Fuel Pressure Maintenance For The 1992 Corvette

The 1992 Corvette is a powerful car with a range of 300 to 375 horsepower and a 0-60 time of between 4.3 and 5.3 seconds. However, some users have reported issues with fuel pressure in this model of Corvette. CorvetteForum user Eddie4694229 reported that their 1992 Corvette loses fuel pressure and is very difficult to start, even after replacing the fuel pump, regulator, and injectors.

MotorTrend also published an article in 2013 about fuel pressure problems in the 1991 Chevy Corvette, which may be applicable to the 1992 model as well. The article suggests checking for issues with the fuel-pressure regulator, fuel injectors, oil-pressure sending unit, and other components.

Corvette Central's C4 Fuel Injection Overview page mentions that fuel pressure in the 1992 Corvette should be 32-38 PSI with the vacuum hose connected and 42-48 PSI with the vacuum hose disconnected.

Therefore, it appears that the fuel pressure in a 1992 Corvette should be in the range of 32-48 PSI, depending on whether the vacuum hose is connected or not. However, there may be other factors at play that could affect fuel pressure, and it is recommended to consult a certified Corvette technician if you are experiencing issues with your vehicle.

Fuel pressure gauge

A fuel pressure gauge is an important tool for diagnosing fuel system issues in a 1992 Corvette. It can help determine if there is a problem with the fuel pump, fuel filter, fuel pressure regulator, or fuel injectors.

To use a fuel pressure gauge, attach it to the Schrader valve on the passenger-side fuel rail. When the key is turned to the "Run" position, the fuel pump will activate for two seconds, pressurizing the fuel rails. On a 1992 Corvette, the fuel pressure should be between 40 and 42 psi at this point. If the pressure is lower than expected, it could indicate a problem with the fuel pump or a restriction in the fuel filter.

If the initial fuel pressure is within the normal range, the next step is to start the engine. With the engine running, the fuel pressure should jump to 38-40 psi. If the pressure is still low, it could be a sign of a faulty fuel pump or a leaking fuel pressure regulator.

To test for a leaking fuel pressure regulator, a fuel pressure gauge can be used to pressurize the system. Turn the key off and note the time it takes for the fuel pressure to drop by 20 psi. If it takes longer than 20 minutes, there is likely an issue with the fuel pump check valve, fuel pressure regulator, or a leaking fuel injector.

Further testing can be done by clamping the rubber portion of the supply line closed and then noting the time it takes for a 20 psi drop in fuel pressure. If it takes longer than the previous measurement, it confirms a faulty fuel pump check valve. If the times are similar, try clamping the return line instead of the supply line. If the time is considerably longer, it indicates a faulty fuel pressure regulator. If the time is less than 20 minutes, it suggests leaking fuel injectors.

In addition to using a fuel pressure gauge, other tests can be performed to check for leaking fuel injectors. One method is to raise the fuel rail slightly and place a piece of paper under each injector. After pressurizing the system, turn the key off and wait for about 10 minutes. If there are fuel stains on the paper, it confirms a leaking injector. Another way to test for leaking injectors is to listen for an injector's click (or its absence).

By following these steps and using a fuel pressure gauge, you can effectively diagnose and troubleshoot fuel system issues in a 1992 Corvette.

Fuel pump

The fuel pump is a vital component of the fuel injection system, delivering pressurised fuel to the injectors. The pump is located within the fuel tank and is cooled by the fuel that flows through it.

The fuel pump is controlled by the Engine Control Module (ECM) or the Powertrain Control Module (PCM). It is designed to deliver a constant fuel pressure, regardless of the pressure or vacuum in the intake manifold. This is achieved by releasing fuel back to the tank via the fuel pressure regulator. The regulator's return flow corresponds inversely to the pressure in the intake manifold.

As manifold pressure increases, the regulator returns less fuel to the tank. As manifold pressure decreases, the regulator returns more. The engine rarely uses all the fuel that is pumped.

At low coolant temperatures, wide-open throttle, high load and high rpm, the engine burns almost all the fuel that the pump delivers. At high coolant temperatures, idle and no load, the fuel pressure regulator returns most of the fuel back to the tank.

The fuel pump is prone to overheating if the fuel filter becomes restricted. This is because there will be less volume passing through the pump, which could cause it to overheat and fail. Therefore, it is important to regularly change the fuel filter.

If you suspect a problem with your fuel pump, it is recommended that you consult a certified Corvette technician.

Fuel filter

The fuel filter in a 1992 Corvette is located on the right-hand frame rail. Corvette owners are advised to change the fuel filter every year.

Changing the fuel filter on a 1992 Corvette can be a challenging task. The filter is located in a tight space, and accessing it requires removing several parts, including the fuel lines and the fuel pump fuse. It is also important to relieve fuel pressure and remove the fuel cap before attempting to change the filter. Some Corvette owners have reported completing the task themselves, while others have opted to have it done by a mechanic or service station.

One Corvette owner shared a detailed process for changing the fuel filter:

> "Starve engine by running it with the FP fuse out. Relieve fuel pressure at the rail; remove the fuel cap. Remove fuel lines from the fuel rail. Remove the fuel line bracket from the firewall. Remove the bracket holding the fuel filter. Disconnect the fuel filter towards the rear. Grab the fuel lines from the engine compartment and pull the filter out with the lines attached. Remove the filter from the fuel line. Reverse the process to install the new filter."

Another Corvette owner suggested a slightly different approach:

> "Run the car out of gas. Get the appropriate-sized wrenches (I think a 16 and a 13mm, but I'm not positive). Crack the fitting loose at the bottom or inlet side. Careful when you remove the line in case any residual gas is still in there. Then, for the front or outlet side, remove the right wheel well and from there, you can see the top of the filter. Have someone hold a wrench on the fitting while you, from under the car, spin the filter off. Put the new filter in place, tighten up the top fitting first, then connect and tighten the bottom fitting, replace the wheel well, and you're done."

It is important to follow safety protocols when changing the fuel filter, as gasoline can be dangerous and flammable. Some Corvette owners have reported getting gasoline on their hands and clothes during the process. It is recommended to wear gloves and protective gear to avoid injury and exposure to gasoline.

Symptoms of a faulty fuel filter in a 1992 Corvette may include difficulty starting the engine, especially after the vehicle has been sitting for a prolonged period. A restricted fuel filter can also cause the fuel pump to overheat and fail due to reduced fuel volume passing through it.

Fuel-pressure regulator

The fuel pressure regulator is a crucial component of a car's fuel system, ensuring the engine receives the appropriate amount of fuel. A faulty fuel pressure regulator can cause significant issues, including a rich fuel mixture, flooding, and even raw fuel being drawn into the intake.

Symptoms of a Faulty Fuel Pressure Regulator:

A faulty fuel pressure regulator in a 1992 Corvette can manifest in several ways. One common issue is difficulty starting the engine when cold, requiring the use of starting fluid. Once started, the car may run perfectly until it is turned off again. This could be due to a rich fuel mixture or flooding caused by a leaking fuel pressure regulator.

Testing the Fuel Pressure Regulator:

To diagnose a faulty fuel pressure regulator, several tests can be performed. Firstly, a fuel pressure gauge can be installed on the Schrader valve on the passenger-side fuel rail. With the key turned to the "Run" position, the fuel pump will activate, pressurizing the fuel rails, and the gauge should read between 40 and 42 psi. If there is no fuel pressure, check the fuses. If the fuses are intact, the next step is to access the fuel pump, which can be done by removing the cover under the gas door lid.

Further Diagnostics:

If the pump does not activate, tap on it while someone cranks the engine. If the vehicle starts, the pump is faulty and needs replacement. If it doesn't start, check for battery voltage and ground at the fuel pump using a Digital Volt Ohm Meter (DVOM). If voltage and ground are present, the pump is faulty; if not, check the fuel pump relay.

Checking for Leaks:

To check for a leaking fuel pressure regulator, perform the following steps:

• Install the fuel pressure gauge and pressurize the system.
• Turn the key off and note the time it takes for a pressure drop of 20 psi.
• If it takes longer than 20 minutes, you likely have a faulty fuel pump check valve, pressure regulator, or leaking injector.
• To pinpoint the issue, pressurize the system again and clamp the rubber portion of the supply line closed using clamping pliers.
• Note the time for a 20 psi pressure drop; if it takes longer, the fuel pump check valve is faulty.
• If the times are similar, pressurize the system and clamp the return line.
• Again, note the time for a 20 psi pressure drop; if it's considerably longer, the pressure regulator is likely faulty.
• If the time is less than 20 minutes, suspect leaking injectors.

Replacement Options:

If the fuel pressure regulator is indeed faulty, it will need to be replaced. Several options are available for the 1992 Chevrolet Corvette, including:

• AC Delco GM Original Equipment Series Fuel Pressure Regulator
• Delphi Fuel Pressure Regulator
• Standard Fuel Pressure Regulator
• BBK Performance Replacement Series Fuel Pressure Regulator
• Holley Die Cast EFI Fuel Pressure Regulator

These replacement options offer OE replacement or performance-oriented solutions to ensure your Corvette's fuel system functions optimally.

Fuel injectors

There have been many types of fuel injectors. The majority now work when an electromagnetic coil lifts a ferrous pintle or needle off its seat so fuel can squeeze through to the nozzle’s aperture and into the intake air channel. In 1989, GM introduced their own fuel injector. These are Multec fuel injectors. The Multec injector uses a ball to close off fuel flow and the injectors are raised up out of the intake runner slightly. Raising the injector kept the tip cleaner and the ball provided multiple seats to close off fuel flow. Because gasoline has such low viscosity, even minuscule pintle or ball movement is enough to release the amount of fuel the engine needs.

The Engine Control Module (ECM) or Powertrain Control Module (PCM) operates the fuel injectors, varying their delivery volume by the time it actuates their coils, the on-time or pulsewidth is measured in milliseconds. The computer calculates this time based on information from its sensors. These include the throttle position sensor, the engine coolant temperature sensor, the intake manifold pressure sensor, the mass airflow sensor, the crankshaft position sensor on 1996 Corvettes, and various other inputs depending on the year of your car.

Most fuel injection systems determine fuel pressure at the injectors by a combination of the fuel pump and the fuel pressure regulator. A fuel pressure regulator is used to release fuel back to the tank. The regulator’s return flow corresponds inversely to pressure in the intake manifold. As manifold pressure increases (increased load or low vacuum), the regulator returns less fuel back to the tank. As manifold pressure decreases (reduced load or high vacuum), the regulator returns more. The engine rarely uses all the fuel pumped.

At low coolant temperature, wide-open throttle, high load and high rpm, the engine burns almost all the gasoline the pump delivers. At high coolant temperature, idle and no load, the fuel pressure regulator returns most of the fuel back to the tank. This way, the difference between the pressure of the fuel in the rail and the pressure of the air in the intake manifold remains constant. With a constant pressure difference, the only variable determining the quantity of fuel injected is pulsewidth. This is the time the computer turns the injector on, allowing fuel to be injected.

As fuel re-enters the tank, it produces substantial vapour. With tighter emissions standards, 1999 and later Corvette fuel injection systems have no external pressure regulator or return line and run at a constant fuel pressure. It turned out to be easier to control fuel mixture at a constant fuel pressure (regardless of manifold vacuum/pressure) rather than to expand and complicate the charcoal canister vapour purge system. Fuel injectors on these ‘returnless’ fuel injection systems work the same as on the previous systems, but with shorter pulsewidths at low manifold pressure. When there is a greater difference between the fuel and the intake air pressure—at idle and deceleration—injector pulsewidth is extremely brief, or even non-existent.

Injector problems fall into two groups: mechanical and electrical. Bad fuel and water in the fuel have damaged many injector nozzles and/or pintle tips. You can identify mechanical problems by a visual inspection of the fuel spray pattern. Listening for an injector’s click (or its absence) can point to the first injector to observe. If grit or contaminated fuel gets past the main filter, they’ll quickly plug the small mesh filter in the top of the injector. Deposits formed from fuel droplets that evaporate after the engine shuts off can form gums and tars that clog an injector or skew its spray pattern, preventing the fuel from vaporising completely. Sometimes such deposits prevent the pintle from seating completely, so the injector dribbles fuel. While fuel cushions the injector pintles from closing against the seat, it’s still a mechanical part and will eventually show wear and begin to leak. Even the slowest unmetered fuel leak can often transmit more fuel than necessary at unloaded warm idle.

Rust and sediment in the fuel tank of 1982-1996 Corvettes damage many fuel injectors. The typical complaint would be difficult hot restarts. If the 1985-1996 Corvette fuel filler boot drain is plugged, water will accumulate and slowly be drawn into the tank. The 1982-1996 fuel tank has a plastic bladder, but the steel sending unit is prone to corrosion. This corrosion falls into the fuel tank, then the minute particles are forced through the fuel system to the fuel injector. The fuel filter will not stop these minute particles or water.

Most failed electrical circuits first become a short circuit and then quickly burn open, but with fuel injectors, you often notice drivability problems before the injector shorts completely. An injector that loses electrical resistance can have an interesting and puzzling effect. The usual way a coil changes resistance is by melting the thin insulation between adjacent windings of the wire. The failure does not occur all of a sudden. If the coil has 100 loops of wire, a short across the insulation between two loops can reduce the coil’s resistance by no more than one per cent, even if all the current went through the partial short circuit. Such a short may not noticeably affect the injector. It could be very hard to detect with even the best ohmmeter since new injector’s resistance varies more than that and temperature changes account for even more. As the resistance goes down, the current goes up, and as current goes up, so does the heat. The heat increase will melt the next most vulnerable insulation barrier until it also forms a short.

Before long, that partially shorted injector pulls noticeably more current than the others. It is rare for an injector to burn all the way shorted or open. The ECM or PCM will shut the injector off to protect the driver transistors when the current exceeds or falls below a certain threshold. Fuel injectors on 1985-1993 cars are grouped in two banks. The injector with lower resistance draws more current because electricity always follows the path of least resistance. Increased current to the partially shorted injector may ‘starve’ the paired injectors of current so it can’t lift its pintle and its cylinder gets little or no fuel. We then have the odd circumstance that the good injector does not spray long enough for combustion but the defective one keeps working—not for long, but long enough to leave

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