System Too Rich (Low Air/Fuel Ratio)

1987 Chevrolet Suburban R20, 7.4 N, 400/M40SECTION System Too Rich (Low Air/Fuel Ratio)

Idle speed too low. "SCAN" counts usually above 80. System obviously rich, and may exhibit Black smoke exhaust.

"SCAN" and/or voltmeter will read an oxygen sensor signal fixed above .80 volt (800 millivolts). Check for high fuel pressure, and/or leaking or sticking injector.

RENDER: 1.0x

NO RELATED

Recommended Tools & Savings

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Affiliate disclosure: We may earn a commission at no extra cost to you.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.