Car will not start after short trips, especially in cold weather

KARENPONTIAC

MEMBER
2007 PONTIAC G6
AUTOMATIC
1,000 MILES

My car will start fine in the morning after sitting outside overnight in -20c (-4F) weather. But, if I make a stop somewhere (for coffee/to run into a store, etc.) It won't start again. Similarly, it will start fine after being parked outside all day at work (unplugged, 8 hours) in -20c weather, but if I stop on my way home to pick up some groceries, it won't start again.

If I let it sit for a while (20 minutes) after the first attempt, it will start.
Today (after having made a stop and it not re-starting) I didn't wait the usual 20 minutes, but maybe 1 minute and tried again. It started, but I had to floor the gas pedal for approximately 30 seconds. Which is probably really bad for the vehicle. (Or is this an okay/good "solution?

This seems to be an issue once the temp dips below -15c (5F).

I recently had a new battery installed, but it has not helped the problem.

When attempting to re-start the car, I make sure the radio and heater are turned off.

Could it be the alternator not charging the battery properly?
I do tend to take short trips around town and I typically am only in areas with a 30 mph speed limit. But if that's the issue, why would the 20 minutes wait period in cold weather do the trick?

Overheating fuel pump sensor? (But then why is this not an issue in warmer weather?) Fuel pump issue in general?
Faulty fuses? Something secretly draining the battery? (But again, it does start after sitting for hours)

Thank you so much for any insight!

3 Replies

KASEKENNY

MECHANIC
18,907 POSTS

I want you to do a test drive for me and return to your house so that if this doesn't work, you are not strained somewhere. However, I want you to get it so it doesn't start again and then hold the accelerator down to the floor again. If this works then you more than likely have leaking injectors or some other fuel issue causing too much fuel to get into the cylinders.

What you are doing when you press the accelerator to the floor during cranking is called "Clear Flood Mode." What this means is when the pedal is on the floor during cranking the PCM cuts the injector pulses so that it doesn't add more fuel. If the vehicle starts during this then that means there was already fuel in the cylinders. The fact that it starts after 20 minutes just means that is how much time it takes for the excess fuel to evaporate from the cylinders.

Under normal starting mode, the PCM reads the ambient air temp and determines how much fuel to use. When it is cold it uses a little more fuel to get the engine running hotter as quickly as possible. The fact that it won't restart in cold temp shows that there is not only the additional fuel from the PCM due to the cold temp but the leaking injectors have flooded the engine.

If performing a clear flood starts the engine this is absolutely an acceptable way to get the engine started as that is what it is designed for. In fact, it is better for it then just letting it crank with all that fuel because it is going to foul the plugs.

I would suggest monitoring fuel pressure when you shut it off and I suspect you will see it bleed off once you shut it down. It will bleed down normally but I would think it would take a while. Leaking injectors will cause it to drop pretty quickly.

I attached the info about this and the fuel pressure spec to see if it is low.

Let me know if you have questions. Thanks

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

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