Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Fuel Controls
The engine is equipped with a feedback carburetor. I-Mark models contain vacuum-operated fuel control actuators. ECM responding to inputs from the data sensors and constantly adjusts the air/fuel ratio to maintain engine performance.
The ECM sends electrical signals to a vacuum control valve or M/C. The vacuum control valve converts the ECM signals to vacuum signals to operate the actuators. The M/C solenoid adjusts the carburetor mixture directly.
The vacuum control valve consists of a vacuum regulator and a vacuum control solenoid. The regulator changes the inconsistent vacuum levels from the intake manifold into constant vacuum levels. The vacuum control solenoid, controlled by the ECM, uses the vacuum from the regulator to operate the fuel control actuators.
When the ECM responds to signals received from oxygen sensor, the system is in Closed Loop operation. Under certain operating conditions, the ECM may ignore inputs from various data sensors and use a pre-programmed calibration control to operate the engine under that particular condition.
During cold engine starts, the vacuum control or M/C solenoid is turned off by the ECM to provide a rich mixture. Operating conditions which cause the ECM to ignore oxygen sensor signals cause the system to operate in the open loop mode.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.