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Still hard to start; '96 Z71 engine/computer problems

Discussion in 'The Garage' started by divorced, Mar 2, 2005.

  1. divorced

    divorced 3/4 ton status

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    I asked before about Michelle's '96 Z71 (5.7 engine). It is hard to start after it has sat for a while, usually over 8 hours. It will just crank and crank and doesn't even attemp to start. It takes about 2 minutes to start it. Even after the engine is warm it doesn't start very well, sometimes having to crank 3 or 4 times for it to fire. The check engine light came on and it was a P1406 code, which the dealer said was EGR. He put a new AC Delco EGR valve on it ($150 :yikes: ) and 14.8 miles later the check engine light came on again. It was suggested in my other post that I may have a vacuum leak. The engine has a plastic intake manifold. Twice it has happened that the throttle body stuck closed and it ran very rough; by depressing the gas pedal real hard it would free itself and run ok at higher rpm, but then ran bad again at idle. Could a vacuum leak in this area cause a hard start condition and cause a P1406 EGR code? The dealer is still trying to fix it, but I trust the opinion of my fellow ck5'ers more, and I would like to be educated on this so he doesn't feed me a line of BS. Thanks!

    I'm almost to the point that I would like to return the vehicle and get back our Explorer, but it's already been sold. Since we bought the truck: wipers quit working (I got this fixed at GMC under recall), the heater/AC circuit board went out, the starter quit working, and it's been to the shop for the hard start/engine light problem 4 times, going back for a fifth today!
     
  2. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Prehaps the oil pressure switch is on the fritz? Or maybe the fuel pump is weak?
    Does the pump run for a couple seconds when you put the key to the ON position before you try and crank it?
     
  3. divorced

    divorced 3/4 ton status

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    Yep, the fuel pump runs when I first turn the key, and then I can hear it click off. They tested it and said the pressure was ok. The truck runs great after it finally starts, but to me it seems to idle a bit low - 690 to 700 RPM. I just got back from the dealer and while I was there he tested the old EGR valve with his computer and it was definitley sticking. He then took the new EGR valve off and tested it and it would move in and out when it shouldn't be moving. He said maybe a bad ground or a problem with the MAP? sensor, which is also in the EGR circuit. I left it there again and I will wait to see what he comes up with. :confused:
     
  4. bigyellowjimmy

    bigyellowjimmy 1/2 ton status

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    Its possible that the fuel pressure is bleeding off after sitting for a long time. Is there a schrader (sp??) valve on the fuel rail anywhere that you can check to see if you have pressure before you start it? Make sure you let it sit overnight before checking it.

    As far as the throttle body sticking...have you cleaned it out with throttle body cleaner? (dont use carb cleaner) Its common for them to become gummed up.

    Good luck :thumb:
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    If the pressure tests ok and the fuel pump runs, then bleeding pressure can't be the problem. That will prove the injectors aren't leaking as well.

    Whats the coolant temp sensor telling the ECM the temp is.

    bah, screw that. If the GM dealer is doing their job, they should be looking at the troubleshooting flow chart for a crank no run or hard to start condition, and following that chart to the letter. Nowhere in those charts is the first thing to do "replace parts" like the EGR.
     
  6. Fierospeeder

    Fierospeeder Banned

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    i have to go get something to eat so i wont give a lot of feedback.


    Disconnect the vacuum line to the EGR valve. And see if that helps. Sometimes the vacuum solenoid that controls the EGR valve is bad. Which would turn on the EGR valve under the wrong conditions.
     
  7. divorced

    divorced 3/4 ton status

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    There is no vacuum for the EGR, it has an electronic solenoid to operate it. The old one was definitely sticking though, I watched him test it.


    Dorian - I wish it was at a GM dealer. Unfortunately it's a used car lot. I will question him on what the coolant temp sensor (and any other sensors) are reading. I had asked him if they would cause a hard start condition, he says "possibly" :confused:
     
  8. Fierospeeder

    Fierospeeder Banned

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    It prob is the 3 solenoid piece that goes on top. Those are very expensive.


    clogged converter
    clogged airfilter
    EGR solenoid bad
    Crank sensor bad
    Clogged injectors
    bad ign module

    You need a scope for the module and crank
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    You might try talking with your local GM service department. Mine was actually cool about letting me use a tool (they didn't have it, but they would have let me) so I wonder if you asked nicely, if they'd let you peruse the service manual yourself, perhaps make photocopies of the pages that are relevant.
     

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