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Thread: Missing sensors

  1. #1
    Senior Member EXPERT BUILDER
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    Missing sensors

    I have a 2000 BBC 3500 4 dr.Chev.Truck thats missing the 2 sensors aft of the last muffler.I did take the VIN to chev & the drawing they provided me shows them to be there.Mine have plugs in them..I cant find any trace of a wiring harness--It gets 10 to 11 miles per gal at 55-with or without trailer??Thats what started me looking for the sensor problem..it gets the same milage with.without a trailer-Im to understand the front & rear sensors telle the computer wheather its rich or lean--Without them it retards the timing & increases the fuel?Any help provided will be greatly appreciated--

  2. #2
    Senior Member EXPERT BUILDER gearhead1011's Avatar
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    Re: Missing sensors

    Quote Originally Posted by wlpatterson
    I have a 2000 BBC 3500 4 dr.Chev.Truck thats missing the 2 sensors aft of the last muffler.I did take the VIN to chev & the drawing they provided me shows them to be there.Mine have plugs in them..I cant find any trace of a wiring harness--It gets 10 to 11 miles per gal at 55-with or without trailer??Thats what started me looking for the sensor problem..it gets the same milage with.without a trailer-Im to understand the front & rear sensors tell the computer wheather its rich or lean--Without them it retards the timing & increases the fuel?Any help provided will be greatly appreciated--
    The only sensors that are used in the exhaust are oxygen sensors. Anything behind the catalytic converters would be for monitoring converter performance, they will have no effect on performance or fuel mileage. The sensors used for fuel control are as close to the manifolds as possible and would have to be in front of the converters. I would think it should have them but if it's not turning on a check engine light then it's possible that those may not have been used on that truck from the factory. If they were missing there would have to be simulators installed or the program on the computer would have to be altered to keep the check engine light off. Those trucks with the bb in them get terrible mileage, that's probably all it will get.

  3. #3
    Senior Member RACING JUNKIE
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    I've got a similar problem with 1993, 3500 crewcab. it has a wire hanging down near the sensor, one sensor wire is plugged in, but there's no place to plug the other one in. It also gets 10 to 11 mpg but at 70 mph, gets about 7 with 28ft halmark loaded. If i pull my flat bed trailer with car on it the truck doesn't even know it's back there and get over 10mpg. BUTTT!! when the truck is first started the check engine light is off and it runs really good, but after a few miles driven the check engine light comes, and there is a noticeable difference in the performance on the bottom end, but no change in gas milage. No one around here has a plug in for the computer so i don't know what code it is.

    Zip.

  4. #4
    Senior Member RACING JUNKIE
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    I would think that anything w/a Cat. & ECU will have O2 sensor... many rigs have (2) O2 sensors.

    Zip: I am no expert on this subject, but your dillema sounds like a crank-shaft sensor. Had a problem like once myself...

    My Stock 4wd chevy truck (w/a manual trans) gets 10 miles to the gallon... consistenly. It has 33" tires/373 gears & a small lift... 97,000mi always 10 miles to the gallon.
    "I would walk through hell on Sunday before I fear the enemy"

  5. #5
    Senior Member EXPERT BUILDER gearhead1011's Avatar
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    Quote Originally Posted by zipper06
    I've got a similar problem with 1993, 3500 crewcab... .... No one around here has a plug in for the computer so i don't know what code it is.

    Zip.
    You can jumper 2 of the terminals in the diagnostic connector on that truck and count check engine light flashes for trouble codes. Let me know if you need details.

    Quote Originally Posted by Rigsby
    I would think that anything w/a Cat. & ECU will have O2 sensor... many rigs have (2) O2 sensors.
    Most vehicles with V6, 8 or 10 built after 95 (OBD II) have at least 3. There should 1 for each bank near the manifold and one behind each converter. Some have a convertor (or 2) for each bank and some route both banks through a single converter. There should be a sensor at the rear of each converter unless the converters are run in line then it will have a sensor behind one of the converters. I have never seen anything with more than 4 sensors. I have seen some exceptions but this the way most of the OBDII vehicles are set up.

    Reading over the 1st post in this thread I noticed you stated it's "missing the 2 sensors aft of the last muffler". Usually the rear sensors are in the pipe right behind the converter not the muffler. You should look to see if it has any sensors behind the converter(s). If it does then it shouldn't need anything behind the muffler.

  6. #6
    Senior Member EXPERT BUILDER
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    sensors

    Im sorry,I meant behind the converter

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