Katerina Swanson
If you're experiencing issues with your 1985 Corvette, it may be time to test the fuel injectors. A faulty fuel injector can cause a range of problems, from difficulty starting the car to poor performance and increased fuel consumption. To test the fuel injectors, you'll need to check the fuel pressure, inspect for any leaks or clogs, and verify the electrical connections. This may involve using tools such as a fuel pressure gauge, a mechanic's stethoscope, and a voltage meter. Additionally, you should pay attention to any unusual sounds or smells coming from the engine, as these could indicate a problem with the fuel injectors. By systematically checking these components and following the troubleshooting steps outlined in online forums and repair guides, you can identify and address any issues with your 1985 Corvette's fuel injectors.
| Characteristics | Values |
|---|---|
| Fuel pressure | 32-38 PSI with the vacuum hose connected, 42-48 PSI with the vacuum hose disconnected |
| Fuel injector type | Bosch 24 LB |
| Fuel pump | Should run for a few seconds when the ignition key is turned, bringing the fuel rail to ~40-43 Lb before cranking |
| Cold start injector | Should be tested for resistance (~12-14 Ohms) and a firing voltage at the harness |
| Throttle positioning sensor signal wire | Should be around .50 v at closed throttle |
| Injector testing | Can be done with a noid lamp or an ohm meter |
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What You'll Learn
Check the Throttle Positioning Sensor signal wire
To check the throttle positioning sensor signal wire, you will need to locate the wire first. For a 1985 Corvette, the throttle positioning sensor signal wire is blue. Once you have located the blue wire, you will need to test the voltage. A voltage of around 0.50 volts at a closed throttle is ideal. If the voltage is above 4.5 volts, the computer may interpret it as wide-open throttle (WOT) and shut off the injectors. However, it should not shut off the fuel pump.
To test the voltage, you can use a voltmeter. Connect the voltmeter to the blue wire and turn on the ignition. With the throttle closed, the voltmeter should read between 0.50 and 4.5 volts. If the voltage is within this range, the throttle positioning sensor signal wire is functioning correctly. If the voltage is above or below this range, there may be an issue with the wire or the throttle position sensor itself.
It is important to note that the throttle positioning sensor is just one of many components that affect fuel injection and engine performance. Other sensors, such as the mass airflow sensor, engine coolant temperature sensor, and manifold absolute pressure (MAP) sensor, also play a crucial role in calculating fuel injection. Therefore, if you are experiencing issues with your fuel injectors, it is recommended to check all relevant sensors and components, as well as fuel pressure and injector pulse.
Additionally, it is always a good idea to refer to a reliable repair manual or seek assistance from a qualified mechanic who can help diagnose and resolve any issues with your Corvette's fuel injection system. They will have the knowledge and tools to properly test and repair any issues with the throttle positioning sensor signal wire and other components.
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Test the cold start injector for resistance
The cold start injector is necessary to provide the extra fuel needed for a cold start. If the cold start injector isn't supplying the extra fuel, you may get intermittent firing, but the engine won't run. To test the cold start injector for resistance, you can follow these steps:
- Check the resistance - The resistance of the cold start injector can be tested using an ohm meter or a multimeter. The expected resistance value for a typical cold start injector is around 12-14 Ohms. If the measured resistance falls outside this range, the injector may be faulty and require replacement.
- Inspect for leaks - A leaky or sticking cold start injector can cause performance issues. Visually inspect the injector for any signs of leaks or blockages. If leaks are present, the injector may need to be repaired or replaced.
- Listen for the ticking sound - When the ignition key is turned to the "run" position, the cold start injector should fire. Use a mechanic's stethoscope to listen for a faint ticking sound coming from the injector. If no ticking sound is heard, it may indicate a problem with the injector or the fuel supply.
- Check the firing voltage - Ensure that the cold start injector is receiving the correct firing voltage at the harness. Refer to the vehicle's service manual or consult a professional mechanic to determine the specified voltage for your specific injector.
- Test the fuel supply - If the injector is firing but no fuel is being sprayed, there may be an issue with the fuel supply. Check the fuel lines for any obstructions or leaks. Ensure that the fuel pump is functioning properly and providing adequate fuel pressure.
- Consider the engine temperature - The cold start injector is designed to operate when the engine is cold. If the engine has been running for a while, the injector may not activate. Allow the engine to cool down and then retest the injector.
It is important to consult a qualified mechanic or refer to a vehicle-specific repair manual for detailed instructions on testing the cold start injector for resistance in your 1985 Corvette.
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Check for a firing voltage at the harness
To check for a firing voltage at the harness of a 1985 Corvette, you will need to test the injectors. Before you begin, ensure that you are wearing the correct safety gear and that you have the correct tools. This procedure should be performed with the engine off to avoid injury.
Firstly, turn the car on and turn the key to the second (ON) position. You want battery power flowing, but don't want the engine running. Set up a DVOM (Digital Volt Ohm Meter) to measure DC voltage. Use the lowest range possible if the meter doesn't auto-range.
Next, touch the negative lead of the DVOM to a ground source. The car's frame is connected to the ground, so look for an unpainted piece of the frame under the hood. Some DVOMs have alligator clips, which free up your hands to focus on getting the positive lead in the correct spot.
Now, place the positive lead on the wiring harness terminal. The wiring harness will have two terminals that the prongs on the injector insert into. One will be connected to the ground and will read 0 volts.
Repeat this process with all injector wiring harnesses. They should all be around 12 volts. A lower reading means there is excess resistance in the wire somewhere.
If you are having trouble with testing your injectors, it is recommended that you seek assistance from a certified technician.
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Check for correct flow at a lab
To check for correct flow at a lab, you can send your injectors to a fuel injector testing service. They will perform a series of tests to ensure your fuel injectors are operating correctly.
Firstly, ensure your injectors are externally clean and dry. A little brake cleaner can help with this. You will also need to fill out a service form and include it with your injectors.
The testing service will then perform a leak inspection, meticulously checking for leaks on the injector body and output nozzle. They will also perform ohm testing to verify the condition of the injector coil and test the resistance across the terminals of the injector connector.
Further tests include checking for inductance, shorts, and current draw. The spray pattern and injector flow rate will also be tested and recorded.
After testing, the injectors are lubricated and sealed in poly bags. A comprehensive test report is then prepared and returned with the injectors.
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Check for power at the spark plugs
To check for power at the spark plugs of your 1985 Corvette, you will need to inspect the spark plugs and their wires for any damage or abnormal readings.
Firstly, remove the distributor cap and turn over the engine. If the rod moves, the gear is not the issue. If there is no spark at the plugs, the coil may be faulty, or the wires may not be clean or connected properly. Ensure the coil wire is tight on the cap. There may even be a broken wire between the coil and distributor.
The spark plugs themselves may be worn out, as they naturally degrade over time. They can also be fouled by rich fuel mixtures or fuel additives, or contaminated by oil. Check the spark plugs for any signs of damage or heavy carbon build-up. If the spark plugs are in poor condition, they should be replaced.
If the spark plugs are functioning, but the engine is still not starting, you may need to test the ICM. If the ICM is faulty, the engine will not start, and you will need to replace it.
You can also try using a timing light to check for flashes. If you see flashes, the pickup coil and ICM are functioning correctly. If there are no flashes, you should measure the pickup coil resistance. If the resistance is abnormal, the ICM may be failing, especially when it gets hot.
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Frequently asked questions
If your 1985 Corvette only starts when you pour fuel down the throttle body, it may have a faulty cold start injector or the fuel rail isn't being pressurised during the start-up procedure.
You can test the cold start injector for resistance (~12-14 Ohms) as well as check for a firing voltage at the harness. If the injector is firing, you can hear a faint ticking sound using a mechanic's stethoscope. You can also check your injectors with a noid lamp, hooking it up one injector at a time to detect pulses.
If your Corvette is hard to start, it could be due to a leaking fuel injector, coolant temp. sensor, oxygen sensor, or fuel pressure regulator. You should also check the throttle positioning sensor signal wire (the blue wire) and ensure it is around .50 v at closed throttle.
The fuel pressure for the 1985 Corvette should be 32-38 PSI with the vacuum hose connected, and 42-48 PSI with the vacuum hose disconnected.
