1997 F150 5.4 90K, P0304 misfire, coil pack question
 

Would like to ask advice on 1st tune up 1997 F150 Lariat, 5.4 with approx. 90,000 miles, has very pronounced misfire in Overdrive and has progressively gotten worse to the point that on any incline must turn off OD or it will shake itself terribly.My scanner reports code P0304 which I understand is cylinder # 4 misfire. I plan to replace all 8 plugs with Motorcraft AGSF-22F-SMF6, which btw is the p/n that Ford website chat person gave me per the VIN 1FTEF17L1VNB81100.And the same chat person gave me coil pack p/n 3W7Z-12029-AA which I think is DG-508 and seems to be available online at various prices with mixed reviews concerning authenticity.This is my first attempt at replacing 2 piece plugs on these types of engines and coil packs in general. I have watched several you tube videos and will take it slow.I am open to any suggestions and my main questions:1: What is your opinion of replacing all 8 coil packs or just the one on cylinder 4? I am not a fast worker and in light of all the parts that have to be removed to gain access to the coil packs, in my opinion, it may be worth spending $320 (online price, for example, www.fordpartsgiant.com ) on all 8 coil packs if I could trust they are genuine Motorcraft parts. As a comparison, a Brick and mortar dealer retail is $503 for same Motorcraft p/n coil packs. 2: Any recommendations on how to ensure getting genuine OEM coil packs, other than purchasing from a brick and mortar Ford dealer?3: Does the spark plug p/n AGSF-22F-SMF6 seem correct to you guys? As I mentioned I need all the advice I can get.

Thank you

Johnny Walker

You do not have 2 piece plugs, you are thinking of the 2004 and newer 3 valve engine. You also do not have to buy that exact part number plugs, you can go to just about any parts store and get Motorcraft SP479 plugs, those replace the OEM part number. Do not use antiseize on them and torque them to 28 ft/lb. Gap is .054.

Change the plugs first, your coils may be just fine. At 90k it's not surprising that one or more plugs may be causing the miss. Use a small amount of dielectric grease inside the coil boots when reinstalling.

If you do need coils, Motorcraft, Denso, or Delphi are acceptable, they are OEM quality. I would get the Denso at $23.79 each, they actually make the DG508 for Motorcraft.

https://www.rockauto.com/en/catalog/...tion+coil,7060

Thank you so much for the information. I was just browsing the Motorcraft website and by entering AGSF-22F-SMF6 it cross references to SP459 (22F = SP459)So please allow me to understand more, is SP459 also a one piece plug? If so then you’re saying that I can use SP479 in place of SP459, which I trust you’re advice and am fine with using, especially if it is an upgrade plug.However if AGSF-22F-SMF6 (SP459) is a 2 piece plug, then did the Ford chat person give me the wrong part number per my VIN?Thanks again,Johnny Walker

I just did some more research. SP459 is the correct plug for 1997 5.4, SP479 is the correct plug for 1998 and newer 5.4. The only differences are heat range and tip design, in reality you could use either. SP459 is $5.19 at Autozone and O'Reilly, $4.47 plus shipping at Rock Auto.

NO spark plugs for a 5.4 2 valve engine are 2 piece. The 2 piece plugs are for 2004 - early 2008 5.4 3 valve engines which have a completely different head design.

SP459:

https://contentinfo.autozonepro.com/...P-459/image/3/

3 valve plugs:

https://shop.advanceautoparts.com/wc...6_pri_larg.jpg

Note that the new plugs are fully threaded. The ones you pull may only be partially threaded, don't worry about it, the fully threaded plugs will fit fine.

Just remembered something. #4 is the back plug on the passenger side. You may find oil, water, or coolant in the well - this is a common issue. Before removing the plug, use a mirror to look down in the well, clean it out the best you can before removing the plug. If it is wet down there, it may be advisable to replace that coil. Wouldn't hurt to check the other wells while you are at it.

Cause? Intake manifold, heater hose, drips from the A/C pipe, head gasket, valve cover gasket.

Thank you for the pictures. Now I am beginning to understand the difference in the 2 pieces vs 1 piece Plugs. And thanks for clarifying the part number for 1997 5.4 spark plugs. Good suggestion on the mirror.

Will order one coil pack and 8 plugs. Thanks to your help I can proceed with ordering the parts and now have more of an understanding of why #4 is a common misfire on this engine.