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Hello, possible TPS issue?

Discussion in 'GM Powertrain' started by Sierra2500, Nov 14, 2010.

  1. Sierra2500

    Sierra2500 New Member

    Greetings I am a forum newb with a minor issue I am hoping to get advice on. I failed CA emissions yesterday due to higi HC @ 2650 rpm, at idle HC was higher than average but passed. Last week I had an issue with the truck (93 Sierra 2500 5.7) falling on its face off idle when driving, and loping off idle in nuetral. Since there are no trouble codes, I went ahead and replaced the TPS with intentions of doing the TPS and then the MAP. Soon as I replaced the TPS my truck idled 200rpm higher than it had been and the stumble vanished!
    I was pretty stoked since I just kicked Murphy and his law book in the privates =) So, a week later I am on my way to smog and she starts the same symptoms, but I figure hey they test idle and 2500 so shouldnt be an issue.. WRONG! when I got the truck and failed test back she was running just as bad as the previous week before the new TPS.
    So, my question is are the Duralast TPS realy THAT bad, or do I have a possible wiring issue that the fresh TPS simply worked with for a time?
    Right now every sensor except the MAP is under a year old.
    Thanks in advance for any ideas!
     
  2. stephan

    stephan Rockstar 4 Years 5000 Posts

    Welcome to the GM truck club. I'm not sure about the TPS, but high hydrocarbons (unburned fuel) usually indicates the unburned fuel is due to an electrical prob such as plug wires or plugs. It could also be due to a FI problem but if it was, it should be throwing codes.
     
  3. Sierra2500

    Sierra2500 New Member

    Thanks Stephan, I am begining to lean towards the ignition myself at this point. I traded out the TPS with a Delco TPS today with no change in performance, I then replaced the MAP sensor with no change also. The plugs wires cap and rotor have all been recently replaced but in looking at the plugs today I see that they are Motocraft, ewww. Is it possible a poor chassis ground could be the cause here? I noticed also my oil pressure gauge is bouncing at even throttle.
     
  4. stephan

    stephan Rockstar 4 Years 5000 Posts

    LOL I can't believe you admitted you put Ford plugs in your Chevy ha ha ha... Actually there are a lot of posters on here that say Chevys don't like any plugs other than ACs' so the plugs might be worth a try even though they are new. A poor chassis ground can cause all kinds of problems with dash guages & electrical, so before spending any money on other stuff you should definitely check ALL chassis grounds, battery cables (both ends of both cables) engine to body grounds etc. If no ground problems are found it could have a bad oil pressure sender causing the guage bounce.

    If you do end up pulling the plugs, look at them closely & don't mix then up. Mark their numbers & when they are all together look for 1 or 2 that don't match the others in color or contaminates. These will be the cylinders that are most likely causeing your high hydrocarbons, & if the plugs don't cure it then replace the wires for those particular cylinders.
     
  5. Sierra2500

    Sierra2500 New Member

    So I made a home made ALDL cable and hooked up the laptop to the ECM. Long story short my EGR valve was toast, snapping full open at low RPM and thusly causing high manifold pressure and a rich condition. What a pain in the butt to chase down, had a blast with the cable build and software tuning though! One new O2 sensor to be on the safe side and the old girl is a beast once again.
     

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