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Dodgerench, ASE Certified Technician
Category: Chrysler
Satisfied Customers: 3407
Experience:  30+ years Dodge/ Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
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2007 pt cruiser: colder..wont put on diagnostic computers

Customer Question

In cold weather(0 degree or colder) our 2007 pt cruiser wont start. This happens only once every winter. We have had it put on diagnostic computers and no one can find a problem. It turns over well but wont fire up. Could this be a bad sensor or what?
Submitted: 7 years ago.
Category: Chrysler
Expert:  Dodgerench replied 7 years ago.
HiCustomer welcome to Just Answer!.

With no codes being set, I wouldn't think it to be caused by the loss of an important sensor... they'll usually leave a trail behind. My best guess would be that the engine initially flooded, then lost compression due to lifter pump-up.

Extreme cold makes it tough on any engine to start, even the port-injected type like your PT uses. With gasoline slow to evaporate, it takes a fair amount of fuel delivery before a combustible mixture finally develops, but it might come too late if the spark plugs have become wet. I like to give the engine an assist on super-cold mornings by adding a little accelerator pressure, which adds air, not fuel. It's a long-held myth that you'll flood your engine if the throttle is touched when starting (something apparently true on Fords), but the reality is that it actually reduces the likelihood of flooding on our speed-density type fuel systems. Pushing the throttle adds only air at cranking speeds, with the fuel system supplying the proper amount of fuel to match.

Clearing the flood can be as simple as pressing the accelerator completely to the floor to employ the clear-flood feature, a process that shuts injection off during engine cranking. As the engine starts to regain signs of life, you can lift a bit on the accelerator to resume fuel injection as required. It will usually start unless carbon deposits drop off the intake valves from the solvent action of being wet with fuel. That's when loss of compression can happen.

The valvetrain on your 2.4 engine is hydraulically adjusted for zero-lash... no clearance between any valvetrain parts for quiet, maintenance free operation. As soon as clearance opens up from carbon being caught between valve and seat, hydraulic lash adjusters will fill with oil to take up the space, holding the setting long after a piece of carbon debris may have passed on. This results in a situation where the intake valve fails to close completely and the engine loses compression. You may notice a different sound coming from the engine compartment when (and if) that happens... instead of a distinct speeding-slowing of starter speed as each compression stroke is reached, the engine may sound smooth, almost turbine-like.

Unfortunately, the cure for this is continued cranking until the lash adjusters bleed down and compression is restored. Thick engine oil in those temperatures will slow the process somewhat, sometimes taking a few minutes of wide-open throttle engine cranking before things settle back to normal and you begin to hear signs of life again.

Use of wide-open throttle during this process is recommended to prevent the engine from becoming hopelessly flooded. Crank for a while at WOT... lift off the accelerator a bit to restore injection... return to WOT. Eventually, things will sort themselves out and within seconds of it running on its own with one or two cylinders, the engine will rev up and smooth out. Hold engine speeds up for a short while to heat and dry the spark plugs and things should be good from there.

This is something that can happen to pretty much any engine from any make, year or model. Your 2.4 engine isn't more predisposed to this type of no-start problem than any other, but I have seen it happen on occasion. Since it leaves no traces behind once running again, it seems to fit the description of what you're seeing on your PT once or so per year.

If you have any questions, don't hesitate to write back. I'll be glad to help.

Dodgerench and other Chrysler Specialists are ready to help you
Customer: replied 7 years ago.
Dodgewrench: Thanks a lot!! Really! We have had this problem for a couple years now. It only happens once . As soon as it starts up it doesn't do it again until the next winter. You saved us a lot of money. It's a great car otherwise. bbits
Expert:  Dodgerench replied 7 years ago.
Great news, bbits! Thanks for the update. :o)