Check out link below...
https://www.obd-codes.com/p0305
You will notice it lists burned exhaust valve as a possible cause and although it also lists poor compression, it is worth adding the intake valve to the list - it doesn't need much of a seating defect before combustion gas will leak past the valve, blowing away the incoming charge and resulting in what behaves like a very lean mixture even though the charge could contain around the correct amount of fuel.
If no other cause is found it should be noted a standard compression test is practically useless and a cylinder leakage test is practically the only sure way to a diagnosis.
SOURCE: firing orde ford 6 cyl f-150 truck distributer to spark plugs
you didn't say if you have the straight 6 or v 6.But i'll give the order for both.
The 4.9L straight 6 is 1-5-3-6-2-4----------- distributor rotor turning clockwise, and #1 plug is the first plug.
On the 3.0 and 4.2 V6 engines is 1-4-2-5-3-6-------#1 plug is the first plug on driver side---- facing engine.
SOURCE: 2002 ford ranger 3.0 is missing on 2 cyl plugs ok injectors ok new coilpack
do a compression test,as the intake manifold,like alot of fords is no good.
SOURCE: Broken spark plug in the head on a 2005 Ford F-150 5.4L
i also work at a dealer, and it is a poor design. carbon biulds up on the extension of plug and you cant get out.Have a broken plug in front of me as i speak. Change plugs at 40 k or you will pay!!!
SOURCE: ford e 150 4.2 Misfire cylinder 6
do a compression test, you may have a bend valve , I'm assuming its not getting overheating so I don't think its the head gasket..a compression test can give you the answer..hope this was very helpful...thanks
SOURCE: my 1984 ford f-150 turns over,but wont start,it
There are a few things you can still check to locate the weak spark issue.
The first is the battery. you should have it tested. If it's showing a low voltage this may or may not be because the battery is bad. You need to consider the age of the battery first. & years is about the life of the average auto battery. If it's newer then that the alternator and or the wires could be the cause.
Inspect the battery cables and alternator wiring.
The cables and terminals should be cleaned and a little Vaseline applied to combat corrosion. All the wiring in the starting circuit should be inspected for loose or damaged connectors and corrosion. Also look for any wear or kinks in the wire covering. A thin spot on a wire can bleed off voltage and interrupt the signal. Get a can of Dielectric grease and spray the inside of all the connectors.
You replace most of the ignition components but how about the ignition control module. Although when the control module goes bad the symptom is usually no spark but it can affect the coil's performance resulting in weak spark also. Before replacing the control module disconnect all the terminals and check and clean any corrosion you find. Apply some Dielectric grease spray and reconnect and check your spark.
More then likely following these steps will take care of the problem.
If after you have checked everything here and the problem persists please respond with all you checked and any results and I'll try and help narrow the trouble down.
Hope this helps.
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