Question about 1999 GMC Jimmy

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MAF Sensor and 02 Sensor

Is there a way to test the MAF and 02 Sensors on a 1999 GMC Jimmy?

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  • debbielegal1 Jan 25, 2009

    The check engine light is not on and never has been. I have had the vehicle in the shop 4 times. It is not the transmission, we replaced the fuel pump, fuel filters, catalytic converter, gave it a complete tune up. Some have suggested it might be either the MAF Sensor or 02 Sensor but it is getting very expensive to "try" different things and the computers can't find anything.

  • debbielegal1 Jan 25, 2009

    It starts and runs fine but it won't get out of its own way. You get to 20-30 mph and it bogs down and stalls out. It's very frustrating making a car payment on a vehicle that won't go anywhere.

  • debbielegal1 Jan 25, 2009

    They tell me it is not missing but the first impression is that its not getting any fuel. They checked the fuel pressure regulator and it reads 55-60 psi,

  • debbielegal1 Jan 25, 2009

    It doesn't sputter, just bogs out.

  • debbielegal1 Jan 25, 2009

    We've checked the timing, replaced the air filter, we can't get to Auto Zone - it won't stay running that long and won't go over 30 mph and we have tried fuel injector cleaner.

  • debbielegal1 Jan 25, 2009

    No vacuum leaks, no exhaust smoke. We had a transmission specialist check the transmission. They rebuilt the starter and replaced the shift selenoids, installed a filter kit, fluid and conditioner, drained and flushed the torque converter, oil cooler and lines. We had it at another shop that changed the crankshaft sensor and repaired the wiring connection on the ignition core.

  • debbielegal1 Jan 25, 2009

    What trouble codes?

  • debbielegal1 Jan 25, 2009

    Thanks. The only thing we haven't replaced is the MAF sensor and the 02 sensors but that's another $300 to "try". They are $300ing me to death.

  • debbielegal1 Jan 25, 2009

    I had it at a dealer once a while back, they couldn't find anything either except for a bunch of expensive "maybes"

  • debbielegal1 Jan 25, 2009

    We have replaced all of the plugs. It doesn't have anything to do with fuel economy - it doesn' run. It won't get out of its own way. We've checked all of the hoses. Like I said, this has been going on for 2 years.

  • debbielegal1 Jan 25, 2009

    We've replaced the fuel filters and the catalytic converter.

  • debbielegal1 Jan 25, 2009

    We've replaced the fuel filters and catalytic converter.

  • debbielegal1 Jan 25, 2009

    We have replaced the fuel filters and catalytic converter.

  • debbielegal1 Jan 25, 2009

    We've replaced the fuel filters, put a new fuel pump in, and replaced the catalytic converter.

  • debbielegal1 Jan 25, 2009

    We replaced the fuel pump with a new one, not after market. We've also replace the catalytic converter and the everything else. Still does the same thing.

  • lizzyandme Apr 28, 2009

    My jimmy was stalling out after 25 miles per hour.... turned out my brakes were stuck in the on position...anti lock brakes.... it wasn't until the car would stay still without brakes at red lights that the problem was solved. I also replaced the transmission... right before.... now my car just stalls whenever I start it...then I turn key again and it is fine. sometimes it goes into tow haul automatically. I'm not impressed with GMC.

  • Roberta Smith
    Roberta Smith May 11, 2010

    What are the symptoms of a bad oxygen sensor?
    The biggest indicator of a faulty oxygen sensor is a noticeable decrease in fuel economy, along with a rich mixture. Now, this does not automatically indicate that the sensor has failed. Be sure to check all vacuum hoses for leaks as well as the ignition system, check the plugs, (are they fouled?) check the rotor, distributor cap, points, spark plug leads, and condenser (check all of these where applicable) Vacuum leaks and ignition problems are notorious for causing fuel economy problems. It’s a good idea to inspect and re-new the vacuum hoses every couple of years anyway. Other symptoms of a faulty sensor are a loss of power, (particularly when accelerating from a stand-still), overheating, and spark plug fouling, both of these are due to an increased rich or lean running condition.

    The more i read that the more i'm leaning toward an o2 sensor... but lets wait till church is done (*cough*) for the other experts i've left a message for to show up

  • William Aten May 11, 2010

    A dealer or mechanic and even some part stores such as Auto Zone have diagnostic machines that read trouble codes from your computer narrowing down your search for the problem.

  • Roberta Smith
    Roberta Smith May 11, 2010

    just curious.... have you been taking it to a dealer ?

  • Roberta Smith
    Roberta Smith May 11, 2010

    I'll get some of my friends here that i trust to read this over and give advice.... seems you have repaced everything and i'll not suggest that you replace other parts till we have an idea exactly what it is.



    Robert

  • William Aten May 11, 2010

    Well if you can't get to an Auto Zone you need to find a machanic shop to read trouble codes for you.



  • Roberta Smith
    Roberta Smith May 11, 2010

    who ruled out the transmission.... and i am looking for the voltages you should get on the maf.... two more things... what colour is the exhaust smoke and do you hear any vacuum leaks at all ?

  • Roberta Smith
    Roberta Smith May 11, 2010

    a few things ... almost sounds like timing issues.... but i'm not going to suggest any wallet fixes yet. first check your air filter to make sure it's not clogged up with dirt.... second whip down to autozone and buy some injector cleaner (reasonably inexpensive and may fix the issue). and i'll hunt around for the manual and see if i can find the test for the maf.... oh one other thing... inspect all the duct work to make sure nothing is off from the breather to the motor... including any loose wires your mechanics may have forgot to hook back up.



    Robert

  • Roberta Smith
    Roberta Smith May 11, 2010

    I'm presuming that is within range... or they would have had you replace something else.... i mean when you are driving it... other then it feels like it can't get out of it's own way... does it **** or sputters sometimes ?

  • Roberta Smith
    Roberta Smith May 11, 2010

    any miss or just "appears" to be starving for fuel ?



  • Roberta Smith
    Roberta Smith May 11, 2010

    troubleshooting with your wallet is expensive... what's the problem you are having ?



    Robert



  • Roberta Smith
    Roberta Smith May 11, 2010

    if the check engine light is on ... drop into autozone and have them read the codes for you....



    Robert

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Replace the fuel pump with another one.
This is a common issue.
Don't use an "aftermarket" pump; buy one from Chevy.
I just had this exact same issue in my shop. The truck would run for a bit, and then just stop. I had the truck towed in, and the fuel pressure was good. Drove it for a while, with the gauge hooked up and taped to the windshield, I could see the fuel pressure start to drop off. I told the owner that she needed a new fuel pump.
The owner told me that the pump was 2 months old. I went ahead and changed it anyway. A new fuel pump cured the problem.

Testing the MAF and the O2s is not going to tell you anything. A failure, an open or a short would set the check engine light.
Please feel free to get back to me if you desire any further input. Thanks for choosing FixYa for assistance.

Posted on Jan 25, 2009

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You've mentioned the plugs. How was the plugs? I just replaced all of my oxygen sensors last week because I was kind of having the same problem with my 99 GMC Jimmy. My Jimmy is running just fine now after I replaced all of my oxygen sensors. I bought them from O'Reilly for $52.99 a piece, AutoZone was selling it for $59.99 a piece. I had to disconnect the battery for a few minutes after I installed my new sensors. All is cool now.

Posted on Apr 28, 2009

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For it to bog down and have no exhaust fuem leads me to believe it is getting a lack of fuel. I know you said the fuel pump is putting out enough and something about the MAF (Mass Air Flow Sensor) and the O2 (Oxygen sensor) but to tell the truth, it maybe getting those signals because the circuit in question is so far below level that those two look too much. If I'm not mistaken there is a pressure regulator between the fuel line and the injectors. This device could be clogging or almost sticking shut. Any help here? If this is helpful, please post as such. TY

Posted on Jan 27, 2009

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Does it idle fine? just bogs out driving? if fuel filter is clogged it would show good pressure but would not have the volume to keep up under load need a gauge on it while driving. also if cat convertor is stopped up it would bog out. this would be indicated by convertor getting extremely hot. there is really no quick fix guidde i can give you need to be able to see data while it is acting up. I doubt it is o2 sensor. check your maf for trash in it.

Posted on Jan 25, 2009

  • TripleTauto
    TripleTauto Jan 25, 2009

    it will be almost impossible to guess the problem without seeing the sensor data computer is seeing. my advice would be to ask around about a good shop that does driveability work and have it looked at.I understand you have had it at several shops put you have not had it at a good one yet it seems. autozone will not be able to help you all they can do is read codes and dont know what half of them are that they read. if you explain to me a little better what it is doing i will continue to try and help you. idles fine ? revs up fine? wont o past 30? after warms up? all the time?

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The distributer is bad the gears on the end are wore down to a point that what makes it bog lack of spark. its actually flooding out ... been there done that.....

Posted on Mar 02, 2010

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