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MAF and O2 on TBI issues

Discussion in 'The Garage' started by AudioMaster, Apr 7, 2005.

  1. AudioMaster

    AudioMaster Registered Member

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    I just got my hands on an '87 k5 Jimmy for an increadable deal. Part of the reason is it runs like crap. The previous owner had Doug Thorley headers and a dual exaughst put on a couple of months ago. When he got the truck back he realized that it wasn't running as well as it did before. He opened the hood and noticed a different air cleaner was on the truck and his factory cold air tube was gone.

    Further inspection showed that the headers not only didn't have the bung for the O2 sensor but there was no O2 Sensor just a cut wire. Same story on the MAF.

    The aircleaner was different and had no MAF (if that's even where it goes) just another cut wire.

    Now that's the history. My questions are this:
    Can I just get ahold of a bung, weld it to the header or should I put it down at the collector and install the 02 sensor?

    What are my options for a MAF? Where does it go? Should I go to a salvage yard and get a stock aircleaner pan?

    Thanks in advance, here are some engine bay pics:

    S3010111.JPG

    S3010112.JPG
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Actually you are looking for a MAP sensor. MAP can be mounted pretty much anywhere.

    That looks like a stock TBI aircleaner to me. Just flip the lid over if it will fit, and get the snorkel for it.

    O2 sensor you really want as close to the engine as possible, but you also want to see all 4 cylinders on that side, so with headers that may limit you somewhat. You can buy the O2 sensor bung many places, or if you want to save money but spend time, you can get the right metric nut and cut it down. You want the O2 sensor into the exhaust stream as much as possible the way I look at it.

    Once you get the O2 and the MAP back in place, hopefully you'll be good to go. Are you getting a check engine light, and is the ECM still in place behind the glovebox? If you aren't getting a check engine light (ever) then there is another issue, hopefully just the bulb removed.

    Edit: and they didn't hook the breather back up right either. (passenger side valve cover to the air cleaner)
     
    Last edited: Apr 7, 2005
  3. Jonny-K5

    Jonny-K5 1/2 ton status

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    thats the stock air cleaner, the lid is just flipped upside down. i dont know why they would take the liberty of doing this and tossing the air inlet tube. i've tried flipping the lid on my truck, you can hear the intake sucking air more, but doesnt really help in power. maybe they were thinking it needed more air since it was exhaling better with the headers? :dunno:

    i dont think these trucks have a MAF sensor, they use a MAP sensor. i think its in the throttle body. no sensor goes in the air cleaner. not sure what cut wire your seeing there. maybe take a pic of it

    you can weld in a bung for the o2, not sure where the most ideal place is, but collector would be good.

    once you put a o2 sensor back in it should run good.
     
  4. sled_dog

    sled_dog 1 ton status

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    the MAP sensor is located outside of the intake(and throttlebody). It is the black box thing on the passenger side of the intake manifold. It ports into either the intake or one of the throttle body ports to get its vaccum/pressure readings. I forget which one it goes to off the top of my head.

    Definetally reinstall the 02 sensors. Weld the bung into the header collector. Its the best place for it. You need all 4 cylinders to flow passed the sensor but want it as close to the heat as possible.

    Where did this guy go to get headers installed? Wherever it was, NEVER EVER EVER go there for ANYTHING. A place that finds it alright to just throw away your parts(the law states that ANYTHING removed from a car is the property of the owner) and toss it is bull, let alone removing such a CRITICAL part as the 02 sensor.
     
  5. 85burbanator

    85burbanator 1/2 ton status

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    my thorley tri-y headers came with a whole for the o2 sensor in it. i just put a plug in there since the burban is carbed and doesnt need the sensor. did they install the right headers?
     
  6. sled_dog

    sled_dog 1 ton status

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    they don't look like tri-ys. Never seen a set of black Thorley Tri-Ys. Thorley does make other headers though.
     
  7. Jonny-K5

    Jonny-K5 1/2 ton status

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    also didnt install a heat riser from header to air cleaner.
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    That woudl have required INSTALLING something, not cutting it off! :)
     
  9. K5MONSTERCHEV

    K5MONSTERCHEV 1/2 ton status

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    Those are thorleys. Just beat to crap, lol.

    How was this thing running with no O2 or MAP?!?!

    Your air cleaner setup also robs power, like Johnny said.
     
  10. Wingnutt

    Wingnutt 1/2 ton status

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    The main reason that its running like crap is because the computer isn't recieving signals from the MAP or the O2 sensor. Since it can't see the signals, it reverts to the "limp home" mode. And as you can tell, when it says limp home it means limp. :grin:

    Hook the MAP back up then get a better set of headers with the bung in the correct position or put a bung in the collector of the ones that are on it now and get yerself a 3 wire (heated) O2 sensor. The heated verson will help make up for the distance from the engine.
     
  11. AudioMaster

    AudioMaster Registered Member

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    First, thanks for all the advice. You guys just plain rock.

    Second, don't worry I'm NEVER going to the shop that screwed this thing up. I talked some more to the old owner today, he gets livid just talking about it.

    Third, I have a MAP sensor, it'll go in this weekend (thank heavens for my carburated '85 daily driver). Now lets talk 02 sensor, it seems the concensus is to weld a bung into the collector, sounds like that is what I'll do.
    Wingnutt, where do I get a 3 wire 02 sensor? Will my local parts store know what that is? Second where is the best place for me to get a bung for the 02 sensor (I am so busy right now I haven't even had a chance to call around . . . ) I'll try and locate the wire for the 02 sensor so I can be ready to rumble.
     
  12. AudioMaster

    AudioMaster Registered Member

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    I found a weld in 02 sensor fitting from Jegs part number 555-30740, for those who may need one in the future.
     
  13. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Turbo city can sort you out with a bung and a 3 wire o2 sensor. Just cut a hole in your collector and weld the bung in. Wire up your map and connect it to manifold vaccum source and you'll be sorted! Oh, and turn that bloody air cleaner lid over and get a proper hose to take it to the cold air source! :)
     
  14. Thunder

    Thunder 3/4 ton status

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    Before you go buying a MAP sensor post up a pic of the right side of the throttle body with the air cleaner removed. I cant see from your pics because the air cleaner is in the way But your map sensor may still be there.
    There are 3 black boxes on the pass side of the TB from front to back they are :
    1 A square box with 4 wires is the ETC module it works with the knock sensor to controll timing.
    2. Under the ETC and a little further back is the EGR controll solonoid it has 2 wires and a vaccum tube. It controlls EGR operation
    3. Next is the MAP sensor. It has 3 wires and a vaccum tube. It is needed to control timing and fuel curve.

    If you post a pic we can tell you exactly what has been hacked off.
     
  15. y5mgisi

    y5mgisi 1 ton status

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    It looks like there is a pluged vac. line that would have gone to the egr solenoid(sp?) or the map. right above the pass valve cover.
     
  16. Mad-Dog

    Mad-Dog 1/2 ton status

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    The MAP or (Manifold Absolute Pressure) sensor can be mounted anywhere inside the engine compartment so long as the it is connected to the ECM and maifold vacuum.
    The O2 sensor should be mounted in the collector on either side (makes no difference).
    You can install a non-heated sensor (1-wire) or a heated sensor (3-wire), the choice is yours and you may notice a improvement in driveability with the heated sensor....maybe.
    Heated sensors such as a Bosch unit have 3 wires (2 whites and a black),
    the black wire is signal (readable in millivolts using a high-impedance voltmeter), and the 2 white wires are power and ground, does not matter which wire goes where as the heater does not care as long as 1 is connected to power and the other is connected to ground.
     

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