So to start, I had a small misfire between 40-50 mph which I read was a common issue with warn plugs. My factory plugs had 80K and I decided to do it myself since the dealership wanted 6-800. I broke 3 of them but was able to get two out easily and one was pretty tough but got it out with the lisle tool. I put the new design Motorcraft SP-515's in and my truck ran perfect, so I was happy. However after a few days I noticed a smell of gas in the cabin with the vent or heat on, it was winter time. I read that the plugs have to be torqued to 25 ft/lbs which I didn't do when I put them in.

Next I figured since I was going to torque all the plugs, I would go a head and put new COP's in. I went cheap and bought the Chinese ones on Amazon for $45 bucks for 8 of them, and put them in and everything ran fine and no gas smell. So I thought I was good to go.

Next, I notice my exhaust hanger flapping hanging and realize my exhaust has broke off right past the muffler. I take it to my exhaust shop and have it a new one put on from the cat back. I leave the shop and my check engine light comes on. I figure maybe my exhaust has been bad for a while and it just needs to relearn the idle with the exhaust working properly. It seems to run fine by the time I get home after about 10 miles on the highway. I use a code reader just to see the code (misfire #4 cylinder). I delete the code and am good to go.

I drove it for about a month and notice a misfire very rarely to start, not as bad as the original issue before I changed the plugs but I noticed it. Then one day on the way to work it starts to idle real rough and check engine light comes on. I figure since I got that cylinder 4 light before I would just change to one of the old COP's on that cylinder and be good to go. I did that and unhooked the battery to delete the code without checking it (regretting that now). Issues doesn't get better.

Then I figure it was the cheap COP's I put on and I read on the reviews they go bad after two months sometimes. I suck it up and buy Accel's and put them on thinking that would fix it. Same issue, maybe running a little better but still rough at idle and still feels like it has a misfire. So now I am stumped, I have a mechanic who works on my stuff on the side but can't get to it for a week or so. I thinking it maybe a bad plug, but no codes so I don't want to change out all 8 plugs find the bad one. I am also starting to think it might have something to do with the exhaust, since that is when the issues really started, but I am not even sure how that could cause this issue. Any ideas?

I don't post on here, but always check here for my truck stuff and have been a member since 09 when I bought my truck. So thanks for the help.

 

Accel cops don't have a very good record either.

 

It doesn't seem like anything involved in these plug and coil changes have good reputations. I am more leaning towards one of the plugs is bad since I changed two sets of coils with out helping the issue. I hate that its not throwing any codes so I can't narrow it down to one cylinder. I actually went and cycled one of the original working coils and through all of the cylinders before I purchased the Accel Coils and I still couldn't narrow it down to a single coil. I have read reviews on the Motorcraft plugs saying they are bad sometimes, so that could be my issue. I just hate to replace every one or cycle a new one through to find a bad plug if that isn't the issue.

 

I hear you. If your code reader will give you OBDII Misfire Mode $06 diagnostic data, it will give you misfire counts by individual cylinder for both the current drive cycle and the accmulation for the last 10 drive cycles. That should help narrow it down. However - with respect to a bad plug ... rather than a defective plug out of the package, I'm more prone to think a new plug may have been damaged or internally fractured by forcing it into one of those carboned up holes where extraction force was so great it twisted the old plug off, requiring the Lisle tool for extraction.

I've cought some "flack" about this theory, but it has successfully worked for me for many thousands of miles now and you might consider some of the information in this post:
https://www.f150online.com/forums/v8...ml#post5159499


... and there is a lengthly followup later in the same thread.


Hope this might help.

 

Your theory make sense, however in my case you would assume that the issue would have shown up right away and not months down the road. My father in law has a code reader but I think its more a basic one, what price range code reader would pick up the $06 codes from the previous drive cycles?

 

Are you sure it's not a bad injector? the 05s are infamous for leaking injectors. You did say you smelled gas?

 

I smelled gas after the original spark plug change in early March. I torqued them down and that went away and I haven't noticed it since. I am not ruling out the injectors, once I rule out a bad plug I will probably look into the injectors.

I spoke to my mechanic last night and he gave me a few things to try, he thinks it could possibly be a cracked plug from shipping or installation. Which would make sense as I have seen a number of reviews for the Motorcraft SP-515 on amazon saying they got bad or damaged plugs. I really just need to narrow it down to a single plug/cylinder or take all plugs out and inspect them. He mentioned taking it to Advance and getting them to do a diagnostic for free, would that pick up the $06 data, someone had mentioned? I believe he has a scanner that will but can't get to it until next weekend.

 

It is near an absolute necessity to have at least SOME kind of code reader to do your own work on these vehicles now days. It could even provide valuable information toward @Roadie's thought. (ie: Short Term & Long Trim Fuel Trim - O2 Sensor readings and Cat Efficiency readings). Otherwise, Its like playing chess with a damn computer. You just about can't win!


I'm certainly no expert on code readers (or much of anything for that matter), and don't know which of the code readers give OBDII Mode $06 reports. I got started (by happenstance only) using the Torque Pro (App $4.95) on my Android cell phone with a bluetooth adapter (around $15 - $20) on the OBDII port. And it does it magnificantly. I CAN tell you though - whatever facility you use requires some research / digging to make good use of the diagnostics reports. The "$" sign indicates "HEX", and reports / results are coded in HEX. Many are "instantaneous" readings from sensors. As a result, a curious reading at one instant doesn't ALWAYS mean there's a problem. The ECU monitors systems continuously for extended periods before setting a DTC. Prime example - Misfire Counts on a per cyl basis. When the count exceeds a "certain" factory set level, a 30x code is set. Mode $06 just gives you an instantanous snapshot of those counters, (and other stuff). You need a list of the "$"Tests and the "$"Results for your specific model vehicle to make sense of the reports no matter which code reader you end up with.


You can download the Motorcraft Manual on OBDII Theory for your 2005 F150 from here
http://www.fordservicecontent.com/fo...t/OBDSM508.pdf


------- EDIT ------ Specifically, read the MISFIRE MONITOR theory of operation, Pages 8-11. -----

Hope this helps
F150Torqued

 

F150Torqued I will look into reading the specific codes under $06. I can't open the PDF on my work computer. Any idea if the diagnostic scanner they use at Advance will read the $06 data?

 

No Idea. Sorry about the link. (I've double checked it and it works). It's pretty large but I highly recommend that you get it somehow, it has more info about what is going on inside your PCM than you might ever guess.

 

Sorry if I wasn't clear. I can't open it at work because of some issue with direct links to PDF. I can open it on my phone and at home. I just will wait until I get home to look at it on a bigger screen. I can usually do a work around and save it on my phone and email it to work computer as a file. I guess I will take it over to Advance tomorrow or Friday and see what it says and compare to the link if it does.

 

UPDATE: So I found the issue. I am still a little puzzled. So I changed my fuel filter and put some injector cleaner through the my truck last Friday and it still ran like crap. I then took it to AutoZone to get them to scan it and it came up with no codes. I ended up picking up a spark plug while at AutoZone (SP-515). The last thing I could think to do before I took it to my mechanic was to change out the plug on #4 since that is the only code I got back when I got the new exhaust put on even though it seemed to correct itself and run fine for a few weeks after. BOOM my truck is running perfect. It seems strange to me a plug would fade in and out like that but I will take the $13 fix. For as bad of a misfire as I was getting I can't understand why it wouldn't throw a code, I am glad I didn't have to cycle through all the spark plugs.

 

Glad you finally solved the problem and thanks for posting the fix.