Hey all. My 2006 XLT 3.0l has a very small miss at idle say sitting at a light. Truck runs 100% but, can't figure out the miss. I bought it about 3 months ago with 85k on the clock very clean but wanted to give it a little love maintenance wise to make me feel better. The following is what I have done it since getting it.

New plugs and wires, coil pack ,fuel filter, serpentine belt, oil filter change, cleaned MAF and throttle body, also ran some Marvel Mystery oil through fuel system a few times. The miss was there when I got it and it's still there. Like I said it's hardly noticeable and I can live with it but, just wondering if someone has any ideas. Thanks in advance.

Cheers!

Andrew

 

BTW. I really don't notice it at high idle just low idle @750 rpm

 

You should have a misfire code in memory, no these don't always turn on the CEL(check engine light)

Stop by an auto parts store and they will read the codes for free, WRITE DOWN any codes
Auto parts guys are not mechanics, so grain of salt if they suggest buying something to "fix" a code number

Never "Google" an engine code, look it up on a FULL LIST like this one: https://therangerstation.com/tech_li...II_codes.shtml

Computer has several codes it can choose to use, the codes it does NOT use can tell you more than the code it did use
I.e. if you have a misfire code but no injector code or coil code then could be compression issue
Engine codes are not as straight forward as the english translation/definition would have you believe, lol

 

Hey Ron. I checked for codes and live stream data on my scanner. I have a quality Autophix scanner due to the fact that I also have a Jaguar XK8 (required). No active or pending codes reported. The miss I'm taking about is more of a slight rumble or shudder at low idle. Most folks probably wouldn't notice it but, **** me does. Like I said I can live with it cause the truck runs excellent otherwise. Just wondered if anyone had a similar symptom at low idle. Thanks

 

Maybe its not a misfire

Lets say you have a vibration at 750rpms
Maybe fan clutch?
Power steering pump, try turning the steering wheel at warm idle and see it vibration changes, that puts more stress on fan belt as well which changes load on engine

 

Good thought Ron I will check that out. Funny thing is I don't get the rumble all the time

 

My 2004 auto makes quite a range of strange noises at idle. It runs great and I have not been able to identify much of what I hear. Sometimes I thought it was misfiring mildly, and sometimes I thought it was hunting in rpm, but if I listen at the exhaust or watch the tach it's nice and steady. It's just a little unrefined. I suspect most of it is the auto and the cooling fan. Sometimes at idle in traffic I hear something turn on and off with a fairly loud click - I suspect that's the fan but don't really know.

 

Hey 8ton. maybe it is just unrefined and I have a critical ear for such things? The clicking you are hearing is your compressor cycling on and off. It was making me a little crazy when I first got my truck. I have found that the only setting where the compressor doesn't cycle is in the vent position (switch to the left). I can live with that

 

Wait, what? The A/C compressor? Now I gotta look at the wiring. I knew it turned on with defrost but didn't think it was on otherwise. I actually don't like A/C and hate having that thing sucking up power and wasting fuel. I wish it had a separate button so I could decide when to turn it on.

 

Strange but true.Most vehicles cycle the compressor to remove humidity from the interior ie... defrost mode. For some reason even selecting foot/vent mode (switch to the right) the compressor cycles on and off. Try your setting in the vent mode (left) and you won't hear the clicking. I know.......

 

I'll be damned, I just looked at the diagrams and that's what it shows. The 2008 is even worse and the diagram shows it on for every position. Then again the wiring diagrams for these are so inconsistent and full of errors it's hard to be sure - the 2002 and 2005 diagrams I have don't show the Floor/Vent position at all. They do show Vent as not activating it.

Now I have to decide if I'm going to add a defeat switch or modify the existing HVAC control panel so it only comes on at full defrost or A/C. At least I now have one avenue to improving the mileage.

 

As long as I can get some heat in the vent mode without it cycling I can live with. Is strange though

 

I like to have the heat at the floor to keep my feet warm, and it will run the compressor then. Sorry I've pulled your thread well off topic - if/when I do a mod I will start a thread on it. Gonna get a new control panel at the junkyard before I do anything.

 

Yes, around 2000 and earlier OFF, VENT and FLOOR did NOT cycle AC on, later years added FLOOR to AC activation, OFF and VENT didn't activate AC

 

Just wanted to bump this thread a bit. Did clean the ICV thinking that might help. Nope, same low idle rumble.

 

Try a wider spark plug gap, if its at .045 go to .049, so bump it up about .004

 

The nominal plug gap for my 2004 Ranger is 0.054", according to the sticker under the hood (1.29 - 1.45mm or 0.051 - 0.057"). I see a lot of references to 0.045" as the official gap, but I consider the sticker to be the correct number. It runs well that way anyway.

 

I thought just the 4.0l ran the .054 gap
But yes you can go a full .01 up or down but .005 is biggest change I would do at one time, then another .005 if it works better

 

I can see the logic behind changing the gap but, old plugs (worn) and new plugs made no difference at all. In other words I'm sure the gap was much wider on the plugs I took out (I didn't check the gap on the old plugs). Have to say for 85k the old plugs were slightly worn but, not bad at all.

I know this is a minor problem but, I have to admit this is making me a bit crazy considering everything I have changed and cleaned.

New plugs and wires, coil pack ,fuel filter, oil/filter change, cleaned MAF, throttle body and ICV, also ran some Marvel Mystery oil through fuel system a few times

I'm just out of ideas?

 

Well there are only 3 reasons a cylinder can misfire in a gasoline engine
spark
fuel
compression

If you think you have eliminated spark and fuel then time to test compression

Most shops can do an electronic compression test using a laptop and software, only take a few minutes to set it up but not sure what they would charge
Its done by timing and speed
The crank and cam sensor's signals show rotational speed and the pulses are the timing, if say cylinder #3 firing does not add the same amount of speed to crank than the rest, it would be a partial misfire meaning its compression would be lower
And if it was a compression issue then it would occur at any RPM, you just wouldn't feel it at higher RPMs, so if it goes away at say 2,500rpm then its a spark fuel issue not compression, if its still there are 2,5000rpms then its a compression issue

Compression gives a "rebound effect", like winding up a rubber band stores energy then can release it, the more you wind it up the more energy is stored and then released
So if a cylinder has lower compression it can't add exactly the same amount of "energy" to the crank, some but not exactly the same, so at lower RPMs you may feel that as a vibration, not a misfire, a partial misfire because it doesn't add the same energy to the crank

 

Ron that totally makes sense. I really don't think it's spark or a fuel problem as I believe I have addressed the usual suspects. Compression test might be the next step trying to figure this out. Today I added some Tectron and added some mid grade fuel to see if it made a difference so far no good. As far as the spark fuel issue, I just can't feel or hear anything when driving.

 

The thing about spark plug gaps is from Rich mix the computer has to run a warm idle, its Rich when engine is cold but engine is also at higher RPMs so often can't feel a slight miss

The Rich mix is so engine doesn't overheat at idle, and it can cause partial burn with smaller gaps, so not a full power explosion

Spark plug gaps are set for general use, wider gap is better for lower RPMs, but there is less recovery time for the coils so at RPMs above say 4,000 you may get a misfire or two
Smaller gaps give coils more recovery time so better for higher RPMs, basically racing, lol, but can cause misfires at lower RPMs.

And then there is the timing when spark actually happens which changes with the size of the gap
You want full explosive ignition to happen at about 8-10deg After TDC, this gives the piston and connecting rod the best leverage to push down on the crank to add to its power
Full explosive ignition does NOT happen when spark plug fires, that just ignites the air/fuel mix near the spark plug, that ignition must spread out, which takes "time"
So you will often see 12deg Before TDC as base spark timing at idle, spark plug fires at 12deg BTDC to get Full explosive ignition at 10deg ATDC
As RPMs increase the spark plug may fire at 25deg BTDC, to get Full explosive ignition at 10deg ATDC, because piston is moving faster but air/fuel mix still takes the same amount of time to fully ignite.

So IF....a spark plug has a different gap it may cause Full explosive ignition to occur at 15-20deg ATDC which means its firing OK but not adding full power to crank

 

Hmm -

Poor injector spray pattern, slight leak in an injector, leaking egr valve, pcv valve?

 

Truthfully I am going to throw a PCV valve in for the hell of it.

Ron I appreciate the input on the spark plug gap and your explanation makes total sense. I think at this point I will live with it until I find someone that can do the electronic compression check that you advised. I'm new to this area and have not yet found someone I am confident with who can actually trouble shoot this problem but, I'm not giving up on it.

Again thanks for your guidance and input

 

Just a quick update.

Thought I would check for vacuum leaks at least to eliminate the possibility. Used starting spray with engine running everywhere I could think of. No leaks detected and absolutely no difference with rumble. Just thought I would update thread.