Question

all of the following conditions lead to a black colored exhaust except:

a. a leaking or sticking fuel injector.

b. a leaky vacuum diaphragm on the fuel pressure regulator.

c. an open coolant temperature sensor circuit.

d. a blown head gasket.

Explanation:

• A leaking or sticking fuel injector (a) causes an overly rich fuel mixture, leading to black exhaust.
• A leaky vacuum diaphragm on the fuel pressure regulator (b) can result in a rich fuel mixture (higher fuel pressure), causing black exhaust.
• An open coolant temperature sensor circuit (c) may cause the engine computer to think the engine is cold, enriching the fuel mixture and potentially leading to black exhaust.
• A blown head gasket (d) typically causes coolant to enter the combustion chamber (white - colored exhaust smoke if coolant is burned) or oil - related issues (blue smoke if oil is burned), not black exhaust from a rich fuel mixture.

Answer:

d. A blown head gasket.