The fuel injection in a 1988 Dodge W150 TBI system is a
pulsed spray (intermittent) system, not a steady spray.
The Powertrain Control Module (PCM or computer) sends a pulsing signal to the injector(s) to control the amount of fuel delivered. The duration of each pulse, known as "pulse width," is varied by the computer based on sensor inputs (like the O2 sensor and engine temperature) to achieve the correct air/fuel ratio for different operating conditions (e.g., idle vs. wide open throttle).
A steady spray typically indicates a fault in the system, such as a stuck injector or wiring issue. You should be able to use a 12-volt test light or an oscilloscope to observe the pulses when the engine is cranking or running
A 1988 Dodge W150 running rich with TBI is often caused by faulty sensors like the O2 sensor or coolant temperature sensor, a leaking fuel pressure regulator, or leaking injectors. Other causes can include vacuum/intake leaks, faulty grounds, or a failing Idle Air Control (IAC) valve. The air/fuel ratio on these vehicles is computer-controlled, so a rich condition points to a component sending incorrect data or a physical leak.
Common causes and their solutions
- Faulty sensors:
- O2 sensor: A bad O2 sensor can cause the computer to enrich the mixture.
- Coolant Temperature Sensor: A failing coolant sensor can make the computer think the engine is always cold, leading it to continuously enrich the mixture.
- Fuel delivery issues:
- Fuel Pressure Regulator: A faulty regulator can fail to control fuel pressure, flooding the engine with too much fuel.
- Leaking injectors: The O-rings on the TBI injectors are a common failure point and can leak fuel directly into the intake.
- Leaks:
- Vacuum leaks: A leak in the intake manifold or vacuum lines can cause the computer to try and compensate, leading to a rich condition.
- Electrical issues:
- Bad grounds: Poor grounds can cause the computer and sensors to malfunction, leading to incorrect readings and a rich mixture. It's crucial to check the main grounds on the engine block and firewall.
- Idle Air Control valve (IAC): A stuck IAC can cause an issue with idle control, which can affect the air/fuel mixture.
How to diagnose
- Check for codes: Use an OBD1 scanner to check for diagnostic trouble codes, which can point you directly to a faulty sensor.
- Inspect sensors: Test the O2 sensor and coolant temperature sensor to ensure they are providing accurate readings.
- Inspect for leaks: Check the fuel pressure regulator, injector O-rings, and vacuum lines for any leaks or damage.
- Inspect electrical connections: Thoroughly inspect all ground wires and sensor connectors for corrosion or damage
