I have logged fault codes P0300, P0301, and P0303. What is the problem?

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Misfires are noticeable. I don't feel like I can go over 50mph. These displayed about 20 miles after filling up a nearly empty tank. I can't siphon a gas sample to check for water because a rollover spillage blocking device is in the tank. I replaced plugs and swapped the coils to no effect. I cleaned the MAF to no effect. I can't hear or see an intake problem. I have the Torque Pro app but don't really know what to look for to diagnose this problem. I did notice my STFT2 was over 20% while STFT1 was -5%, but MAF at warm idle is 2.4g/s, load at WTO is 85%. If you could give me pointers on how to check 02 sensors or other possible culprits with the Torque Scanner app, I'd be very grateful!

sparejayden in Washington DC

Nov 14, 2013

3 Replies

Popular Answer

pushrodon Nov 15, 2013

You did swap the known good coils, 2 & 4 with the 1 & 3 coils i assume? Back to the basic tests, compression, vacuum, ignition and fuel. You should find the problem with those tests! If not equipped to complete, get some hands-on help.

sparejaydenon Nov 18, 2013

Thanks to all of you for your help! I ended up getting help from a friend who is a mechanic. He first drained the fuel tank and put in some shell premium. Following that the only code that remained was P0303. So he swapped injectors 1 and 3 and the code moved to 1. He installed a new injector in 1 and everything appeared fixed. Except a day later I was driving along and got 2 cat codes, P0420 and another. I don't happen to recall exactly right now. But I was afraid of something like this because I drove about 100 miles with those misfires!! So now I have some more research to do. I am really hoping this doesn't lead to a new cat before christmas!! Not at all what I asked Santa for.

pushrodon Nov 18, 2013

Have the 02 sensors tested with a scan tool, mechanic can tell from live data if cat is failing. Possible downstream 02 fault.

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globalhelperon Nov 14, 2013

COULD BE ELECTRICAL ISSUE OR INJECTOR

cardocIIIon Nov 15, 2013

You have the information that we need to start testing for the misfire, and the bank to bank fuel trim suggests at the least a potential downstream O2 sensor fuel trim issue, or it could be an airflow problem such as a cam out of time or a restricted exhaust on just one side. The bank taking away fuel would potentially be the side that isn't breathing as good as the other bank. Miss-fires kill catalysts, this needs addressed before it gets worse.