Rough idle and "Check Engine Soon" light - FIXED

[encoly]

Not to hijack this thread, but I have been chasing a P0300, with an occasional P0316, all occurring after I changed out the fuel filter. I've changed plugs twice, plug wires, and coil. I'm now at a loss as to what to try next. This is on the 4.0 V-6 2004 flex fuel. The plugs that I put in were the iridium motorcraft. Maybe I should go back to the cheap double platinum plugs.

 

[Bdang777]

I had the same leak Ranger 03 4.0L V6

I had the same leak 2003 Ranger 4.0L V6 Same leak... The same elbow.

 

[encoly]

After doing some routine maintenance on the battery, while letting the computer relearn everything, I put my scan tool on and was looking at the live data. I noticed that the O2 sensors were reading .35 for no 1 and it was oscillating up to about .55 and no 2 was at a constant .85v. Could this be my major problem? My STFT was moving from plus to minus as it should at idle.

 

[dannyisaacs]

Yeah so after new plugs.. New coil packs... And reset.... It's still throwing 300 304 and 307 codes and running like crap? 2007 4.6l 3v v8 I don't want to keep throwing money at it. Lol any ideas?

 

[encoly]

304 and 307 are misfires of cylinders 4 & 7. If the coil packs were changed on those cylinders, it's possible that the plug wires are bad. At least that's what I would look at next.

 

[dannyisaacs]

There are no plug wires. They are coil packs for each plug. Or do you mean the wires from the harness that plug into the coil packs?

 

[encoly]

Yes. I'm not that familiar with the later v8's, but yes, each pack has to get a signal of when to fire.

 

[Fat Tony]

I've had better luck replacing the rubber piece (on mustangs) using a silicone elbow. They are a better use for this as they dont deteriorate like rubber... I cant remember if the hose is 1/2" or 5/8" that is needed...

But here is a link to both:
1/2" ID : http://www.hps-siliconehoses.com/hps-13mm-90-degree-elbow-coupler-silicone-hose-blue.html
5/8" ID : http://www.hps-siliconehoses.com/hps-16mm-90-degree-elbow-coupler-silicone-hose-black.html

 

[Pontisteve]

Yeah so after new plugs.. New coil packs... And reset.... It's still throwing 300 304 and 307 codes and running like crap? 2007 4.6l 3v v8 I don't want to keep throwing money at it. Lol any ideas?

Don't toss those original coils just yet. They're probably way better than any parts store coils, and they aren't cheap. The only thing that goes bad in a newer coil pack are generally the plugs themselves or the coil boot and spring. What kills coils are misfires (such as bad plugs or bad boots) that are not resolved, and allowed to continue. This causes the coil to work harder, and die trying to jump a larger gap all the time.

Those 3v engines are a returnless fuel system. You can use the scan tool to see what the fuel pressure is. Should be about 40 PSI most of the time once warm. You can look at fuel pressure error, and it should be close to 0.

The returnless system has no return line. Therefore if any junk gets in the rails, it can't get out except to go thru the injector, which has a filter screen on top of each of them. In some cases if you have major contaminants (like a really junk fuel filter that's never been replaced) get into the fuel rails, it can get trapped in there and have no way out, blocking flow to some injectors. Probably the ones furthest away from the fuel lines. Anyway, if all else fails, pull the rails and clean them out. Also clean out the tops of each injector.

You might also want to smoke test the induction system and intake for vacuum leaks.

 

[rrgone]

My 2002 XLT 4.6 started idling weird yesterday and the SES popped up. Read codes and found P0171 and P0174. I knew right where to look thanks to this great thread. Got the updated Motorcraft hose for it coming from Amazon along with a new PCV. I put a piece of HVAC tape on the split elbow temporarily and the idle immediately returned to normal. Thanks Sybertiger!

 

[Dr_Z]

This is what is great about this site. I had the exact same codes as everyone else, came here and got the solution! Thanks - took about 10 minutes of work and the X is running great again.

 

[Krstlbluu]

I have same problem on 2005

 

[Fix4Dirt]

I have same problem on 2005

did you read the solution? or did that not work for you? if not, could you elaborate on the issue, etc? thanks! and welcome to EF!

 

[Curtisizm]

Omg this guy is my hero right now. I have a 2006 limited edition ford explorer 4.6L v8…. And this stupid hose is my exact issue! And not a single parts store or ford place has been able to help me identify what this damn hose is or a part number to replace it!!! I just went through this exact dance with all the parts stores around and not a single one of them could figure out this part replacement!!! It’s been driving me crazy. So I got on the internet and started looking things up for myself because I am tired of my truck having this problem I start a new job Monday and hav got to get it taken care of asap! I stumbled on this post and thread of comments and you guys are literally exactly what I needed and have been trying to find your answer to on my truck! Freaking thank you so much!!!!