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  1. #1

    Default 1998 GMC Sierra 2500HD won't pass emissions

    The truck was bought used.
    The mechanic says that all 3 Oxygen sensors need to be replaced.
    He said the test indicates that there might be fuel in exhaust.
    I indicated that I suspect there is occasional misfire (especially under load).
    Is it any worth replacing all oxygen sensors? Should we focus on spark plugs/reason for the misfire?
    The oxygen sensors alone will set me back some $500 including parts and labor.

  2. #2

    Default

    Well O2 sensors I think are like $80 a piece and are really easy to put in...and if im not mistaken i think you should have 4. Spark plugs are never a bad idea especially if it has a lot of miles on it. The distributor cap and rotor would also be a good upgrade.
    2000 Chevy Silverado 4WD Classic
    2'' lift Torsion Keys and air shocks
    33/12.50 Hankook Dynapro M/T
    3 1/2'' down pipe back 6" Tip
    Dodge Towing Mirrors
    Smoked Tails, Cab Lights, and Side Marker Lights
    1% Rear and Side Window, 20% Front Tint
    American Racing Wheels/ With a custom black paint
    Cold Air Intake
    Edge Performance Chip
    Custom Audio System
    LED Tails
    Black background headlights and parking lights

  3. #3

    Default

    Quote Originally Posted by MTM View Post
    Well O2 sensors I think are like $80 a piece and are really easy to put in...and if im not mistaken i think you should have 4. Spark plugs are never a bad idea especially if it has a lot of miles on it. The distributor cap and rotor would also be a good upgrade.
    Shouldn't there be a logical sequence of tests to narrow down what's busted, instead of replacing everything?

  4. #4

    Default

    If there is a missfire the o2 sensors are going to get the wrong readings. The missfire has to be fixed before you just go replace o2 sensors. You will still have the same problem

    Mud Truck
    1984 Chevy K5 Blazer
    -454 Edelbrock V8
    -33" BFG Mud Tires

    Daily Driver
    2006 Chevy Silverado K1500 LT Z71 - 5.3 V8
    -Bull Bar
    -Step Bars
    -Flowmaster 40 with dual tailpipes
    -Smoked Tails

  5. #5

    Default

    It is likely that it is the o2 sensors... Why? Because you had the local wrench look at it and diagnose it. He had the truck and presumably the tools and skills to troubleshoot it. Why are you hesitant to accept his diagnosis? Does he seem incompetent? If he is correct and you don't want to fix it because of the cost of the parts, then you can throw parts at it all day and change nothing, which means that in the end, you are going to pay a lot more to have it fixed.

    There could be a LOT of other things causing the issue. you really didn't give us enough information to pinpoint anything. Is the service engine light on? If so, what are the codes? If not, are there any stored codes that might give a clue? Does it misfire when it is hot? cold? all the time? only under load? Why does the wrench at the shop think o2 sensors? Are you losing any coolant? If so, it could be an intake gasket. those are notorious for leaking. Could be bad plugs, wires, cap, button, distributor, ignition control module, injector, fuel pressure regulator, vacuum leak, Bad cats, Mass airflow sensor, coolant temp sensor, MAP sensor... any number of things or combinations of things can cause that... Of course, it could actually be the o2 sensors.

    Start with the basics: read the computer and report every little detail that you can think of. read the data stream from your sensors. How many miles does the engine have on it? What KIND of plug wires are on there? What KIND of plugs does it have installed? What ARE the symptoms?
    Last edited by moogvo; 04-17-2012 at 09:45 AM.
    "It went together didn't it? Well then there has to be a way to take it apart!" - Me.

    Check out my image gallery HERE.



    "The true measure of a man is how he treats someone who can do him absolutely no good." ~Samuel Johnson (1709-1784)

  6. #6

    Default

    ^^^^^^^^^Totally agree
    2000 Chevy Silverado 4WD Classic
    2'' lift Torsion Keys and air shocks
    33/12.50 Hankook Dynapro M/T
    3 1/2'' down pipe back 6" Tip
    Dodge Towing Mirrors
    Smoked Tails, Cab Lights, and Side Marker Lights
    1% Rear and Side Window, 20% Front Tint
    American Racing Wheels/ With a custom black paint
    Cold Air Intake
    Edge Performance Chip
    Custom Audio System
    LED Tails
    Black background headlights and parking lights

  7. #7

    Default

    Don't you think it's unlikely that all 3 (or 4) oxygen censors are dead?

    From what I recall, the computer indicated that only one is dead.

    While I don't think the mechanic is incompetent, I'd like to follow a process of elimination where I don't replace all parts to determine which one actually needed being replaced. I don't mind spending the money, as long as it fixes the problem.

    The engine is 5.7 and it has 125K miles on it.
    The misfire to me seems to happen only under load, but the emissions test indicates otherwise. Meaning, you probably just don't feel when it misfires on idle in a V8, while the loss of power is felt when you're in low RPMs.

    It's a stick shift, if it helps
    Last edited by NetComrade; 04-17-2012 at 10:36 AM.

  8. #8

    Default

    Mine had a similar problem where it threw a code and it was for the two O2 sensor upstream from the cat. i spent the money and bought all 4 while i was under the truck figure id do all of them. I had a power issue also where on start up it would lug down when i was ready to take off. So i started with the distributor cap and rotor. Didn't fix it,so then it threw the code for O2 sensor fixed those still did it so then i did plugs and wires. It was better but still wasn't 100%. Then i figured out that my intake gaskets where pretty much gone on one side so i went ahead and replaced that...seemed to fix it. It runs great now after all that a chip, exhaust, and intake i average about 15-17 on the highway and has tons of power
    2000 Chevy Silverado 4WD Classic
    2'' lift Torsion Keys and air shocks
    33/12.50 Hankook Dynapro M/T
    3 1/2'' down pipe back 6" Tip
    Dodge Towing Mirrors
    Smoked Tails, Cab Lights, and Side Marker Lights
    1% Rear and Side Window, 20% Front Tint
    American Racing Wheels/ With a custom black paint
    Cold Air Intake
    Edge Performance Chip
    Custom Audio System
    LED Tails
    Black background headlights and parking lights

  9. #9

    Default

    Quote Originally Posted by NetComrade View Post
    Don't you think it's unlikely that all 3 (or 4) oxygen censors are dead?

    From what I recall, the computer indicated that only one is dead.

    While I don't think the mechanic is incompetent, I'd like to follow a process of elimination where I don't replace all parts to determine which one actually needed being replaced. I don't mind spending the money, as long as it fixes the problem.
    I wasn't implying that you were being cheap, but YES! They can all go out at the same time. You run the wrong additive or cleaner through the engine and you can kill them all in one swoop! So it CAN happen! If the computer says only one is bad, start there!

    Before anyone on a forum can help you (which is difficult at times even with a lot of information), you will have to give us more than "The wrench told me bad o2 sensors, Sometimes it misfires I think. What else can it be?" (paraphrased). We need much more information to be able to help you out. a great place to start would be to go back to the tech and ask questions. Get as much information as you can. Get him to show you the readings on the scan tool. gather as much info as you can. Maybe take it to another shop and get a second opinion. More is better in this instance.

    "Process of elimination"... That means that you will throw plugs and wires on it. nope, that didn't fix it. Fuel pressure regulator. Nope. Intake gasket. Nope... On and on until you are pulling your hair out because your problems didn't go away. We had a car in the shop the other day... a 1994 Suburban. Check engine light would come on at highway speeds but then go back out when you shut it off. The complaint was that there was a hesitation on acceleration. We told him that it was pulling an EGR code. He decided that the EGR wouldn't fix his problem (Because he "checked" it). He told us "No, I took it off and cleaned it. It opens and closes like it should and it holds open fine under vacuum.", so he put plugs, wires, cap, button and about $300.00 of other parts on it. It came back with the problem. We put an EGR on it and the problem was gone. Turns out that the spring in the EGR was weak and the pressure from the exhaust was pushing it open when the computer wanted it closed. This happens all the time! That's why there are diagnostic connectors on them. No, the diagnostics won't tell you exactly what the problem is, but they are clues to help you solve the puzzle by getting you pointed in the right direction.
    The wrench told you o2 sensors. It is a pretty good bet that the o2 sensors would be a good starting point - UNLESS he was taking a guess at why you didn't pass inspection and didn't actually scan it. At that point, you need to have it scanned for codes at the very least!

    In any case, have it checked out and bring the information back here and we can try to help you. I really don't like to "speculate" to someone who then goes out and buys parts and then comes back in here upset because my advice didn't work.
    Last edited by moogvo; 04-17-2012 at 12:42 PM.
    "It went together didn't it? Well then there has to be a way to take it apart!" - Me.

    Check out my image gallery HERE.



    "The true measure of a man is how he treats someone who can do him absolutely no good." ~Samuel Johnson (1709-1784)

  10. #10

    Default

    Just a quick question. A friend has a power issue where it runs great a easy throttle but as soon as you give it gas to where it tries to hit the passing gear it bogs down. It has had all the plugs done, wires, cap and rotor and all the pressures are good.But just wont throw a code and theres no previous codes that lead to anything. Think this could be a sign of a bad EGR?
    2000 Chevy Silverado 4WD Classic
    2'' lift Torsion Keys and air shocks
    33/12.50 Hankook Dynapro M/T
    3 1/2'' down pipe back 6" Tip
    Dodge Towing Mirrors
    Smoked Tails, Cab Lights, and Side Marker Lights
    1% Rear and Side Window, 20% Front Tint
    American Racing Wheels/ With a custom black paint
    Cold Air Intake
    Edge Performance Chip
    Custom Audio System
    LED Tails
    Black background headlights and parking lights

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