and fpr seepage)...

One way to keep from cranking so much, is to install a toggle to disable the starter "S" terminal while you hold the key in the "crank" position, so the pump will run and prime the bled-down system before you release the toggle, and let the starter engage.
Trying to start an engine with low fuel pressure is a beyotch...

Good Luck.
 
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