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'98 Obd Ii

Discussion in 'The Garage' started by SUBFAN, Jul 2, 2005.

  1. SUBFAN

    SUBFAN 1/2 ton status

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    Olds Bravada....Running like dog crap....

    The computer says cylinder misfire, random. This is on all cylinders. The obvious fix is new plugs, wires.

    It does not make sense to me that all plugs went bad at the same time. What else to check into? The coil? Is there an ignition module or pick-up coil to check?

    I don't know a lot about this newer stuff, thanks in advance....
     
  2. gone huntin

    gone huntin 1/2 ton status Premium Member

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    I don't know what year they changed to the plastic distributors on them but I have replaced several of them and electric egr valves for this problem. My first bet would be the distributor though.
     
  3. sled_dog

    sled_dog 1 ton status

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    Its most likely not all the cylinders. THe way the rules of OBDII break down states that if there is a random misfire on more then one cylinder, it just has to tell you there is a random misfire and let you figure out where it is. There are a bunch of things that could be causing a misfire(down to bad fuel injection and fuel pressure). THe fuel pressure thing could cause a misfire on all cylinders really. Do you have the ability to watch datastreams and determine what cylinder is misfiring?(may require a good scan tool). If its about time for a tune up anyway, wires would be a good start. But I'd pull all the plugs and check for spark(with a spark tester, not the spark plug, just the plug puts little load on the ignition system to accurately test it).

    There won't be a pickup coil to check but there is an IC Module. How to test it on that :dunno: Could be something like a crank position sensor also. If you have the ability, look if there are any pending codes. The Misfire code may have interuppted the crank position sensor test, though I doubt it since the crank position is what is used to determine there IS a misfire.
     
  4. SUBFAN

    SUBFAN 1/2 ton status

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    I replaced all the plugs, wires, and did the cap and rotor. It seemed to fix the problem, but this was only temporary.

    Upon start up, it will seem to only run on two cylinders, with starting difficult.

    After you get it running, it will run just fine at all levels.... :dunno: :dunno: :dunno: :dunno:

    Two weeks ago I replaced the fuel pump....Does this have any connection?
     
  5. LongIslander26

    LongIslander26 1/2 ton status

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    Misfires

    Leaking intake manifold gaskets can cause random misfires. Have you been able to pull any DTC Codes? Are you getting any lean codes?(P0171,P0174,P0300) GM has had problems with intake gaskets, ecpecially on the Vortec motors. May want to check your fuel pressure, and for vaccuum leaks behind the MAF as well.
     
  6. K5MONSTERCHEV

    K5MONSTERCHEV 1/2 ton status

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    DO you have any specific codeS?
     
  7. SUBFAN

    SUBFAN 1/2 ton status

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    It gave us a PO 300, random misfire....

    I always blame the computer with being the trouble when equipped. I tend to forget about the basic things like vaccum leaks and such.... :doah:
     
  8. sled_dog

    sled_dog 1 ton status

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    computer controlled vehicles aren't difficult to work on when you bother to learn a little about them. Not trying to say anything about you. I used to think the problem is always the computer too but it so often ends up being something simple that you've seen on a carbed vehicle.
     
  9. SUBFAN

    SUBFAN 1/2 ton status

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    Yeah well, I need someone to put that computer crap into English I can understand....Guess I will have to break down and learn a bit....

    The most recent code was PO 302, cylinder #2 misfire....But why only the problem with start-up?????
     
  10. LongIslander26

    LongIslander26 1/2 ton status

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    Start up problems

    I've seen it happen that as the engine warms up and things start to expand, the leak sort of seals itself. It may just be loose intake bolts. Put a ratchet to some of the intake bolts and see if they're loose. I'm not saying that this is 100% your problem , I've just seen it alot on Vortec motors. Plus, when the engine is idling, that's when vaccuum is the highest because the throttle plates are closed, and the leak throws the air/fuel ratio out of whack. Just keep in mind that GM only calls for 11 lb/ft of torque on the intake bolts, so if they ARE loose, then you'll need to clean them up and use some red Loc-tite on them when you reinstall them. Let us know what you find. DTC code P0171 is "system lean bank one",(Drivers side), P0174,"system lean bank 2" (Pass side) You can also try the spray carb cleaner around the gaskets trick when the engine is cold, and see if the rpm's climb.
     

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