94 Bonneville SLE Sudden Severe Power Loss

['TilWheelsFallOff]

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.

[96 SSEi]

Hi, I had the same power loss on my 96 ssei, turned out to be plugged cat, the front will plug first and work its way back to the cat rear. If you can, unbolt the cat studs allowing exhaust to escape and see if the power returns, you can drive to shop like this but car will be loud. I d rove about 30 KLM to get new cat
Happy trails.....

['TilWheelsFallOff]

96 SSEi, thanks for the quick reply. You were correct, 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? 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, did you, or anyone else, find the cause of your converter plugging-up? What are some areas to consider (e.g.,unburned fuel, burning oil, burning coolant)? Thanks again.

[RJolly87]

How many miles on this car?

20 years is a pretty good run for a catalytic converter...

Just make sure that the engine is in good tune (plugs, wires, o2 sensor, etc) and isn't burning anything (oil, coolant, etc) and then don't worry about it.

[96 SSEi]

Hey wheels, glad I could be of some assistance -even a. Broken clock is correct twice a day... lol
I toasted my cat due to sheer stupidity-spraying carb cleaner in the throttle body and started the engine
I know better now, remove, then clean and replace

You throwing any codes, ses light on?


Glad to hear you're roaring again............. keep smiling man!!

['TilWheelsFallOff]

Jolly, the car only has 80,800 miles. A couple of months ago, I replaced the plugs & wires. I am slowly losing coolant; I can smell it in the engine compartment after vehicle use. However, the system held 15 psi with a pressure tester.

96 SSEi, I do have an intermittent SES light. The code is P1406 (EGR Pintle Position Sensor Circuit). The car idles fine, but sometimes hesitates when accelerating from a stop or from a low vehicle speed. Also, sometimes around a constant 30 mph the engine speed will fluctuate +/- 25 rpm or sometimes it feels like it's missing at constant vehicle speeds above that.

Thanks to both of you for your help & interest. I greatly appreciate it. (Should either of the above two paragraphs be a new topic? Sorry, I'm new at this.)

[RJolly87]

Slowly losing coolant is a point of concern, and something you will want to track down pretty quickly. You'll want to scrutinize the throttle body gasket (signs of coolant in the intake, past the throttle body) the area where the LIM meets the UIM, directly below the throttle body, as well as coolant bypass hose, fitting, heater hose outlet, etc.

Also make sure there is no coolant in the oil.

If the engine is ingesting coolant, that can account for the driveability issues, however those can very well be caused by a sticking EGR valve or other EGR issues.

You may need to clean the engine bay really well, add dye to the cooling system, and track it down with a UV light. Oil analysis will rule out any coolant going to the oil (or confirm it)