Need Help With Check Engine LIght

Discussion in 'GM Powertrain' started by Jaystahoe, Jul 14, 2007.

  1. Jaystahoe

    Jaystahoe New Member

    I have a 99 tahoe LT , Truck has a slight miss at an idle in cylinders 3&4,As soon as you get above 1000 rpms the truck is fine it's not bucking,or missing causing it to run like crap when driving it down the road, i have replaced the o2 sensor that was bad ,and egr valve gasket with the new updated gasket w/ screen, Me and a couple of my techs are thinking Metering body assy, Does not have any intake leaks also tested for that last week, Is there anything else it could be just wondering this is my first chevy SUV
  2. 84fiero123

    84fiero123 Epic Member 5+ Years 1000 Posts Platinum Contributor

    Check to make sure that all the plug wires are snaped on tight. I had this problem and is was a loose plug wire. Not so loose it fell off the boot, but loose enough to give it a skip at low idle.

    Pull the boot up the wire and put the little snap collar on the plug then push the boot down. That way you are sure it is seated right.
  3. Jaystahoe

    Jaystahoe New Member

    ok i'll give that a shot , oh yeah i also did the cap,rotor,plugs and wires
  4. Dj Friction

    Dj Friction Rockstar 100 Posts

    My exact thought....becuase I had the same problem once....The spark was jumping the gap in the plug wire first......I found it when it dicolored the plug wire cap....

    Try it it will not hurt....
  5. HDDP

    HDDP New Member

    Good Thread / Info

    I bought a '98 K2500 7.4L Burb at an auction for $4k a few weeks ago that had been mechanically neglected for most of it's 110k life and I'm in the process of slowly-but-surely getting it back into fighting shape...

    One of the first things was to replace plugs and wires. But since, I have had a random misfire... My diagnostic software is aftermarket and doesn't isolate cylinders, but is showing a pending DTC "random misfire" I have reseated the wires and still happening... Funny, it didn't misfire with the old worn plugs and wires :lol: Too bad I threw them away...
  6. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Wait until dark and open the hood while its running, a lot of times you'll see the spark jumping.
    I diagnosed a friends Chevy truck for this problem a few weeks ago without lifting the hood. The arc was so bright you could see it in the reflection of a puddle of rainwater under the truck.
  7. 84fiero123

    84fiero123 Epic Member 5+ Years 1000 Posts Platinum Contributor

    You could have the same problem, or a defective plug or wire.

    A spark tester can be put in between the individual plugs, at the plug and the cap. It could help you track down where the problem is. They have a window in them that shows the spark, are adjustable for the size of the gap too so you can get one, and use it on any vehicle.

    Could also be a defective cap or rotor. Check the cap and rotor first.
    Last edited: Jul 14, 2007
  8. dwill3015

    dwill3015 Epic Member 5+ Years ROTM Winner 1000 Posts

    My wife's Burban had a problem with running rough and jumpy at low RPM's and I tried new plugs and wires, even a fuel filter and still acted the same so I took it to dealer and they found a bad coil pack.
  9. HDDP

    HDDP New Member

    Thank you for your expertise... This truck is going to take quite a bit of TLC to get it back to where it should be... I will spend much time picking the grey matter of the wonderful forum members here...

    Funny thing is that I purchased this suburban to tow my race car to the track... now it's become a pet project to get into perfect operating condition... And taking more time than my race car...

    Since I can't upload large files to this site, And a video from some recent testing... :great:
  10. 84fiero123

    84fiero123 Epic Member 5+ Years 1000 Posts Platinum Contributor

    I forgot all about that, coil packs. Does this year have a distributor or a coil pack?

    The spark plug tester can be used on the coil packs to. I took a fuel injection course a few years ago at the local high school for adults and the guy was like me.


    And gave us all sorts of handy little tricks to test high tech electronic ignition and fuel injection systems.

    The nice thing about the spark plug tester is you can use them in line so you can run the vehicle while testing.

    He used 8 on a coil pack to show us how to find an intermittent spark loss. But also said it can be done with just one.

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