Just changed the plugs and coils on my 05 4x4 with the 5.4L. I used Denso COPs and Motorcraft plugs and I have about 125K miles on the motor. The old COPs and plugs were original.

The issue I am having is a rough idle with the engine RPM between 600-750. The engine also threw a P0174 code, Bank 2 running lean. After a little research, I checked for vacuum leaks and there were none and I also cleaned the MAF with cleaner for MAFs, still in the same situation. I did disconnect a connector on the driver's side fuel rail that I forgot to reconnect, so disconnected the battery and reconnected and I am still at a rough idle.

I drove it around the block and hit the gas hard and it took a while for the engine to kick in but no real acceleration. I suspect that a cylinder or two might be dead and not throwing a CEL or code too.

I am thinking that the upstream O2 sensors might be bad, they are factory originals as is the rest of the exhaust up to the muffler (SIDO). I will post picture captures from my scanner (I used a bluetooth Actron module) later, to get someone to look at what's going on.

Let me know what you think so far, etc.

 

Was it showing any codes before you changed the COPs and plugs? Since it says that it's running lean, I would suspect that the wire to one of the fuel injectors was knocked loose or was damaged when you changed the COPs.

 

No codes, nothing. I did disconnect a couple of injectors so I wouldn't damage the wiring.

 

Here are the screenshots from my scanner, maybe someone can make heads or tails of them.

 

Well, you have 3/4 tank of fuel, and just cleared DTCs (0 miles since cleared, 0 completed OBDII Trips since clear & 0 Miles with DTC ON), battery voltage is good at 13.76 volts, and the engine has been -just idling (14% absolute throttle position @ 587 RPM)- only 3 minutes twelve seconds this run cycle. LOL


On a more serious note, information from a scanner seldom smacks you in the face with a specific part & part# needing to be replaced. Instead, often shows lots of normal stuff mixed with some subtle pointers.


Basically your fuel trims are not the best. The engine is in "closed loop" and fuel rail pressure looks fine @ 39.14 PSI. So WHY is Short Term Fuel trim negative & long term fuel trims positive?? A few misfires will throw FTrims out of whack. You just changed plugs and COPS - and this could be residual from prior to that.


I would recommend - do a battery reset and relearn procedure to clear out fuel trim tables, CHECK / VERIFY ALL electrical connectons to COPS & INJECTORS - replacing any connectors with broken plastic locking clips, run a can of Techtron through the remainder of this tank, and then take another look at it.

 

That's where I think the problem lies, I may of broken a wire when disconnecting the COPs and injectors. I went ahead and ordered new O2 sensors because of the age of the current ones, originals, and a new MAF sensor. When I pulled it to clean it, it looked as though one side of the probe was darker than the other.

 

Probably all good moves. I advocate preventative replacement of O2's around 100K just because the PCM is absolutely dependent upon what they are reporting to adjust fuel injector pulse widths in order to achieve proper fuel/air ratio. If they drift, or deteriorate - all bets are off.


After doing these things, if the P0174 returns, monitor live fuel trims with your scanner while using an 'unlit' propane torch and blow propane all around / under the manifold, vacuum lines, Oil filler tube, PCV hose & connections - EVERWHERE. If you hit a leak, your fuel trims will go BERZERK instantly. My '04 had a leaky gasket on Bank1 UNDERNEATH the IM. When I sprayed underneath the IM by the Alternator - BINGO!

 

I wouldn't replace the O2 sensors until you do more trouble shooting and trying to fix the current problem. The problem with shotgunning problems by just throwing parts at it is that a lot of the new parts can be bad or you can mix up the connectors, damage wires, leave vac hoses off, etc and just create added problems and MORE confusion.

 

I am beginning to think that more and more the issue may lie in the age of the components involved based on the O2 readings and the attached picture. Keep in mind that I have a lot of miles on the original plugs, sensors, etc. Parts are already on the way, saved a bundle through Rock Auto.

I've already checked the vacuum lines and will be doing the manifold test tomorrow. It's a sucky part of the year to work on cars, garage or not.

 

What do you mean? It's in the 80s here. :-)

 

Recently changed the COPs and plugs on my 05 5.4L 4x4 and afterwards it started idling rough and low. I also forgot to reconnect the fuel pressure sensor on the fuel rail before I reconnected the battery and fired it up, keep that in mind.

So after changing the upstream O2 sensors and checking the vacuum lines on the back of the intake (they're connected), I pulled all the plugs and COPs to see if there were issues, all of them work fine. I moved to the injectors and checked the injector connections with a noid light, all of them blinked off and on. I ran an ohm check on the injectors and all of them are between 12.8 to 13.3 in resistance, so no joy.

I then did a cylinder balance test. When I pulled the injector connectors or 4, 7, and 8, the engine RPM and vacuum gauge didn't change. Is it possible that they will ohm test good and still be out?

I had the vacuum gauge connected to the vacuum line on the fuel pressure sensor. Out of curiosity, I disconnected the gauge and ran the engine and the rpm's picked up and the engine smoothed out at idle. Might the FPS be bad also?

 

What your trying to do for diagnostics is no good on computer controlled engines.
Looking at vacuum and pulling coils or injectors connectors does not 'prove' anything.
Resistance checks on coils and injectors are of no value.
If a coil or injector fails a code is set so you can't pick out either one with a meter check.
A cylinder misfire code would tell you which cylinder is the issue.
.
Idle is controlled by the electronic throttle body.
There may be a code set involving that function..
Use a Scanner to take a look.
Good luck.

 

NKY05 - I merged the new thread you started on this subject with your original thread. Creating multiple threads on a common topic can lead to confusing responses that waste your time and possibly cost you extra money chasing a fix.

Good luck on getting your truck running right again.

- Jack