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Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 36078
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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Shawn. I have a 2004 F150 4.6. It has 129K on it. I am

Customer Question

Hi Shawn. I have a 2004 F150 4.6. It has 129K on it. I am getting recurring codes p0303, p0316, and p0174. I have been getting the 0174 for a while. When it started running rough I replaced the plug and coil on #8. Still getting the misfires. I have checked for vacuum leaks visually, and tightened intake manifold bolts on that side.
Submitted: 2 years ago.
Category: Ford
Expert:  Ron replied 2 years ago.

Hello and thank you for your question,

The code P0303 indicates a engine misfire on the #3 cylinder and the P0316 means the computer is seeing a engine misfire in the first 1,000 revolutions . Has the coil, spark plug and injector been checked on the #3 cylinder?

Customer: replied 2 years ago.
I am sorry, it was a typo, the code is P0308, P0316, P0174
Expert:  Ron replied 2 years ago.

Okay since you are sure the new coil is okay and you have good spark out of it to the new spark plug then I would next run a compression test on the #8 cylinder to be sure its okay and if the compression checks okay then I would swap the #7 injector with the #8 and see if the misfire moves. If you are sure there are no vacuum leaks you could very well have a bad injector and that could also cause the P0174 to set. Check test thing for me and post back and we can work from there.

Customer: replied 2 years ago.
OK, I will try swapping the injectors. One other piece of information. Before it started misfiring, for some several months, I would get a cel every time I added fuel. It was the lean bank 2 code and it would clear after several restarts.
Expert:  Ron replied 2 years ago.

Okay the code P0174 can also set due to the PCM trying to lean the system down, before you swap the injectors make sure to check the compression on that cylinder to be sure its with in specs. One other common cause for this code to set can be caused by a leaking PCV supply line so be sure to check it as well.

Customer: replied 2 years ago.
My research last night was leading me to suspect the PVC line
Expert:  Ron replied 2 years ago.

If its leaking it can cause the cylinder Misfire and #8 is the closest one to the source so yes be sure to check it before you do the other steps.

Customer: replied 2 years ago.
OK. Maybe a day or two, but I will check that out, will not have time for a couple of weeks to do a compression test if needed.
Expert:  Ron replied 2 years ago.

No problem, I'm here if you need me, start first with checking the PCV supply line from the valve to the intake where ti connects, if you find its leaking this will likely resolve the problem and save you from having to to the other steps.

Customer: replied 2 years ago.
Hi Ron. I fixed the truck tonight. It was none of the things I had been looking for, or that we were talking about. I checked the PVC lines tonight and did a vac leak check with carb cleaner and nothing came up. Then I kept thinking about something I had read a couple of days ago about an exhaust leak before the O2 sensors could cause the lean bank 2 code, so I crawled under the truck while it was idling and sure enough, it was leaking at the flange between the exhaust manifold and exhaust pipe. I got my torque wrench and tightened up on the bolts and as it sealed I could immediately hear the difference in idle. Checked the strim/ltrim for bank 2 and the strim was right back where it was supposed to be. Cleared the codes and drove it around the block and the ltrim had come back to normal as well. Problem solved.
Customer: replied 2 years ago.
This is probably a good service, but as you did not get me to the solution, I believe I am entitled to a refund.Thanks
Expert:  Ron replied 2 years ago.

Glad to hear you got it resolved and I am paid nothing unless you rate my service, any money you have paid remains in your account and if you would like a refund you will need to contact customer service.