Had my check engine light come on in my 2004 so I checked it out with the scanner and i got a P0305 code. Now I know that it means that a misfire in cylinder 5 was detected, I just want some advice on going about finding out what is causing the misfire before I start buying parts. What should I check first and so forth? I know the 3.0 engines have the infamous issue of the valve seats and Im really hoping I wont have to do any head work and that its something else..

 

Check the spark plug wire from the coil pack to the cylinder and see if you have any spots that have been warn through, and make sure that its not grounding out the spark

 

Determine whether it's a spark, fuel, or air issue.

Most commonly a spark issue, so you'd be best off checking that system first.

 

I checked out the Spark Plug Wires from the coil to the actual spark plug and they seem in good shape. I also checked for grounding of spark and that checked out ok as well. I think my next step will be to do a compression test. First it threw out a P0305 and today I drove it around a little bit and it threw out a P0304? What gives?

 

Multiple cylinder misfires are usually a failing coil pack. Could be sticking injectors, but that is less common. How many miles are on your sparkplugs? You should do a tuneup every 30K miles if regular copper plugs, or every 100K if using Motorcraft Platinum plugs

 

Last time I changed the spark plugs was about 7k ago. Would it be wiser to do a compression test first then go from there? Or get a new coil pack then go from there?

 

If you have a known-good coil pack lying around, you could swap it in as a quick n dirty test. If you don't, I'd test the spark with a visual spark tester, make sure it's working or not.

A compression test would come near the end of the diagnostic funnel, as that would be looking for base mechanical reasons for the misfire.

 

I don't have a extra coil pack laying around so I can't do that...Ill look into getting a visual spark tester. Do they sell em at any auto parts stores?

 

The coil is 3 coils with 2 outputs each. Usually only one side of the coil shorts. I like to take the wire of the missing cylinder and switch it with the wire strait across the coil as they fire together. I watch live missfire data, but you could switch wires, clear codes, then see which missfire code comes back. If the misfire moves to the switched wire cylinder the coil is dirt. If it stays the same missfire code its that plug, wire, injector, or compression. Sounds kind of stupid but it works. Coils fail alot esp. on cars were there in the rear taking alot of heat over a manifold.

 

Alright let me make sure i got this correct, since i got a misfire on cylinder 4 I should take the plug from the spark plug on cylinder four and switch it with the one on the other side of the engine correct?

 

This is a very common way of doing it, but let me try to simplify what i think he means.

Take the wire for plug 4. and switch it with the one next to it. like say 5, or 6. at both the plug and the coil. if the misfire moves to whichever plug that is. buy some new wires.
i think its a wire issues. its rare that injectors ever go bad and stop working. and i doubt a compression test will reveal much.

 

Oh alright I got it thanks for clearing it up DangerRanger.hopefully its the wires or something of that sort and not the heads that I need to replace on this 3.0

 

No dont move the wires on the plugs just the missing cylinder strait across the coil. Two plugs fire at the same time on these coil paks so your just changeing which output on the same coil fires which plug. It takes literally seconds if you are watching live missfire data. If you cant watch data then youll have to wait for a code to set.

 

So I went outside earlier today and did exactly that. Switched the plug straight across on the coil which was cylinder 1 and then ran it a little bit and I got the same code, P0305. I didnt realize it before but I noticed today that it was throwing another code as well P0316. As much as I dont want to admit to it I feel it might be the head issue...

 

I just ran into the same problem. It can also be the camshaft position sensor and camshaft sequencer. I Had my truck throw a p0304 and a p0316 and fixed both of those and now I'm all good. Check this out. http://www.therangerstation.com/tech...on_sensor.html

 

If you buy the sequencer it comes with a new sensor at least mine did and it was only 50 bucks at my local auto supply store.

 

Hmm I didnt think of the CPS. Did you have a rough idle as well? Or what exactly were your trucks symptoms? Also, how hard was it to replace? I might just go out and buy it tomorrow and replace it.

 

Took out Cylinder 5 spark plug to inspect it and it seemed fine. Then I put it back took it for a drive and it drove pretty well. Once I got home I hooked up the scanner and I got a P0300 code?!?!?

 

Anyone know what size fitting or type of thread I need on the fitting that goes into the spark plug hole for a compression test? I tried one that seems to have the same thread pattern as the spark plug but it wouldn't stay in.

 

http://www.aa1car.com/

Try looking at this, maybe it will help. Save this to your favs. for future references. Good luck. More than likely it's just a bad coil pak.It really shouldn't be that hard to diagnose.

 

Thanks a lot for the link. Very informative!