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Thread: 94 Bonneville SLE Sudden Severe Power Loss

  1. #1
    Carb and Points!
    Join Date
    May 2015
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    94 Bonneville SLE Sudden Severe Power Loss

    Recently, from a steady 35 mph my '94 SLE suddenly lost severe power and I could hear loud exhaust-type sounding noise from the front half of the vehicle. We "crawled" home at a few mph for about a mile.

    During inspection of the underside of the vehicle I noticed that the outlet pipe of the catalytic converter had fractured (a full 360 degrees) about an inch from the converter due to corrosion and stress. Also, by looking into the outlet end of the catalytic converter I noticed the honeycombs at that end are not plugged and appeared quite clean.

    Background information: About two weeks prior to this incident, a technician read a P1406 history code (Exhaust Gas Recirculation Pintle Position Sensor Circuit) off of the vehicle. In addition, tonight I recorded data from the ECM using an OBD Diagnostics cable and TunerPro software on my laptop when test driving up our driveway from idle. The EGR Pos increased from 1.6% to a sporadic behavior peaking as high as 50%, the CCP Cycle increased from 13% to 34%, and the spark advance changed from 29 degrees to 26.5 degrees. Also, the airflow increased from 5 grams/sec to 11g/sec, the RPM increased from 730 rpm to 1050 rpm, the fuel base pulse increased from 4.25 ms to 6.75 ms, and the coolant temp was 180 F.

    Please provide your thoughts on what may be causing the severe power loss. Also, if I must, is it OK to drive it to a shop? Thanks, in advance.

  2. #2
    Fuel Injected!
    Join Date
    Oct 2014
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    40
    Quote Originally Posted by Karms20 View Post
    Recently, from a steady 35 mph my '94 SLE suddenly lost severe power and I could hear loud exhaust-type sounding noise from the front half of the vehicle. We "crawled" home at a few mph for about a mile.

    During inspection of the underside of the vehicle I noticed that the outlet pipe of the catalytic converter had fractured (a full 360 degrees) about an inch from the converter due to corrosion and stress. Also, by looking into the outlet end of the catalytic converter I noticed the honeycombs at that end are not plugged and appeared quite clean.

    Background information: About two weeks prior to this incident, a technician read a P1406 history code (Exhaust Gas Recirculation Pintle Position Sensor Circuit) off of the vehicle. In addition, tonight I recorded data from the ECM using an OBD Diagnostics cable and TunerPro software on my laptop when test driving up our driveway from idle. The EGR Pos increased from 1.6% to a sporadic behavior peaking as high as 50%, the CCP Cycle increased from 13% to 34%, and the spark advance changed from 29 degrees to 26.5 degrees. Also, the airflow increased from 5 grams/sec to 11g/sec, the RPM increased from 730 rpm to 1050 rpm, the fuel base pulse increased from 4.25 ms to 6.75 ms, and the coolant temp was 180 F.

    Please provide your thoughts on what may be causing the severe power loss. Also, if I must, is it OK to drive it to a shop? Thanks, in advance.
    All the values you scanned WILL change while driving, so saying the value changed from x to y while driving in your driveway isn't that helpful, as a change would be expected.
    As long as you aren't seeing Severe Misfire, its probably OK to drive to the shop, as long as the exhaust leak at your Cat isn't near anything flammable.

  3. #3
    Carb and Points!
    Join Date
    May 2015
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    Edfiero1, thanks for the quick reply. My catalytic converter was almost completely plugged; I could barely see light looking through either the converter inlet end or outlet. Interestingly, the inlet and outlet honeycomb areas showed no signs of being plugged. Is it normal for the honeycombs to plug-up on the inside? Could that be a clue as to the cause? The installed Magnaflow Universal Converter (#94016) has eliminated the power loss.

    Looking forward, my research found that "replacing a bad converter will only temporarily restore things to normal because unless the underlying problem that caused the original converter to fail is identified and fixed, the replacement converter will likely suffer the same fate."

    With that in mind, have you, or anyone else, found the cause of a converter plugging-up? What are some areas to consider (e.g.,unburned fuel, burning oil, burning coolant)? Thanks again.

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