A8 Engine Performance / L1 Advanced Level ASE Test Preparation

 

Composite Vehicle
is equipped with either a MAP sensor or a MAF sensor.

RPM: is a magnetic pickup but the scan tool just shows the RPM

LOAD: the MAP sensor puts out an analog voltage. Idle at 18"Hg will give us 1.0 v, and wide open throttle with 0"Hg will put out 4.5 v. The MAF sensor option is also an analog voltage. Idle will be about 0.5 v and wide open throttle will be about 4.5 v

TPS: is an analog potentiometer that gives us a variable voltage, with 1.0 v at closed throttle idle, and 4.5 v at wide open throttle.

ECT: Engine coolant temperature sensor that is a negative coefficient thermister which gives 3.5 v at 32 degrees F and 0.5 v at 195 degrees F.

O2: Normal zirconium oxygen sensor where values below 0.45 v are leaner than 14.7:1 and values higher than 0.45 v are air-fuel ratios richer than 14.7:1.

LFTRIM: Given in %, where +% is adding time to the injector pulse width to richen the mixture, and -% is subtracting time from the injector pulse width. Normal values can be between + 10% and - 10%.  Maximum range is -25% to +25%.

 


Red Kap Automotive Mechanics Clothing

Scan Tool Diagnosis #1

The questions below have be reprinted with permission from Professor Steve McAfee, www.Smogsite.com

Composite Vehicle Specifications
are located on left side, under menu

 

1. Use the following scan tool data for this question. The engine is idling in the shop. It has a regular engine miss and has failed a smog inspection at idle with high CO. What is the likely problem with this engine?

Frame

-8

-7

-6

-5

-4

-3

-2

-1

0

TPS: (v)

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

MAP: (v)

1.3

1.3

1.3

1.3

1.3

1.3

1.3

1.3

1.3

ECT: (v)

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

O2: (v)

0.3

0.0

0.2

0.1

0.0

0.0

0.1

0.3

0.0

RPM:

800

800

810

800

810

800

810

800

800

INJ: (ms)

2.9

2.9

2.9

2.9

3.0

3.0

3.0

3.1

3.1

LFTRIM: (%)

+15

+15

+15

+15

+16

+16

+16

+17

+17

MAP sensor vacuum line fell off.
Fuel pressure too high.
ECT voltage too high.
Fouled #2 spark plug.

 

2. The engine runs very rich and gets very poor fuel economy. Using the scan tool information below, what is the likely problem?

Frame

-8

-7

-6

-5

-4

-3

-2

-1

0

TPS: (v)

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

MAP: (v)

1.1

1.1

1.1

1.1

1.1

1.1

1.1

1.1

1.1

ECT: (v)

4.7

4.6

4.7

4.7

4.8

4.7

4.7

4.7

4.8

O2: (v)

0.9

0.9

0.9

1.0

1.0

0.9

0.9

0.9

0.9

RPM:

800

800

810

800

810

800

810

800

800

INJ: (ms)

2.9

2.8

2.9

2.9

3.0

2.9

3.0

2.9

2.9

LFTRIM: (%)

-4

-4

-4

-4

-4

-4

-4

-4

-4

Poor electrical connection at ECT sensor.
Bad thermostat.
Low battery voltage.
Plugged catalytic converter.

 

3. A technician is driving a car with the scan tool connected and he records a glitch when the engine hesitated as he was cruising. What is the cause of the intermittent problem?

Frame

-8

-7

-6

-5

-4

-3

-2

-1

0

TPS: (v)

2.2

2.2

2.2

0.3

2.2

2.2

2.2

2.2

2.2

MAP: (v)

1.9

1.9

1.9

2.1

1.9

1.9

1.9

1.9

1.9

ECT: (v)

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

O2: (v)

0.7

0.3

0.8

0.0

0.0

0.7

0.8

0.2

0.4

RPM:

2600

2600

2600

2450

2550

2600

2600

2600

2600

INJ: (ms)

4.8

4.8

4.8

1.2

4.8

4.8

4.8

4.8

4.8

LFTRIM: (%)

+3

+2

+3

+0

+3

+3

+3

+3

+3

Intermittent O2 sensor connection.
MAP sensor intermittent.
TPS sensor intermittent.
Plugged catalytic converter intermittently.

 

4. A car owner complains of a lack of power when cruising. The emissions at idle look clean. During a road test with the scan tool our technician recorded the following data. Please look at it before answering the question: What's wrong?

Frame

-8

-7

-6

-5

-4

-3

-2

-1

0

TPS: (v)

3.1

3.1

3.1

3.1

3.1

3.1

3.1

3.1

3.1

MAP: (v)

3.4

3.4

3.4

3.4

3.5

3.5

3.5

3.5

3.5

ECT: (v)

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

O2: (v)

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

RPM:

1900

1900

1900

1900

1900

1900

1900

1900

1900

INJ: (ms)

6.4

6.4

6.4

6.4

6.5

6.5

6.5

6.5

6.5

LFTRIM: (%)

+20

+20

+20

+20

+20

+20

+20

+20

+20

Bad O2 sensor.
Plugged fuel filter.
Plugged air filter.
Bad MAP sensor.

 

 

5. A car has just failed a smog inspection and the customer also mentioned that the fuel economy had been really bad lately. Our technician recorded this scan tool data at idle while he noticed lots of black smoke coming out the tailpipe. What do you think is wrong?

Frame

-8

-7

-6

-5

-4

-3

-2

-1

0

TPS: (v)

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

MAP: (v)

1.1

1.1

1.1

1.1

1.1

1.1

1.1

1.1

1.1

ECT: (v)

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

O2: (v)

0.9

0.9

0.9

1.0

1.0

0.9

0.9

0.9

0.9

RPM:

800

800

810

800

810

800

810

800

800

INJ: (ms)

1.9

1.9

1.9

1.9

1.9

1.9

1.9

1.9

1.9

LFTRIM: (%)

-18

-18

-18

-18

-18

-18

-18

-18

-18

Fuel pressure regulator stuck closed.
Bad spark plug wire.
Engine coolant temperature sensor out of range.
Intake manifold vacuum leak.

 

6. The engine stalls intermittently. After several days, the technician captured a recording on the scan tool that showed scan tool data when the engine started to stall, but then caught itself and kept running. Here is what he found. What do you think is wrong?

Frame

-8

-7

-6

-5

-4

-3

-2

-1

0

TPS: (v)

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

MAP: (v)

1.1

1.1

1.1

1.5

1.1

1.1

1.1

1.1

1.1

ECT: (v)

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

O2: (v)

0.8

0.3

0.7

0.0

0.0

0.4

0.9

0.1

0.7

RPM:

800

800

810

0

610

800

810

800

800

INJ: (ms)

2.3

2.3

2.3

0

3.0

2.3

2.3

2.3

2.3

LFTRIM: (%)

+2

+1

+1

0

+2

+2

+2

+2

+2

Engine fuel injection stopped momentarily.
MAP sensor bad intermittently.
RPM magnetic pickup sensor bad intermittently.
TPS momentary glitch.

 

7. An engine appears to have several problems. When cruising, it wants to buck and jerk, has lots of hesitation when accelerating, and has a very uneven idle speed. It also surges at idle. But the engine doesn't miss regularly. The following data recording was taken at idle in the shop. Another clue: the exhaust emissions at idle have lots of HC and O2, even though this car doesn't have any air injection. What's wrong?

Frame

-8

-7

-6

-5

-4

-3

-2

-1

0

TPS: (v)

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

MAP: (v)

0.4

0.3

0.3

0.4

0.4

0.4

0.2

0.4

0.3

ECT: (v)

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

O2: (v)

0.1

0.1

0.0

0.0

0.0

0.2

0.1

0.1

0.0

RPM:

820

800

810

800

790

810

800

800

820

INJ: (ms)

1.8

1.7

1.7

1.8

1.8

1.8

1.6

1.7

1.8

LFTRIM: (%)

+5

+5

+5

+5

+5

+6

+6

+6

+6

Spark plug wire #3 has an open circuit.
EGR valve stuck partly open.
O2 sensor doesn't work.
MAP sensor out of range.

 

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