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P0316 & P0303

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Jack Hays
New User

Sep 7, 2018, 5:00 PM

Post #1 of 7 (847 views)
P0316 & P0303 Sign In

2003 Ford F1504.2l V6140k miles
OBD Code P0316 & P0303
I understand those codes are telling me my engine is misfiring & that the issue is specific to Cylinder 3. The issue started about three weeks ago - the engine became sluggish, intermittent lack of power, CEL, etc.. I checked my spark plugs (all plugs & wires were replaced at 100k miles) as soon as I got home & all looked just as they should except the one in cylinder 3 - it had obvious dry fouling. So I cleaned that plug up a little & swapped it out with the plug in cylinder 4, erased the codes & then rescanned. Everything was fine at that point. I drove it for a week with out any problems other than it seemed like the gas was kind of bad (I had wondered if I had gotten some bad gas since this started right after refueling) so I added some SeaFoam to the fuel (16 oz to ~7 gal of fuel). After doing that the truck ran like it never had before! No problems whatsoever. I cranked it up yesterday (5 days after adding the SeaFoam) & it was obvious that the P0316 issue was back. I drove it for 3 or 4 miles & it steadily got worse; I barely made it back home. Hooked up the OBD scanner to it & got the same codes as before - P0316 & P0303. I checked the #3 cylinder spark plug & it had slightly wet fouling this time. Would the fuel additive cause the fouling to be slightly wet as opposed to dry? I cleaned up that plug & swapped it with the one from #2 cylinder, erased the codes & rescanned; no more codes & engine ran fine.
Obviously, I have an issue. In researching the codes a number of possible issues were presented - bad fuel, bad plug/wire/coil/fuel injector, vacuum leak, etc. I'm wondering if any of you mechanics out there have an idea what the issue could be based on the limited info I've provided or could kind of narrow things down for me. With there being a number of possibilities combined with me being a non-mechanic who doesn't have a money tree I can't really afford to just throw money at it. I'm due for a fuel filter change so will do that in the next few days.

Any opinions, insight or feed back would be greatly appreciated!

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 7, 2018, 8:02 PM

Post #2 of 7 (839 views)
Re: P0316 & P0303 Sign In

The coil should have been changed at the first sign of a misfire. Simply moving plugs around doesn't do anything but confirm the problem is isolated to #3.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

Jack Hays
New User

Sep 7, 2018, 10:30 PM

Post #3 of 7 (828 views)
Re: P0316 & P0303 Sign In

Thanks for the reply, Hammer Time! Its appreciated. I'll pick up an ignition coil asap & install it.

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 8, 2018, 1:19 AM

Post #4 of 7 (821 views)
Re: P0316 & P0303 Sign In

Jack - Just noted how much SeaFoam you used! OMG - watch out for that stuff that was WAY too much IMO is wildly strong too much will be the problem if it wasn't a problem.
Do the coil but duly noted how fast the problem got worse with SeaFoam use so you said - not surprised. Also do this when you change out fuel filter is have a cleaned, clear glass jar pour what fuel is in a filter from inlet side in and look at it for problems. True bad fuel isn't that common but always a maybe and find it isn't going to pick on one cylinder like this if so,


Jack Hays
New User

Sep 8, 2018, 6:11 PM

Post #5 of 7 (808 views)
Re: P0316 & P0303 Sign In

Thanks for weighing in, Tom! Yeah – I figured I was a bit excessive in the use of the SeaFoam but if it was bad gas I wanted it to be neutralized. I’ll be sure & examine the gas when I change my fuel filter as you suggested.


Ultimate Carjunky / Moderator
Discretesignals profile image

Sep 9, 2018, 7:53 AM

Post #6 of 7 (790 views)
Re: P0316 & P0303 Sign In

Bad gas won't cause a single cylinder misfire. If you decide to replace the coil pack, it would be a good idea to replace the plug wires also even though they were replaced 40k ago. Use a good quality wire set and be sure to route them as the factory had.

Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Sep 9, 2018, 7:56 AM)

Jack Hays
New User

Sep 10, 2018, 10:47 PM

Post #7 of 7 (760 views)
Re: P0316 & P0303 Sign In

"Bad gas won't cause a single cylinder misfire"
Yeah, thats what was throwing me off. The truck acted like it had bad gas and research said that was a possible cause of the P0316 code. One thing I didn't mention in my original post was that initially the only code was the P0316 code. The P0303 appeared a couple of days later in conjunction with the P0316.
I picked up & installed the coil. No codes in the scan afterwards. It took 2 or 3 weeks for the problem to resurface last time so I'll monitor & update the thread as warranted.
The cost of the coil put me over my budget for this past paycheck so I'll have to postpone changing the fuel filter & spark plug wires.
Thanks again to each of you experts for the advise given & knowledge shared. It's greatly appreciated!

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