Q: Engine shakes when I turn on the car for the first time in the day

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My Pontiac G8 engine shakes every time I turn it on for the first time in the morning but after that the engine doesn't shake any more. I changed the spark plugs but the engine light came on it had come up a few weeks back but I cleared the code disconnecting the battery. Now the check engine light came up again? And the engine still shakes when I turn it on?

My car has 89000 miles.
My car has an automatic transmission.

Hi, thanks for writing in. I’d be happy to provide my insight.

Most likely the fuel pressure is dropping off as it sits overnight. This is a fairly common problem. I’m wondering what the code that was being set was. I would think it would was a random misfire code with this condition though. When the fuel pressure drops as it sits, your motor will take extra time to build fuel pressure. You can test this theory by cycling the key several times before you attempt to start it. Each time you cycle the key, leave it in the run position for at least five seconds, then turn it off. The fuel pump will only run for a few seconds if the motor is not started. Many GM vehicles won’t turn the fuel pump on for as much as a minute after the first key cycle. If you turn the key on an listen for a pump noise coming from the fuel tank, you can confirm it the pump is turning on.

If this makes your car start better in the morning, the next thing to do is locate the source of the internal fuel pressure leak. It will either be in the fuel tank, a fuel injector or the fuel pressure regulator. Although, if it is the regulator, the car will always run very rich, most likely spewing black smoke out the tail pipe.

This is by far the most likely cause for your problem. Anything else will require an experienced technician to diagnose your car as it will not be an obvious problem requiring the use of sophisticated equipment and extensive knowledge of all the car systems. For this reason I recommend the following inspection to help you figure this out: Car is hard to start inspection

If your car does have a loss of fuel pressure, it will take some diagnosis to determine where the pressure loss is occurring. This is usually a creative process that will be specific to your car. I hope this helps and best of luck!

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