Checking for a bad catalytic converter

Tiny
RAPS56
  • MEMBER
  • 2002 SATURN SL2
  • 1.9L
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 95,000 MILES
Using a thermometer gun do I put the red dot on the pipe going in and out or on the catalytic converter itself near the in and out?
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Friday, March 24th, 2017 AT 3:12 PM

7 Replies

Tiny
CARADIODOC
  • EXPERT
What are you trying to test? '96 and newer models have a second oxygen sensor after the catalytic converter so the Engine Computer can monitor the converter's efficiency. If the efficiency goes down too far, a diagnostic fault code will be set related to "Catalytic converter efficiency", and since it pertains to something that could adversely affect emissions, the Check Engine light will be turned on.
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Friday, March 24th, 2017 AT 3:29 PM
Tiny
RAPS56
  • MEMBER
50 MPH mid throttle it starts bucking and check engine flashes looses power let off the throttle and it is OK or full throttle is OK someone said maybe clogged catalytic converter. Not sure.
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Friday, March 24th, 2017 AT 4:20 PM
Tiny
JOHNNY G.JR
  • MEMBER
Scan for codes
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Friday, March 24th, 2017 AT 4:52 PM
Tiny
RAPS56
  • MEMBER
No codes
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Friday, March 24th, 2017 AT 5:08 PM
Tiny
CARADIODOC
  • EXPERT
If the converter was plugged, you wouldd have almost no power at full-throttle. The major clue that you should have included right up front is the flashing Check Engine light. That indicates the most serious of defects has been detected. You are supposed to stop the engine right away and let the exhaust system cool down. Too much un-burned fuel is going into the exhaust system where it will burn in the catalytic converter, and that can melt the catalyst into a glob that restricts flow.

Most commonly that un-burned fuel in the exhaust is the result of a spark-related misfire, and that is most commonly due to worn spark plugs and wires. For engines that use the "coil-on-plug" design, a failing ignition coil can do this too.

Two additional symptoms of a plugged converter are the engine will run unusually smoothly, and you will hear a steady hiss from the tail pipe instead of the normal "putt putt" sound.

Regardless of the combination of symptoms, when there are no diagnostic fault codes to indicate the circuit or system that needs further diagnosis, you can use a scanner with "record" capabilities to take a snapshot of the sensor readings. During a test-drive, the "record" button is pressed when the problem occurs. Because the data passes through the scanner's memory, the recording actually begins a couple of seconds before the button was pressed. Later, that recording can be replayed slowly to see what changed. You may see a momentary glitch or dropout from an "input" sensor, or you may see something unusual from an "output" sensor, in this case, the oxygen sensors. The Engine Computer calculates fuel volume, injector timing, and spark timing based on the input sensor readings. Output sensor readings tell the computer what the results were of those calculations.
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Friday, March 24th, 2017 AT 6:06 PM
Tiny
RAPS56
  • MEMBER
When the light is flashing the car surges and loses power from 60 mph to35 mph if I let off the throttle then go almost full throttle it will go back to full power and if I pump the throttle it will get by it
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Friday, March 24th, 2017 AT 7:05 PM
Tiny
CARADIODOC
  • EXPERT
The simple observation it is able to go back to full power eliminates the catalytic converter as a suspect.
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Friday, March 24th, 2017 AT 7:10 PM

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