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Old 04-18-2009, 04:25 AM   #1
Lawn Dart
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Lightbulb I fixed my PO300 code!

I just wanted to share this information to anyone that may ever have this problem.

A couple weeks ago, my 2004 Enthusiast with about 61,000 miles displayed an SES light. I hooked up the code reader and discovered a P0300 code; misfire on multiple cylinders. Since it was detecting a misfire, I quickly assumed that something was wrong with the ignition system. Was I ever wrong. First, I changed the spark plugs. $60 later, there was no improvement. Next, I considered changing the coil packs. However, the more I thought about it, not only did it seem expensive, but also unlikely. The probability of every coil pack going bad was pretty slim. There was basically nothing to change after the coil packs, because the only thing left was the wiring to the ECU. Confused, I began to follow the troubleshooting process in the service manual. First thing it recommended was to check for vacuum leaks. I didn't find any, but as the car was sputtering, stalling, and trying to idle in my garage, I noticed that the exhaust tips were collecting a lot of unburnt fuel. This made me want to check and see if the spark plugs were firing properly. I pulled each one out again and they all looked somewhat good, except number four. It was black, a sign of too much fuel. I guessed that the respective fuel injector was not fuctioning properly, and when I checked with my stethoscope, it sounded somewhat different. I just couldn't understand why the rest of the cylinders were detecting a misfire. When I took the intake manifold apart to get to the fuel rail, I noticed that the inside of the plenum was soaked with fuel. When i looked down the intake ports, I could see the most wetness in number four runner, so it was obvious that the injector wasn't closing properly. I guess when the valves were closed, the extra fuel was being sucked up and into the plenum and down the other ports, causing them to be too rich and detect a misfire too. In addition to the new injector, I bought all new intake gaskets, and fuel seals. With a slight discount, the cost was about $172. Finally, she's purring like a kitten again.
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Old 04-18-2009, 04:42 AM   #2
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great info........congrats on getting her purring again....

-J
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Old 04-18-2009, 10:56 AM   #3
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wow great troubleshooting...good to hear shes up and running
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Old 04-25-2009, 04:54 PM   #4
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Something like that is happening to me right now. My car stalled 9 times on route 10 today. I got the same codes but my car stalls with in the 5seconds you turn it on. Thanks for the post going to try it everything out tomorrow when i got some light.
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Old 04-30-2009, 12:33 PM   #5
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Darn i just got the same code, i was hoping it was only going to be spark plugs but now im going to check everything else. Man if its an injector im turbo charged so that might be a litte more pricey......


Question: Anyone have any experience with "snake oil" fuel injector cleaner any brand solutions actually working and solving a stuck fuel injector problem???

Last edited by Chomorro; 04-30-2009 at 12:43 PM.
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Old 05-01-2009, 03:46 PM   #6
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thx for the info
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Old 05-19-2009, 06:58 AM   #7
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Thanks for the info
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Old 10-28-2009, 06:30 AM   #8
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thanks, those problems sound the same as mine. now i have to figure out how can i get the car to a shop and have that looked at sometime today or tomorrow.
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Old 10-28-2009, 08:12 AM   #9
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thanks for the info, having the same problems and I thought it might be an injector. I will have to check all the plugs, the cel light kept blinking twice, so I thought maybe that was telling what cylinder was the problem.
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Old 06-04-2012, 04:54 AM   #10
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I need to get a multimeter and check my coils. I had the code come up 3 weeks after going FI. Thought it was the upstream o2 sensors that weren't on tight. They were replaced and the code still came back. I'm at 114k
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Old 02-22-2013, 11:55 AM   #11
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new motor and still same code. havent gotten to check the injectors, they are DeatschWerks 600cc fuel injectors. im at 14.4 a/f ratio at idle
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Old 03-09-2013, 08:02 AM   #12
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I have a similar problem but mine is intermittent and usually starts after about 30 minutes of driving. Sometimes it will last a while and other times it will correct after a minute or so, making me think it's electronic. I guess an injector can also fail intermittently but I wouldn't think it would be consistent that it would only start after about 30 mins of driving. Anyone have any thoughts? I'm going to look at plugs and coil packs today for any visual indications.
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Old 03-09-2013, 08:52 AM   #13
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If you have a problem with your car you should start with step one that the OP listed.



"Confused, I began to follow the troubleshooting process in the service manual."


First download the FSM and start from there. You will need a multimeter and check resistance on all the parts listed before you spend $$$$ replacing perfectly good parts.
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Old 06-02-2013, 05:20 PM   #14
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So my Z does the same thing. Poor starting, stalls out after RPMs drop, and excess fuel in the mufflers. Still injector issues with no code thrown?
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Old 06-02-2013, 05:20 PM
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Tags
10, 2003, 300, 350z, 370z, code, codes, coil, firing, fix, intake, manifold, nissan, po, po300, troubleshooting



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