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91 with no O2 sensor?

Discussion in 'The Garage' started by MR4WD, Jun 22, 2003.

  1. MR4WD

    MR4WD 1/2 ton status

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    A recent thread inspired this. I've got a 91 blazer, 350 with no accesories. The accessory belt only powers the water pump, power steering and alternator. There's no A.I.R. pump, or A/C. Should there be an A.I.R. pump? Furthermore, just before I bought the truck it had the exhaust replaced and the new exhaust came without an o2 sensor. Is there supposed to be one? Where in the harness does the o2 wiring feed back to if there is one?

    That would explain the poor fuel economy and rough idling issues I've been having, but I'm stumped as to why there isn't any check engine light glowing?

    Thanks for your help, Chad.
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I'm not sure what the reasons were but some earlier TBI trucks got the AIR and some didn't. My 88 1/2 ton with 350 and 5 speed did, but I have seen quite a few that didn't get any AIR pumps at all.

    It should have an O2 sensor though...

    Rene
     
  3. Chris Demartini

    Chris Demartini 1/2 ton status

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    <font color="blue">I dont have the ECM pinouts on hand right now, but the 02 is a single purple wire.
     
  4. captain chaos

    captain chaos 1/2 ton status

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    does the check engine light come on when you turn key on??

    reason i ask prevouse owner may have unhooked it.

    dave
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    I'd suspect the SES bulb has been removed or is dead.
     
  6. blasterD

    blasterD 1/2 ton status

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    I think A.I.R. pumps were only on California models. I'm not sure about Canadian models.
     
  7. rick88blaze

    rick88blaze 1/2 ton status

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    only trucks that came with california emissions will have the A.I.R. pump. mine came from missouri, and it had spent it's whole life there from brand new until i got it in 2000 and then i got transferred to las vegas 2 months after i bought it. and it's got that damn A.I.R. pump on it. as for the O2 sensor, i believe they should all have one.
     
  8. Thunder

    Thunder 3/4 ton status

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    You must have a 02 sensor for the fuel injection to operate properly. The ECM needs the feed back from the 02 so it can regulate the air to fuel mixture. Without the 02 the ECM goes into bypass mode, ignores most of the sensor input and runs on a pre programed set of operating values. This usually results in the problems you are having.
    You dont need the AIR system. But you do need to have all the sensors hooked up and operating for a FI system to work right.
    The 02 is usually located on the drivers side just below the exhaust manifold. Look around that area there should be a single wire connector hanging out.(unless someone clipped it off)
    As for the CE light if it does not come on when the key is turned on. The bulb is bad or has been removed.
     
  9. MR4WD

    MR4WD 1/2 ton status

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    The check engine light comes on until I start the vehicle. The light is fully operational. It does not function while the engine is running however. Thanks for the input, I find it novel that there is no o2 sensor and the truck still runs, albeit rough. I know vehicles pretty good, but I haven't torn into this blazer much. I rebuilt the winch, replaced the thermostat, knock sensor and coolant sensor. The last two were in hopes of fixing the erratic idle, and constant advance. It runs quite rich as well. I'll look around for purple wires that have been clipped and also look into welding in a bung for an o2 sensor.

    Again, thanks. I'll let you know how I make out.
     
  10. MR4WD

    MR4WD 1/2 ton status

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    Furthermore, I've also done the "put the paper clip in the diagnostic port and count the flashes trick", but that comes up with nothing. Just the self diagnostic code 42 or whatever the heck it was.
     

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