Fuel Pressure Help!

Faceman89

Faceman89

Member
Recently acquired a 1989 Corvette. I’ve got a head scratcher of an issue I can’t figure out. Car holds 35psi of pressure at the rail when running. Pressure drops fast when key is turned off. This was an issue when I bought the car. I have replaced the pump, filter, injectors with Bosch III units, rebuilt the fuel rail and replaced the diaphragm. When priming the rail with the return line clamped the pressure holds at exactly 40psi and doesn’t drop. I believe I have narrowed it down to the Fuel Pressure Regulator housing. Has anyone seen one go bad? I even swapped back in the old diaphragm out of curiosity and it also did the same thing. I’m at a loss trying to diagnose this. Any help would be greatly appreciated.
 
yeah, fuel pressure regulators on the C4 corvette FREQUENTLY go bad!
its well worth the time and effort to buy an ADJUSTABLE EFI fuel pressure regulator
if you block the return line and pressure remains constant but it drops when the return lines opened,
that eliminates the injectors leaking and fuel pump leaking,
leaving the fuel pressure regulator as the most likely failed part.

replacing a c-4 fuel pump

IF YOUR LOOKING TO JUST REPLACE A DEFECTIVE PUMP ILL OUTLINE THE BASIC STEPS YEAH I KNOW YOU WANT TO SKIP OVER AND IGNORE THE SUB LINKS... THAT WOULD BE A MISTAKE!! https://garage.grumpysperformance.com/index.php?threads/my-current-corvettes-383-combo.430/...
garage.grumpysperformance.com

fuel pressure regulators

Volume vs. Pressure FUEL Volume and FUEL pressure are two completely different things when you talk about fuel,supplied to an engine, but they must work together to give you the proper air/fuel mixture delivery. Both carburetors and EFI systems require the proper fuel volume to make the desired...
garage.grumpysperformance.com
 
I ordered a
Grumpy said:
yeah, fuel pressure regulators on the C4 corvette FREQUENTLY go bad!
its well worth the time and effort to buy an ADJUSTABLE EFI fuel pressure regulator
if you block the return line and pressure remains constant but it drops when the return lines opened,
that eliminates the injectors leaking and fuel pump leaking,
leaving the fuel pressure regulator as the most likely failed part.

replacing a c-4 fuel pump

IF YOUR LOOKING TO JUST REPLACE A DEFECTIVE PUMP ILL OUTLINE THE BASIC STEPS YEAH I KNOW YOU WANT TO SKIP OVER AND IGNORE THE SUB LINKS... THAT WOULD BE A MISTAKE!! https://garage.grumpysperformance.com/index.php?threads/my-current-corvettes-383-combo.430/...
garage.grumpysperformance.com

fuel pressure regulators

Volume vs. Pressure FUEL Volume and FUEL pressure are two completely different things when you talk about fuel,supplied to an engine, but they must work together to give you the proper air/fuel mixture delivery. Both carburetors and EFI systems require the proper fuel volume to make the desired...
garage.grumpysperformance.com
Click to expand...
Grumpy said:
yeah, fuel pressure regulators on the C4 corvette FREQUENTLY go bad!
its well worth the time and effort to buy an ADJUSTABLE EFI fuel pressure regulator
if you block the return line and pressure remains constant but it drops when the return lines opened,
that eliminates the injectors leaking and fuel pump leaking,
leaving the fuel pressure regulator as the most likely failed part.

replacing a c-4 fuel pump

IF YOUR LOOKING TO JUST REPLACE A DEFECTIVE PUMP ILL OUTLINE THE BASIC STEPS YEAH I KNOW YOU WANT TO SKIP OVER AND IGNORE THE SUB LINKS... THAT WOULD BE A MISTAKE!! https://garage.grumpysperformance.com/index.php?threads/my-current-corvettes-383-combo.430/...
garage.grumpysperformance.com

fuel pressure regulators

Volume vs. Pressure FUEL Volume and FUEL pressure are two completely different things when you talk about fuel,supplied to an engine, but they must work together to give you the proper air/fuel mixture delivery. Both carburetors and EFI systems require the proper fuel volume to make the desired...
garage.grumpysperformance.com
Click to expand...
I ordered an adjustable FPR and new diaphragm. Could it be possible that two diaphragms in a row could be bad? Have you ever seen the FPR housing go bad? I can only assume the seat that sits against the wobbly part of the diaphragm is possibly bad and letting fuel bypass it.
 
yeah, diaphragms leak, or can be incorrectly installed rather easily:like::crying::swearing:
 
NOT REALLY, JUST BE VERY CAREFUL the diaphragm is not ripped , mis-aligned or pinched excessively
 
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