Pro Advise?

Discussion in 'Chevy C/K Truck Forum' started by redreatta, Feb 24, 2012.

  1. redreatta

    redreatta New Member


    Well, i have been looking for a great forum to ask these questions and it looks like the best are here.

    I have a 386,921 mile 1994 silverado extended cab 1/2 ton with the great 5.7L
    about two months ago the problems started, code 43 popped up and reads {electronic spark control}
    i have read alot of great stuff about this but the problems don't seam like they are the same as what i have. let me explain,
    starts up fine first time every time,runs and sounds great untill it gets warm. after warm up {roughly 7-10 mins on the road}
    it starts to rev up and down while i am driving. not alot just maybe 200-400 rpm. just enough to notice but not extreme. when i get to a stop light it dumps and idles roughly, does not stall just sounds like it is about to. when i jump back on the gas i have to give it a little more than i would like to. if not it sounds like crap. when it is hot and i am driving normal, it idles rough at low speeds but when i get on it, it runs as good as a 400.000 mile original engine will. i have read alot of different stuff but would love to get a opinion from the pros on this site.

  2. tbplus10

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

    That kind of sounds like a vacuum leak, I dont remember if a vacuum leak will cause the spark control to get an error code though.
  3. redreatta

    redreatta New Member

    Thanks for the reply, i have looked the engine over a number of times and am unable to find anything,went as far as a spray bottle with water on every vac line and some brake clean on them also, normally if there is a leak the engine would rev up with the brake clean. or at least it did a couple years ago. i read alot about testing the knock sensor.....gonna try today
  4. Scott_Anderson

    Scott_Anderson Rockstar 100 Posts

    Just a theoretical question here....Is there a crankshaft position/rotation sensor that the ingnition uses for timing? could this prox switch be starting to act up when it's getting hot?
    It definately sounds heat related, just trying to think of what electronics are under the hood or mounted on the engine that control ign and would be affected by heat.
  5. redreatta

    redreatta New Member

    thanks for the reply, no crank sensor on this vehicle. off the top of my head there are knock ,map,coolant,tps,oxygen sensors. i keep reading about the tps and knock are the ones i should look at. i vaguley remember something about closed loop and open loop on something when it is hot,but am still looking. would like to get as much info about this before i go out to look at it.
  6. dipstick

    dipstick Member 2 Years 100 Posts

    You do have a old school crank sensor on the distributor shaft Can ohm it ..see if it is good.
    Take wires loose from ignition module that goes to pickup coil/old school crank sensor watches compression stroke.
    Set meter to ohm,s touch i think green and yellow wire one to a probe other to probe .should read 700 to 1200 ohm,s of resistance.
    Does yours have the electronic spark control beside map sensor? If not i think they integrated it in the ignition control module in 94
    Maybe the problem way to check ign. module due to heat variables.. Oh if you have a bad sensor maybe in limp mode/ limp home till fixed.
    On newer obd11 systems if ecu/ecm/pcm/ computer goes in limp mode will not shift out of second gear ...and cel will flash.
    Could go on but enough said for now.
    Last edited: Feb 26, 2012
  7. redreatta

    redreatta New Member

    Thanks for the reply.

    gonna pick up a esc module this week, got a funny feeling about it and pulled the conector apart earlier, looks like a connection is wasted on it [corroded.] i will update when i install it.was thinking about changing the knock sensor also. any other ideas?
  8. silverhobey

    silverhobey Rockstar 3 Years 500 Posts

    welcome to the site if you are a first time user......if not, WOW...I love the mileage that
    you have gotten out of a GM..............keep er' goin..sorry I don't have any technical
    background to give you any advice on the problem at hand..........Brian from Canada
  9. redreatta

    redreatta New Member

    thanks, got this truck 10 years ago for 2500$ from my father in law{great guy}. it had 116,000 miles on it. I own a small landscape business and it has been great to me, other than normal maint. never had a major problem with it. hopefull for 500,000 before i put a new engine in it,but if i can get more out of it i will.would post some pics but they are above the limit for the site.
  10. redreatta

    redreatta New Member

    heres a pic

    found a nice pic of her

    Attached Files:

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