My CEL came on and the code is P0301. Mileage is 125,540 with a manual tranny. I put new plugs in made sure they had the correct gap. Inspected the Motorcraft plugs I had put in about 60,000 mile and they all looked very similar. I did a dry compression test on cylinders 1, 2, & 5. 1 and 2 were 150 and 5 was 152. Tested the fuel injectors 1& 2 and they were in good working order. Cleaned the MAF sensor with MAF spray cleaner. Cleared the code and drove it and the CEL returned (P0301). I know my 12V battery is weak and needs replacing. Could my weak battery possibly cause a CEL and a misfire?

Thanks,
Mark

 

Welcome to the forum

No on the battery, once any engine is started the alternator provides ALL the voltage at 14volts, new battery is at most 12.8volts so voltage flows TO the battery at that time
Battery is only used to start the engine, then is off-line as far as voltage out

Do you feel the misfire?
So its real not a computer/sensor glitch

Were the spark plugs both out when testing 1 and 2
If a head gasket blows between 2 adjacent cylinders both can give false higher compression

Best compression test is with all 6 spark plugs removed this gives higher cranking speed, and the SAME cranking speed for each test
And 5 "hits", at least, for each test

 

Hi Ron,
I did not do the compression test with both plugs out. I can feel the mis at idle and at low speed. I will redo the compression test.

Best regards,
Mark

 

Hi Ron,
My issue was a broke valve spring. No piston damage. Had both heads removed and ended up with a valve job. Truck is back together and is running great. At the same time I replaced the radiator and hoses. Hopefully it will go for many more miles.

Best regards,
Mark