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87 surging at idol and CEL on, but no codes in computer.....

Discussion in 'The Garage' started by Batmanjr, Apr 23, 2003.

  1. Batmanjr

    Batmanjr 1/2 ton status

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    I finally got the ol beast timed cause the muffler shop finally put the exhaust on.... ANyways, When I tore this truck apart and changed the gauges cause they were broke, I noticed the previous owner had conveniantly unplugged the CEL.... I plugged the bulb back in, and now that the truck is timed and the ECM was cleared, I start the truck and the darn thing stays on at a low glow.... I mean low glow cause when I check the codes, the light never really goes off, just gets brighter slightly and then low glow and then bright has it flashes code 12 at me constantly.... The only code in it is code 12..... SO now what.... I just rebuilt the engine, new sensors all over, new TBI(Holly), new cap and Rotor(MSD), new coil(MSD), new intake, no egr valve, no smog, no knock sensor, and the engine seems to surge as it idols and when I stick it in gear, it boogs way down and sometimes dies... IDEAS? Thanks all! /forums/images/graemlins/thumb.gif
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    First thing I'd do is pull the gauges, and figure out which wire is the "lamp driver" wire. You need to check it for voltage. Sounds to me like either there is a ground problem, or a problem with the printed circuit board. The light should either be on or off obviously, not dimly lit.

    Since the bulb gets bright when the ECM "commands" it too, it sounds like the ECM side is working correctly, and that would lead me to believe the gauge cluster is a more likely culprit. The copper "bands" tend to get mixed up where the plug connects to the cluster.
     
  3. 90K5

    90K5 1/2 ton status

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    check for vacuum leaks, sounds kinda like one.
     
  4. woody9

    woody9 1/2 ton status

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    my 91 was doing that idle surge too, and no code. I was thinking the idle control. Finally started to get the SES light, and it was a 22 (TPS). Popped a new one on, adjusted a tad, and light went away. so did surging!
    Confirm your vac & check grounds too!
     
  5. Thunder

    Thunder 3/4 ton status

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    You really need all the sensors and EGR hooked up for the ECM to function properly. The ECM tests the EGR while driving.It uses the MAP sensor to look for a drop in vacume when the EGR valve is opened. It also looks for a response from the knock sensor.
    The EGR is important to a FId vehicle. It is needed to reduce combustion temps so the engine can run more timing advance. Disconnecting the EGR only hurts performance in a computer controled engine.
    If it doesn't get a responce from the knock sensor the ECM may not advance timing.
    When it doesn't have input from the sensors/controls you removed. It will usually go into bypass or Limp home mode. The engine wont run very well in bypass mode.
    The ECM may also be bad.
    It is very hard to diagnose problems when you are missing needed sensors and controls.
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Yeah, I guess with missing sensors (now that I read to the bottom of the message : ), only thing a correctly working SES light is going to do is tell you that you can't run TBI correctly without those sensors, knock at least.
     

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