cat con guts burned out???

94 GMC AWD Safari Vortec W engine 4.3 I took it for a drive last week I couldnt make it there and back about 300 kms on one tank ouch. I was towing about 2000 lbs the check engine light was comming on and
off.....it seemed to run fine.....two years ago I replaced the o2 sensor because it was plugged up with carbon. I thought maybe the Cat converter was plugged so I got it cut out. It was wide open completely burned out same as a straight pipe. This van gets pretty close to spec milage except when I am towing. The mileage is brutal when towing is this normal? What is the most likely cause for the Cat con failer? What are the other two sensors called near the intake? Witch one is more likely to be bad? I might as well guess because the local guy here wants a arm and a leg to read for codes. ... and beside reading for a code will only tell me what I allready know It burns rich to much fuel gone forever.
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There is no shortcut here, get the codes.

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Like I said the local shop here wants more than one of the sensors alone. I have replaced the CPI and the o2 sensor allready. The CPI was leaking. What exactly does reading the codes tell ya? This would be a stored code because the light only comes on when it is towing. What is the cheapest way to read the codes on a 94 GMC?
Shep wrote:

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Isn't that vehicle OBD1? Short a couple of terminals in the connector block and count the flashes of the SES light? My 93 was like that.

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If it only fails towing a measly 2k pound trailer you better check the axle on the trailer as it is probably bound up. Guessing and throwing parts at it will cost you a lot more in the end. Have it diagnosed correctly. Any code that sets the Check light will leave a stored code.

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