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Stumble on cold start

RotyP

RotyP

New member
My 2007 lately has been doing something funky. When you go to start it for the first drive of the day on the first time it will fire but it spits, sputters, and stumbles, and then it dies. This takes seconds for it to do, like literally less than 5 seconds. On the 2nd turn of the key it fire up without hesitation. It will not do this later in the day after it has been sitting. Just the very first drive of the day. I cleaned the TB several months ago and it appears to be clean still. Plugs are good and wires are new and it did this with the old wires as well. Anything else that I could try cleaning? Anyone have any ideas why it does this? Its almost like i dont hold the key long in the start position but I dont remember having this problem in nov. when I bought the car.
 


Mine's a 2002 and does the same thing, but only when it's 15 or colder. If I just keep cranking, even when it sputters, it starts fine. Otherwise, the second time it starts fine. I'm not sure what the cause is. I had my car dyno tuned this spring, so I'll see if the re-flash helped with that this winter. What temp is yours doing it at, or does that matter?
 
OP-what heat range plugs are you using? could be fouling a little til they warm up. My car does the same but that's mainly cuz i'm on E-85. But with the scanner hooked up i can feel it smooth out as coolant temps rise. Let it heat up til the temp needle hits the first bar before you put it in gear and drive it, that should help a little
 


Stock heat range plugs because the car is not modified. Synthetic oil? How will this help?
 
Update: it was in the low forty yesterday and the car stumbled started and then died and then started back up fine. Never did it anymore in the day. This morning it was cooler and it stumbled and spat the whole time cranking and then died during cranking process. Second time turning key it fired up instantly. Any ideas?
 


I hope my first post today made sense. I was using my phone and the keypad is iffy. I spoke to a trustworthy mechanic who thinks it is a fuel related issue. Wants me to turn the key on to prime the lines without starting half a dozen times tomorrow to see if it starts easier. I do not have a fuel pressure gauge or I would test the pressure on the rail. He informed me that a faulty coolant temp sensor would normally trip the engine light. I really really hope that the pump on my 2007 is not going out. I find it hard to believe its pump because the car runs fine all day long and in extreme stop and go traffic. Possibly a bad regulator but I'm not sure where it is on this car because I've not dug into that much or taken the time too look.
 
Turns out that "priming" the lines with the key in on position 7 or 8 times made a difference starting the car. It started almost instantly with just a bit of stumble right before. My friend has a fuel pressure gauge that I'm gonna put on it. What readings am I looking for to tell if the pump is bad? Could it be the sending unit? I'm sure they are one piece though. Thanks
 
RotyP said:
What readings am I looking for
Click to expand...
GM Service Manual:
Important: Verify there is adequate fuel in the fuel tank before proceeding with this diagnostic.

  1. Turn OFF the ignition.
  2. Turn OFF all of the accessories.
    Caution:     Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gage. Place the towel in an approved container when the connection of the fuel pressure gage is complete.
  3. Install the Fuel Pressure Gauge.
  4. Turn ON the ignition, with the engine OFF.
    Important:
    • The fuel pump may need to be commanded to ON a few times in order to obtain the highest possible fuel pressure.​
    • Do not start the engine.​
  5. Command the fuel pump ON, with a scan tool.
  6. Observe the fuel pressure gauge with the fuel pump commanded ON.It should be 384-425 kPa (56-62 psi)

    Important: The fuel pressure may vary slightly when the fuel pump stops running. After the fuel pump stops running, the fuel pressure should stabilize and remain constant.
    Monitor the fuel pressure gauge for 1 minute.
    Does the fuel pressure decrease more than 34 kPa (5 psi)?
  7. Relieve the fuel pressure to 69 kPa (10 psi).
  8. Monitor the fuel pressure gauge for 1 minute.
Does the fuel decrease more than 14 kPa (2 psi)?
 
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Can this be done with a scan tool that autozone uses because I do not want to buy one nor do i have the extra money
 
Just hook up the gauge and turn the key on pressure should jump up to above 40, if it starts dropping off you have a bad pump, have you cleaned your tb yet?
 


Fuel pressure with key in on position started at around 50 and never feel below 44psi after key was turned off. Steady pressure at 52psi idle in park. Revved car a bit to 2500 in park and it did not go up but I'm not sure if that means anything at all. Don't think I have a fuel related issue after seeing this.
 
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