How to Teach NoCode Diagnosis

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How to TeachNo-Code Diagnosis

• A Step by Step Guide to Success
• James D. Halderman

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What should a service technician do first?

• Verify the customer concern.
• Check for any DTCs.
• Perform a thorough visual inspection.
• Check for any TSBs.
• Look carefully at scan tool data (PID or
  Parameter Identification).

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What should a service technician do first?
(continued)

• Narrow the problem to a system or a cylinder.
• Repair the problem and determine the root cause.
• Verify the repair and clear any DTCs.

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P0304 Example
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Egr passage problem is shown.
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Remove upper plenum for EGR inspection.
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5 out of 6 are stopped up!
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Could this condition have been prevented?

• Maybe, if carbon cleaning had been done
  regularly.
• Maybe, if a dispersant such as Techron
  (polythermine) had been added to the fuel tank
  twice a year to keep carbon particles from
  combining.
• Maybe, if the vehicle had been driven less in the
  city and more on the highway.

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Linder Technical Services

• Offers reconditioned fuel injectors and
  technician training.
• www.lindertech.com

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Code Diagnosis Procedures

• Try to set the opposite code.
• If DTC is TP sensor low, try to set TP sensor
  high by using a jumper wire between the 5-volt
  reference (gray wire GM) and the signal wire(
  dark blue GM).

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Code Diagnosis Procedures (continued)

• If the opposite code does set, then the problem
  is the sensor itself.
• If the opposite code does NOT set, then the
  problem is due to a fault in the wiring or the
  computer.

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Hands-On Activities

• Set a code
• Retrieve a code
• Erase a code

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Brake Pedal Trick

• Depress the brake pedal after disconnecting the
  negative battery cable to clear all memory.
• Clears all memory without doing harm except for
  the loss of radio and other stored data.

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Black Pontiac Grand Prix Story (1997 3100 V-6)

• Missing at idle on cylinders one, three, and five
  only.
• When first started, I noticed slow, jerky
  cranking even with the ignition disconnected
  (this was not a customer concern).
• What would you do first?

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Visual inspection discovered a corroded cable.
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Injector inspection showed that the wiring for
the front and rear banks were switched.
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ATF was used through the intake to check to see
if the valves were sticking.
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The rear O2S was replaced because it failed the
KOEO test. (described later)
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Spark testers were installed to check the
ignition system for proper operation.
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Based on information from the archives of www.
iatn.net, the intake gasket area was checked for
possible leaks.
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Spraying around the injector O-rings caused a
misfire.
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Checking the misfire counters confirmed that we
had discovered the root cause.
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Final Result

• Replacing the injector O-rings solved the misfire
  on cylinders 1, 3, and 5.
• Switching the injector harness back to the
  correct bank of the injectors solved the slow,
  jerky cranking problem.

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What I Learned

• I learned to use the misfire counter whenever
  working on a possible engine miss.
• The misfire counters picked up misfires that
  could not be detected otherwise.

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Scan Tool Data Stream Sequence

• Key on, engine off check that ECT equals IAT.
• MAP should also equal BARO.
• Normal reading is between 4.6 volts and 4.8 volts
  depending on weather conditions and altitude.

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KOEO Oxygen Sensor Test

• Look at O2S sensor voltage when the engine is
  cold and the ignition is first turned on.
• The heaters will cause the O2S to become
  conductive and the bias voltage will be gradually
  lowered as the sensors heat.
• Look for a sensor that fails to achieve a voltage
  of less than 100 mV after three minutes.

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KOEO Oxygen Sensor Test (continued)

• A post-catalytic converter O2S will cause a
  driveability concern because the primary function
  of OBD II is to control exhaust emissions. If
  the rear O2S goes high, the PCM will try to make
  it go low by removing fuel, which can cause a
  driveability concern and no DTCs. (This
  information came from field engineers.)

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Hands-On Activities

• Key on engine off O2S test
• Key on engine off IAT and ECT test

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Fuel Pump Pressure Test

• All fuel pumps should produce a maximum pressure
  (deadhead pressure) about two times the operating
  pressure.
• Normal operating pressure is 35 psi to 45 psi.
• Maximum pump pressure should then be between 70
  psi and 90 psi.

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Checking Fuel Pressure

• Connect the gauge to the Schrader valve.
• Record the pressure with engine at idle speed.

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Checking Fuel Pressure (continued)

• Rapidly accelerate the engine and watch the
  pressure gauge.
• If the pressure drops more than 2 PSI, the fuel
  filter is partially clogged or the pump is weak.

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Current Ramping Fuel Pumps

• Requires a digital storage oscilloscope and a
  current clamp.
• Tie into the fuel pump relay or fuel pump fuse.

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Current Ramping Fuel Pumps (continued)

• Operate the fuel pump and determine time per
  revolution (8 segments in 6 ms).
• Divide time in milliseconds into 60,000 to
  calculate pump RPM (10,000 RPM).

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What is the purpose of the fuel module?
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Hands-On Activities

• Have students current ramp their fuel pumps.
• Check for speed (should be 3,000 RPM)
• Check for current draw TBI 3 to 5
  A Port 4 to 7 A GM Central Port 8 to
  12 A

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Stethoscope Testing
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Quick and Easy Test

• Remove fuel pump relay and install a fused jumper
  lead between terminals 30 and 87.
• Use a stethoscope and listen for fuel returning
  to the fuel tank.
• If fuel is not heard, then either the pump is
  weak or the regulator is defective.

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Hands-On Activities

• Have students listen to injectors using a
  stethoscope.
• Have students use a fused jumper test lead and
  operate the fuel pump without the engine running
  and then listen for fuel at the outlet of the
  fuel pressure regulator.

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Fuel Injector Voltage Waveform

• Inductive spike should exceed 30 volts.
• DC offset should be less than 200 mV.
• Injector pulse width should be 1.5 to 3.5 ms at
  idle or 2000 RPM in Park/Neutral.

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A Good Injector Voltage Waveform
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A Shorted Injector Waveform
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Hands-On Activities

• Have students use a scope to check the waveform
  of injectors on their vehicles.
• Take digital photos of scope display.
• Show entire class the results of the testing
  using a TV to show the digital photos.

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Fuel Injector Current Ramping

• The slope should be about 60 degrees.
• The pintle should open about two-thirds of the
  way up the slope.
• If the pintle opens later, it may be dirty.
• If the pintle opens too soon, the spring may be
  broken.

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Bug-Debug Hands-On Activities

• Do no harm.
• Must be verified using scan tool tool data.
• Write R.O. with the customer concern.
• Bug team must restore vehicle to proper
  operation.
• Hood will remain down so bug does not need to be
  hidden.

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Five Gas Exhaust Analysis

• HC-less than 30- 50 PPM
• CO less than 0.3 - 0.5
• CO2 should be 12 - 17
• O2 should be 0.0 - 2.0
• NOx should be less than 100 PPM at idle and less
  than 1,000 PPM at WOT

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If HC Only Is High

• Usually caused by spark stuff (plugs, wires,
  timing etc.).
• Can also be caused by a cool operating engine (
  thermostat).

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If CO Is High

• CO is the rich indicator.
• Could be clogged oxygen (dirty air filter,
  PCV).
• If rich enough, the HC will also increase.

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If O2 Is High

• O2 is the lean indicator.
• The higher the leaner.
• Look for a vacuum leak.
• If high at idle and OK at 2,000 RPM, look for a
  hole in the exhaust system.

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CO Should Equal O2

• If the air-fuel mixture is OK, then both CO and
  O2 should be low.
• If CO is higher than O2 , the mixture is rich.
• If O2 is higher than CO, the mixture is lean.

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CO2 Should Be High

• The higher the CO2, the more efficient.
• If the CO2 is low, the air-fuel mixture could be
  either rich or lean.
• Look at CO and O2 levels to determine if rich or
  lean.

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NOx

• NOx should be less than 100 PPM at idle.
• NOx should be less than 1,000 at WOT.
• If NOx is higher, the vehicle could fail an
  enhanced IM test.
• Excessive NOx is caused by the engine operating
  either too hot or too lean.

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Hands-On Activities

• Have students check the exhaust emissions on
  their own vehicle.
• Ask them if the CO is equal to the O2.
• If emissions are high, have them decarbonize and
  retest.

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Thanks

• For further information, consult these web sites
• www.autoclassroom.com
• www.lindertech.com
• www.asetestprep.com

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Questions?
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Jim Halderman jim_at_jameshalderman.com