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10.
INSPECT CO/HC
(a)
Start the engine.
(b)
Race engine at 2,500 rpm for approx. 180 seconds.
(c)
Insert CO/HC meter testing probe at least 40 cm (1.3 ft) into tailpipe during idling.
(d)
Immediately check CO/HC concentration at idle and/or 2,500 rpm.
HINT:
Complete the measuring within 3 minutes.
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When doing the 2 mode (idle and 2,500 rpm) test, these measuring orders are prescribed by the appli-
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cable local regulations.
(e)
If the CO/HC concentration does not comply with regulations, troubleshoot in the order given below.
(1)
Check heated oxygen sensor operation. (See page 12–6)
(2)
See the table below for possible causes, and then inspect and correct the applicable causes if
necessary.
CO
HC
Normal
High
Low
High
High
High
2004 COROLLA (RM1037U)
ENGINE MECHANICAL
(4)
HINT:
If adding oil helps the compression, it is likely that the pis-
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ton rings and/or cylinder bore are worn or damaged.
If pressure stays low, a valve may be sticking or seating
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is improper, or there may be leakage past the gasket.
Problems
3. Faulty ignitions:
S Incorrect timing
S Fouled, shorted or improperly gapped plugs
Rough idle
4. Incorrect valve clearance
5. Leaky intake and exhaust valves
6. Leaky cylinders
1. Vacuum leaks:
S PCV hoses
S Intake manifold
Rough idle
S Throttle body
(Fluctuating HC reading)
S ISC valve
S Brake booster line
2. Lean mixture causing misfire
1. Restricted air filter
2. Plugged PCV valve
3. Faulty EFI systems:
S Faulty pressure regulator
Rough idle
S Defective water temperature sensor
(Black smoke form exhaust)
S DEFECTIVE Air–flow meter
S Faulty ECM
S Faulty injectors
S Faulty throttle position sensor
–
ENGINE ASSEMBLY
If the cylinder compression in one more cylinders is
low, pour a small amount of engine oil into the cylin-
der through the spark plug hole and repeat steps (1)
through (3) for cylinders with low compression.
Causes
14–3
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