P0300 and flashing check engine light

20

Asked by Feb 18, 2017 at 08:34 PM about the 2005 Chevrolet Colorado Z71 Extended Cab RWD

Question type: Maintenance & Repair

Hi my colorado check engine light is flashing and
showing the P0300 code. I've changed my plugs
tested my coils cleaned my map and maf sensor.
Replaced my crankshaft sensor and air filter and
cleaned my throttle body.  And it is idling a lil rough
and lights are still the same. And i checked for
vacuum leaks.I need help! It is the 5cyl 3500

8 Answers

78,975

Possible causes; Faulty spark plug (s), Faulty ignition coil (s), Clogged or faulty fuel injector (s), Intake air leak, Fuel injectors harness is open or shorted, Fuel Injectors circuit poor electrical connection, Ignition coils harness is open or shorted, Ignition coils circuit poor electrical connection, Insufficient cylinders compression, Incorrect fuel pressure...The P0300 code means that a cylinder(s) is misfiring or is randomly misfiring. Start by checking for intake leaks, intake gaskets are common caused of multi-cylinder misfiring. If no leak are found the next step is to replace the spark plugs. If the problem persist more tests needs to be done to diagnose problem.

2 of 2 people found this helpful.
75,365

These engines tend to crack the plastic intake manifold. The P0300 random/multi-cylinder misfire code is what's causing the check engine light to flash. It's warning you that the engine is misfiring and damaging the catalytic converter. With it idling hook up a vacuum gauge to any convenient vacuum port. It should read 21 inches of vacuum at sea level. If not, something is leaking. You can spray starting fluid around the intake manifold and see if the engine smooths out. Use the starting fluid sparingly!! Don't want a fire!! Spray it around the base of the throttle body and around the edges. If something is leaking, you'll be able to find it. HTH. -Jim

1 of 1 people found this helpful.
20

Ok I had a diagnostic done on it today.The #1 cylinder has a slight miss and the #4 has a bad miss. Do compression checks on both and their good. Replaced the coils and checked for air leaks and nothing. And it's still missfiring. Any ideas

1 of 1 people found this helpful.
78,975

Read my possible causes.

2 of 2 people found this helpful.
20

My mechanic told me to ohm out the coil wires. But I would think that there's a small chance of that since cylinder 1 and 4 are missfiring correct?

78,975

Well, you have checked pretty much the major things that cause a miss, and are not coming up with anything. In testing spark plug wires you do this with a digital multi meter set on the ohms Ω setting. Have a lead on each end, the resistance is 8000Ω per foot indicating a good wire. Also have you gone threw and snugged up the intake manifold bolts, check the throttle body screws and base bolts, just go threw an make sure there snug. No over tightening.

1 of 1 people found this helpful.
20

Ok the mechanic told me I have 2 bad injectors. Do you have any how to videos or any information on how to replace the injectors. And do I have to remove the resonator box to get access to these. And would it be a bad idea to buy a refurbished injector instead of a new one. Because there's a pretty big price difference. Thanks for all your help

1 of 1 people found this helpful.
78,975

I have no preference on using a refurbished injector or not, and there is all kinds of video on you tube on how to change a fuel injector.

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