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Re: my expedition check light engine on code#po306
You need to see if there are any codes in the OBD system.That's a good staarting point.
Based on your description, and how on '89 6 cylinder Ford I had ran, I would think it was a throttle position sensor. But you need to check for codes, and last resort, find a copy of the Factory Service Manual (not Hanes, not Motors, not Chiltons) at your local library. The FSM's give you all the diagnostic checks that the dealer techs use.
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Faulty EGR valves do not cause "false" misfire codes. An EGR valve that is not closing properly can cause misfires (and misfire codes) but they are REAL misfires when this happens.
To understand this, you need to understand what a misfire is and what kinds of things can cause them. It is a very LONG list and I do not have the time or space to get into all that here.
You will also need to understand this if you are going to properly diagnose your misfire codes without wasting a whole bunch of money on parts that you do not need. MANY things can cause misfires other than spark plugs and ignition coils.
I do not know what EGR code you are getting, but I will tell you that in the 37 years that I have been diagnosing and repairing cars, there has only been once that I can remember that I have ever replaced an EGR valve on a Ford engine because the valve itself was faulty. Most EGR codes on Fords are caused by either clogged-up EGR ports or a bad DPFE sensor. Every so often you will find a bad EGR control solenoid or a broken vacuum line, but it is extremely rare that the EGR valve itself the cause. With the exception of leaking vacuum lines and on certain engines, clogged EGR ports (Like the 6 individual EGR ports in the 4.2L engine), none of these causes for EGR codes will cause any misfires.
Also, most of the time when people pull the trigger on the ignition coils on the 5.4L and 4.6L engines, all the thing really needs is new spark plug boots. They get contaminated with oil and water and can cause carbon-tracking on the spark plugs and/or arcing into the spark plug wells instead of sending the spark through the spark plug. It is pretty much the same thing as having bad spark plug wires on a conventional ignition system. You don't throw the coil and distributor away on a conventional system because it needs new wires. Neither should you replace a coil on a COP ignition system that just needs a boot. Some auto makers do not make the boots available seperate from the coil. Ford at least had the insight to understand that people cannot afford the cost of replacing all of their coils just because the boots are defective.
code po306 means cylinder number 6 misfire detected, possible causes air leak in the intake manifold or in the egr or pcm system, could have mechanical problem number 6 cylinder like burned or worn valves,could have clogged fuel injector or faulty fuel injector,could have bad ignition coil, bad spark plug or bad spark plug wire.
Has it had a tune-up yet? (New spark plugs) If not, you're due. Also, have the shop test your coil packs - a very common problem with the Expeditions. I had my plugs replaced and No. 2 coil pack replaced recently for around $340. I'm a handyman, but would never attempt to change the plugs on mine myself - too much could go wrong- breaking a plug off, special tools, etc. This should fix your problem.
Most likely you have a bad COP (Coil On Plug) .
Maybe more than one. Very common ford problem for last 12 years.
If you get a MIL Light on the dash (the wrench),check for a PO300 Code.
A PO304 would be coil #4,PO306 #6 Etc.
Cyl 1 thru 4 on pass side
Cyl 5 thru 8 on driver side,front to back
Also hills cause a hi engine vacuum and thus a possible EGR Valve going bad. You can unplug the vacuum lines and plug, to diagnose that issue.
Also leave the EGR disconnected if your working on coil issues. Just note the MIL light will stay on all the time,and remember to check your 300 codes if you feel a hesitaton or miss.