99 Yukon intermittently dies an sometimes hard starting

Discussion in 'Engine & Drivetrain' started by Mike Phillips, Aug 9, 2018 at 4:53 PM.

  1. Mike Phillips

    Mike Phillips TYF Newbie

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    At first it would be die for a split second while taking off. This might happen 1 out of 5 times driving. It got a little worse and might do it half the time. Then one day while cruising about 60 MPH it quit for maybe 3 seconds then restarted and ran fine. Then one day it died completely and would not restart. After setting a while it restarted and intermittently died for that split second on the way home. Once or twice when it was cold it acted like it was not going to start but did after leaving the switch on for a few seconds. A mechanic friend of mine said he had a coil go out like that on a customers car so we tried that and it still acts the same.
    Fuel pump was replaced about 2 years ago with a new AC unit. I used to hear the pump run for a moment when you turned the switch on but now it does not.
    Another mechanic says it could the the crank trigger.
    We checked for codes and it give P1860 which is TCC PWM that has t do with converter lock-up but that works fine also.
    Any ideas???
     
  2. drakon543

    drakon543 Full Access Member

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    the tcc also goes through the brake switch if I recall which is an occasional problem in these trucks. worn plug wires could cause this as they would do the same thing as a failing ignition coil. fuel pump relay going bad once it warms up it fails connection and truck dies until the relay cools back down. cold weather could also cause the relay to be sluggish and intermittent. throttle position sensor is also a common issue and sometimes does not throw a code. your at 1/2 throttle and the ecm thinks your not evem touching the pedal to it gets fuel starved and dies or flipped the other way. without actually being there with an advanced scan tool its hard to give your an exact direction to go. there are a number of other common issues but those are almost always tied to a cel trouble code.
     
  3. Mike Phillips

    Mike Phillips TYF Newbie

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    All this has been this summer. The TCC going through the brake switch is interesting in that the cruise control sometimes does not work. As far as the TPS it sometimes does not want to start (no pedal depression) and dies with pedal depression. Who generally has an advanced scan tool?
     
  4. drakon543

    drakon543 Full Access Member

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    the brake switch could definitely be effecting your cruise control. the tps failure could definitely cause your issue. i was instructed once to unplug mine and try to run the truck. i never did it as i found the issue i was hunting(cant remember what my issue was). as it was explained to me if you unplug the tps the truck will try to run a default setting and base the fuel needed off other things. it would probably run rough and or sluggish and have a code. but if it stays running and starts without an issue try replacing the TPS.
     

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