What cause the engine to misfire when first start up after it been sit for a while?

Question edited for a lot more clarity.
Question moved to model category.

What did you use to check the code, a simple scan tool, the dash display? A professional grade scan tool computer will tell you exactly which component is causing the number 4 misfire.

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Hello,
Your question lists codes p305p, and p305, which are not valid codes. Did you mean P0305? This is a diagnostic code referring to a misfire on cylinder #5. It looks like you've replaced parts that could be causing a misfire, but did not fix the problem.

A simple check to verify your misfire is not being caused by an ignition coil (the 4.8 liter engine has a coil-near-plug system, with one coil for each spark plug) is to swap the suspect coil (cylinder #5) with a coil from a different cylinder on your engine.

Cylinder #5 is the third one back from the front of the engine on the driver side of the engine. After you swap coils between a good cylinder and #5 cylinder, clear the codes and see if the misfire followed the coil- if a misfire code sets on the cylinder you moved the cylinder #5 coil to, you know the coil has a problem. That will at least help you rule out the remainder of the ignition system.

Coils and wires most likely got wet .

try to change the rotor and the distributor cap and the high tension wire.

You must replace it, that is a heck of a job and not for a person with no auto repair sjills.

Hi Yvonne, I'm glad to help!

The first step when you have a misfire is to see what is causing the misfire. Technicians always rules out mechanical failures before moving on too Electrical issues. What you need to do is check compression on cylinder 2 and see if its good. Remove the spark plug and test it with a compression tester. It should read somewhere around 150 PSI or more. Check it to cylinder 4 and make sure the reading are close they must be within 25 %. If the compression is GOOD then you'll need to move to the electrical checks. Here's how you rule out parts. It doesn't matter if you have plug wires or coil-on-plug. SWAP the parts from cylinder 2 to cylinder 4 and start the engine and if the misfire moves from 2 to 4 then you know its either the spark plug the spark plug wire or the coil pack if you have a coil instead of a plug wire. If the misfire does not move and stays in cylinder 2 then it could be an INJECTOR, WIRING ISSUES, COMPUTER DRIVER. As you see Yvonne it can be a lot of things that can cause a misfire. Hope this helps and have an awesome day Yvonne.

For engine misfiring problem check the help links mentioned below. Click the link below to go through the troubleshooting procedure :---- Engine misses and truck jumps? Hard to down shift? Issue with high gear only? http://technoanswers.blogspot.in/2012/02/engine-miss-and-truck-jumps-hard-to.html

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Bad miss at idle?

http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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Engine Misfire codes for car?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html
Engine Misfire codes?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html

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Misfire on cylinder 4?

http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html

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Oil on spark plugs and car misfires?

http://technoanswers.blogspot.in/2012/02/oil-on-spark-plugs-and-car-misfires.html

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This will help.

Thanks.

Do an injector balance test and a cylinder leakage test. Lets make sure its not fuel related. Most important lets make sure you don't have a vacuum leak.

You didn't post your engine size so please pick the applicable diagram:



1996-98 4.3L Engines Firing Order: 1-6-5-4-3-2Distributor Rotation: Clockwise



1996-98 5.0L, 5.7L and 7.4L Engines Firing Order: 1-8-4-3-6-5-7-2Distributor Rotation: Clockwise




4.3L Engines Firing order: 1-6-5-4-3-2 Distributor rotation: Clockwise



4.8L, 5.3L and 6.0L Engines Firing order: 1-8-7-2-6-5-4-3 Distributorless ignition system (one coil on each cylinder)



5.0L, 5.7L and 7.4L Engines Firing order: 1-8-4-3-6-5-7-2 Distributor rotation: Clockwise

2002 Chevrolet K Tahoe 4WD 4.8 liter V-8 VIN "V"




2002 Chevrolet K Tahoe 4WD 5.3 liter V-8 VIN "T"



Hope helped with this; remember rated this help. Good luck.