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More Check Engine light ???

Discussion in '80-Series Tech' started by Jomama, Aug 19, 2003.

  1. Jomama

    Jomama

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    So C.E. light went on this weekend. Its gonna be a week or so until I could really deal with it. However in reading thru the archives, I thought it might be worthwhile to disconnect the battery for 5 min to try and reset the light. Curious if it'll come on again. Light went out after I reconnected battery.

    But now the cold start/high rev-idle mechanism doesn't appear to be working. It was quite cool this morning, and I was very suprised when starting the truck to have the rpm drop WAY down when I started it. What would disconnecting the bat have to do with this ???
    Any thoughts?

    Thanks all
     
  2. Gumby

    Gumby Supamod Staff Member s-Moderator

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    The computer remembers certain information about your truck. When you disconnect the battery you reset that info. Try it for a couple days and see if your origonal running conditions come back. Also try to enable some "drive cycles". This is when you drive for long enough to let certain criteria happen. Varied driving including sustained highway speeds are neccesary. Your light might be a two drive cycle problem.
     
  3. landtank

    landtank SILVER Star

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    That's what i did. Reset the light last night. Did 2 40 mile drives today with both mixed and some highway. Light has remained off. I just put on a Borla exhaust and nearing a tune up so between aged ignition parts and the computer learning a free flow exhaust I'm hoping for a one time incident.

    Just wish I new what code it did through :(.
     
  4. cruiserdan

    cruiserdan SupportingVendor Emeritus Supporting Vendor Moderator

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    When you kill the memory power to the ECM the IAC looses it's mind for a time, that is why your idle is off. It will take up to 10 or 15 start cycles for the IAC to re-set.

    Try this:

    Start the engine and let it warm up. You may see an abnormally low hot idle. Shut the engine off and re-start after about 20 seconds. You should see the idle creep up slightly. shut the engine off and repeat. Each cycle wil raise the idle slightly until it's where it belongs. :D

    Pretty scary, huh? :flipoff2:

    Footnote:

    If your battery dies and you get a jump, the hot idle will probably be too low. I had this happen once and I had to keep me foot on the gas pedal so the old gal wouldn't die at the stop lights on my way to work because I knew if she did I was toast. When I got to work I shut her down and lo and behold, not enough juice in the battery for a re-start. :eek:
     
  5. Jomama

    Jomama

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    Check engine light came on two weeks ago. Reset light right away to see if it'd come back on. Came back on Sat morning as I headed out to raft a river. Picked up a little code reader thing, plugged it in and read the flashing C.E. light to be (2pulses-space-8pulses), FSM indicates this is code 28, #2 Oxy sensor. No problem. Spent the rest of Sunday and monday doing some basic maintenance, greased zerks, oil change, and flushed/cleaned and filled the cooling system. Check engine light was on thru all the running of the engine during the cooling flush.

    Now today I started the truck and have driven it around for a bit and NO CHECK ENGINE light???? What gives. I did NOT disconnect the battery or pull any fuses over the weekend. Is this thing just possessed?
    :-\
     
  6. Gumby

    Gumby Supamod Staff Member s-Moderator

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    The O2 sensor codes are probably soft codes. The computer sees a problem of a sensor out of range. If the problem doesn't repeat, it shuts the light off. You probably have the code stored in the computer for a bunch of drive cycles, then it will go away as well.
    You seem to have either a rear o2 going bad or cat going bad.
     
  7. cruiserdan

    cruiserdan SupportingVendor Emeritus Supporting Vendor Moderator

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    Are you sure that that is the only code stored. Sometimes on 93's I see a 21 or 28 and an 83,84,85 which are TCM to ECM communication issues. Short T1 and TE1 and check the code(s) again. You probably need O2 sensors (89465-60110, comes in a pair) If you have the 83,84,85 you will need to replace the engine ECU....$ :eek:$ I speak from first hand experience on that one :'( .


    Dan.
     
  8. Jomama

    Jomama

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    [quote author=cruiserdan link=board=2;threadid=4442;start=msg37297#msg37297 date=1062545521]
    Jo,

    Are you sure that that is the only code stored......

    [/quote]

    I let it cycle thru the codes a few times if thats what you mean? Each time it only went thru the 2flash-pause-8flashes, and restarted the same pattern. According to the FSM it should have displayed all the codes in succession if there was more than one code stored (and then started the whole string over again).

    Now I'm interested in plugging the codereader widget in again and seeing if I get a output on the C.E. light.
     
  9. landtank

    landtank SILVER Star

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    2 weeks after I reset my ECM the CE lkight came back on. Went down to AutoZone and the code is a P0136. So this past Saturday I did a full tune up and reset the code. Quite abit of driving Sun. and Monday with no light. My Autoeginuity scanner should be in when I get back so I can start following along with the manual and run those tests.
     
  10. cruiserdan

    cruiserdan SupportingVendor Emeritus Supporting Vendor Moderator

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    Good, the 83,84,85 is a pain in the a$$.