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Old 12-13-2010, 06:38 PM
901fan 901fan is offline
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P0309 Help

Hey guys,

I have searched and actually have fixed a few things in advance of posted this request so thanks.
We have a 99 F250 V10 that for a while ran perfectly.
About a month ago it started bucking under load. It threw a P0300 Code.
So I bought some C.O.P's from ebay and installed all 10. Drove it for about a week and again same thing. This time it threw P0300 and then a couple of days later it threw P0309 again. So I bought a FORD C.O.P and a new Motorcraft plug and swapped them out only on Cylinder 9. Again it drove like a champ for about 150 miles then back to bucking, same thing P0300 then P0309.

Within the last month I have swapped these parts as preventative mantainence.
MAF,TPS,Fuel Filter.

I need to check the fuel pressure but at this point I think it is related to fuel as if the tank is full it is not as likely to act up and the last time it acted up it was right as the tank got low.

What should I check next? I ordered a New fuel Inj for that cylinder.
Any thoughts on quick fixes?I have not checked for vacuum leaks.
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Old 12-14-2010, 06:53 AM
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Krewat Krewat is offline
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If you keep getting a #9 misfire (0309), it could be an injector on cylinder #9 based on what parts you've changed. The injector isn't spraying right, it fouls the plug and it starts to misfire. When you pulled the plug, what did it look like?

You might also want to do a compression check and compare the other cylinders to #9.

Sometimes, from reading here, a single injector seems to be able to cause a random misfire, because it will screw up other cylinders at the same time.
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Old 12-14-2010, 08:01 AM
901fan 901fan is offline
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Thanks for the reply. The plug was black at the base, I will have to grab it again and see exactly what it looks like. I am hoping for it to be the injector. It has not burned oil or done anything odd until now so I am hoping it is not something internal.And the fact that it comes and goes, sometimes if you hammer it it will clear up and run fine for a while. I would think if it had some compression problems it would act up constantly.
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Old 12-14-2010, 05:23 PM
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I read one time about a guy that had a similar problem. His O2 sensor was bad and caused the engine to run rich and foul plugs. I'm not saying change the O2 sensor, just might want to check the Ohms.
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