I have a 2008 GMC Sierra 1500 Z71 4X4 with a starting issue. Can anyone help?

sgtmggjr55sgtmggjr55 Member Posts: 3
edited October 2014 in GMC
About two years ago I was out hunting and on the last night I was there the temp dropped down to about 6 degrees. The next morning my truck would not start. When I turned the key it just cranked over. it took about four or five attempts but it finally started. Ever since then I have had the same problem every time I go to start it. It always starts, but it takes two and sometimes three key turns to start. Sometimes it only takes one time but about 95% of the time it takes two turns to start. The local dealer said that it was the fuel pump the first time I took it there and then two months later they said it was the Throttle Position Sensor. Then a few months ago a local oil change place ran a test on it when I was having the oil changed and they said it was most likely the Mapping Sensor gone bad, not allowing enough air or something like that. Does anyone have any clues as to what it might actually be? Please help if you can. Thanks.

Answers

  • imidazol97imidazol97 Crossroads of America I70 & I75 Member Posts: 26,440
    edited October 2014
    First thought would be to try turning the key to ON withOUT Cranking for two seconds to run the pump. Then OFF, and then back to ON for 2 seconds to run the pump. Repeat one more time. THEN turn to crank and see if it starts more quickly. That would indicate the system losing pressure since you are priming the system by running the pump before cranking.

    Second would be that a temperature sensor for the coolant has failed and is giving the wrong temperature to the computer. This means the injectors are not putting enough gasoline in for a cold start.

    Third is that it might be the MAF--mass air flow sensor. I am not an expert but with some of those disconnecting the snap on connector before cranking and then seeing if it makes a difference in how the car starts _might_ indicate something.

    If it were the throttle position sensor, you might notice some odd reactions other times from the computer getting the wrong indication about the position of the accelerator pedal. You didn't mention anything like that.

    2014 Malibu 2LT, 2015 Cruze 2LT,

  • steverstever Guest Posts: 52,454
    Interesting - they way I've done the "priming" is to just turn the key to ON for ~5 seconds without cranking. Often you can hear the fuel pump run when you do that. You're looking for the same thing though - a loss of fuel pressure. But I've only used my method to check for a car that sat overnight. After the first crank it would start fine all day.
  • imidazol97imidazol97 Crossroads of America I70 & I75 Member Posts: 26,440
    edited October 2014
    I'd left out the "without" cranking. So I edited to correct that.

    Usually the loss of prime is overnight like you say, and the car starts well for a few hours after having been driven. There might be something more here in the loss of pressure.

    As I've been thinking about this person's problem while doing other things, I realize it also could be the fuel pressure regulator on the line at the engine. It could be leaking the pressure from the fuel line into the vacuum line that leads directly to the engine. I recently read someone with a 3800 engine that had strange starting problems and that was what he replaced that fixed it.

    But I'd expect that to give a start first and then stall, which I believe was his symptom for the other car I mentioned.

    2014 Malibu 2LT, 2015 Cruze 2LT,

  • steverstever Guest Posts: 52,454

    I'd left out the "without" cranking. So I edited to correct that.

    Ah, I did wonder about the cranking.
  • sgtmggjr55sgtmggjr55 Member Posts: 3
    Thanks guys for the information it does give me a place to start with. FYI, I have no other issues with this vehicle. Like I said the truck always starts it just takes a time or two. Once it starts it runs just fine just like the day I bought it new in 2008. Also, it does not matter if the truck has sat overnight or if I just turn it off ten minutes ago,it always takes a couple of key turns to start the engine.

    I know this is an odd problem but any info I can get would be appreciated. Temperatures where I live are very moderate to extreme heat, 50's to 70's in winter and summer is always around 115, so I do not believe cold weather is the issue.
  • imidazol97imidazol97 Crossroads of America I70 & I75 Member Posts: 26,440
    Thanks for the extra information. Do the priming before finally cranking to see if that makes a difference. It may help isolate your problem to the fuel pump leaking pressure back or something in the fuel system being the problem.

    But you mention that you're in a warm climate... Find someone with an upscale reader for the codes. The more upscale ones can read data from the computer. You may even be able to get a loaner scanner from one of the box stores. I have one that tells me the temperature of the coolant that the sensor is reading. When the truck is cold, see if that coolant temp is nearly ambient temperature with it being closer the longer the truck has sat. If the computer thinks the truck engine is warmer than it really is, then the amount of fuel it injects won't be enough for that quick start.

    Try starting with MAF unplugged at its clip.

    You don't mention anything to indicate there might be a problem in the spark part of the engine.

    2014 Malibu 2LT, 2015 Cruze 2LT,

  • imidazol97imidazol97 Crossroads of America I70 & I75 Member Posts: 26,440
    edited October 2014
    If the priming doesn't work and you're a good do-it-yourselfer, I'd find the local box store that loans a fuel pressure tester (O'Reilly/Checkers had one in this area). Connect it with truck cold and see what the fuel pressure is with engine off and then after engine starts. Also pull off the vacuum line to the fuel pressure regulator and the pressure should jump to supply more fuel during acceleration.

    I think this may fit your situation with the check valve in the fuel pump might be your problem. But diagnosis is key to being fairly sure before replacing a part.
    http://www.silveradosierra.com/vortec-5-3l-v8/fuel-pump-or-pressure-regulator-t4441.html

    2014 Malibu 2LT, 2015 Cruze 2LT,

  • sgtmggjr55sgtmggjr55 Member Posts: 3
    Ok guys thanks for all of the info.. After trying the priming the fuel pump theory for the last week it continued to do the same thing every single time. So the priming made no difference at all. Of course the truck still started every time on the second time of cranking the engine.

    Any other ideas fellas? I leave in the next week to go hunting again and have a long drive to get there. I don;t want issues on the road if I can help it.
  • gmcustsvcgmcustsvc Member Posts: 4,252
    Hello sgtmggjr55,

    I see you're requesting assistance from the members of the forum to resolve this concern yourself. If you decide to bring it in to the dealership before your trip, feel free to reach out to us via private message. This message should include your VIN, contact information and current mileage. I look forward to your update with regard to your progress with this concern.

    Marlea W.
    GM Customer Care


  • imidazol97imidazol97 Crossroads of America I70 & I75 Member Posts: 26,440

    Ok guys thanks for all of the info.. After trying the priming the fuel pump theory for the last week it continued to do the same thing every single time. So the priming made no difference at all. Of course the truck still started every time on the second time of cranking the engine.

    Any other ideas fellas? I leave in the next week to go hunting again and have a long drive to get there. I don;t want issues on the road if I can help it.

    I recently saw a starting problem on a GM 3800 car where the own said cleaning the IAC valve getting rid of carbon made a difference. That's a fairly easy item to remove and clean the end as well as the opeing into the throttle body with an intake system cleaner spray and small brush.

    2014 Malibu 2LT, 2015 Cruze 2LT,

  • pgsrpgsr Bakersfield caMember Posts: 4
    I have the same problem  it's not the mass air flow sens I cleaned mine out and it still dose it 

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