1997 k1500 misfires like Grande when hot PLEASE HELP

Discussion in 'Engine Performance + Maintenance' started by 97 bowtie, Feb 12, 2020.

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  1. 97 bowtie

    97 bowtie Newbie

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    Hello all, I’m new to the forum but not new to the gmt400. I’ve had my truck five plus years and loved every minute of it even though a lot of those minutes have been painful.

    So my current situation is my truck has 180k miles on it, in the past few years it’s gotten intake gaskets, new spider injection, new fuel pump, new msd distributor, new coil, new exhaust including headers and 02 sensors. It just got a new crank sensor flexplate and starter.

    it was also timed properly with a scanner and is within 1deg on the cam retard so the timing is dam near perfect.

    Last week it threw a p300 code and was barley drivable but it got me from a to b. I figured the wires were getting heat soaked from the headers we put on it so I changed the wires for a set of new ones from msd, the same wires I’ve been running without a hiccup for two plus years in addition to that I put heat insulator boots over the plug boots to protect them from the heat of the headers. Needless to say the truck ran like a sewing machine cold after I installed the wires drove it around no problem got it up to temp.

    come out a half hour later she barley started and stalled when I shifted into gear. The one thing that was never changed and looked original was the ignition control module so I went ahead and changed that being it had 180k miles on it good possibility it was bad.

    now the issue remains, she runs mint and I mean she hums without skipping a beat when she is cold, as soon as it heats up forget about it, it feels and sounds like it wants to explode. I’m at a loss with this thing, I need it to get itself by for another year ish, then it’s getting a 5.3 lm7 swap that’s sitting in the garage waiting on the time
     
  2. Mark Gilbert

    Mark Gilbert OBS Enthusiast

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    I have heard of the coolant temp sensor causing a similar issue. It runs well in closed loop then never switches to closed loop and runs like crap. YOu've got an OBD2 vehicle, so you have the option of a cheap elm327 scanner and an app for your smartphone to give you live data. That will be more helpful than anything.
     
  3. 97 bowtie

    97 bowtie Newbie

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    That’s something I can look into next time I have the truck running I can plug the scanner in and see how that’s functioning,

    also forgot to mention it’s been throwing a p1351 code which is the ignition control module and or ignition control module harness voltage low. I replaced the module yesterday with a new Delphi part and had no change whatsoever
     
  4. texas tough

    texas tough OBS Enthusiast

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    the aluminum corrodes on the baseplate the module screws into are you SURE the module is seating 100 percent and grounding good? are the connectors that plug into the module TIGHT, CLEAN and none of the wires pinched or burned?
    what u are describing is CLASSIC for a module not making a good connection once warmed up,,
     
  5. 97 bowtie

    97 bowtie Newbie

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    When I replaced the icm I cleaned the aluminum heat sink front and back and it was in very good clean condition, used the thermal paste on the module and on the back of the heat sink that contacts the steel bracket that also holds the coil, I can take it back apart and take a wire brush to the steel bracket and ensure that’s squeaky clean as well but I did clean it all down with break cleaner and a rag before reassemble
     
  6. 97 bowtie

    97 bowtie Newbie

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    Wiring is the next thing I will start looking at, I did read on another site that a coolant sensor can cause a similar issue but it’s throwing a code for the icm so idk
     
  7. 97 bowtie

    97 bowtie Newbie

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    Ok so a little more info as I just drove the truck to the train station to go to work and she started and purred like a kitten.

    I had the scanner on it.

    coolant temp never raised over 194
    All the heated o2 sensors said ready
    The cam retard was 1deg
    Closed loop was achieved

    and that’s the code it has stored but at the moment not illuminating the check engine light.

    I am going to break down the wiring harness to the ignition control module tomorrow when I have some daylight and see if I find anything lose broken or corroded there

    D017475E-B637-4498-A086-6A30746D4C0F.jpeg
     
  8. Schurkey

    Schurkey I'm Awesome

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    Wouldn't it make more sense to FOLLOW THE SERVICE MANUAL PROCEDURE for tracking down the problem that's causing that code to set?
     

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