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#2 Cylinder Mystery Misfire


Rangerdanger408

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Hey everyone, thanks for checking out my post
I have a 1999 v6 3.0L XLT Normal Fuel Automatic Ford Ranger with a #2 Cylinder Misfire. It is the only code that is coupled with a rough idle. The rough idle started right before the code was thrown, with a smooth history of running fine.

I have replaced
Spark plugs & Wires
#2 Fuel Injector
Fuel Filter
Ignition Coil

I have Cleaned and inspected
MAF sensor
EGR Valve

I have Conducted
Compression test - about #160 all around
Block test three times and passed
Vacuum test with starter fluid everywhere with no change
Check for any tubes out of place

The truck starts fine, and then immediately starts running rough at idle, which feels like a constant misfire. As soon as I give it some gas or get above around 2000 RPM the engine runs fine. Highway speeds seem to run well until I get around 50-60 MPH, and the automatic transmission shifts down, and it feels like it starts misfiring again. There is an audible click in the new fuel injector, and I have also pulled the valve cover and everything looks in place. I added fuel and Oil treatment which hasn’t done anything to change how the engine runs. I don’t know where or what to check next, any help would be much appreciated. Thanks for your time
 


RonD

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Welcome to TRS :)

Reads like you have tested the Big 3 reasons for a cylinder to misfire
Spark
Fuel
Compression

Does the misfire only happen on cold start?
Or does it happen at idle, cold or warm?

I assume both since you said misfire reoccurs under higher loads, i.e. higher gear, lower RPMs = high engine load

Your engine uses a Waste Spark system, so spark plugs are fired in PAIRS
The Coil Pack only has 3 coils inside, yet sparks 6 cylinders..............because they are Paired

Coil pack wiring is:
3 4
2 6
1 5
front

or
1 5
2 6
3 4
front

depends on which way the coil is mounted

But those are the Pairs
1 and 5 fire at the same time, as do
2 and 6
3 and 4

This means you can REVERSE these spark plug wires at the coil and engine should run the same
So swap 2 and 6 wires at the coil, see if misfire moves to #6

Because the Pair of spark plugs are wired in Series, that means one spark plug sparks from center to tip(normal) and the other sparks from tip to center(reverse), which is fine.
Just a heads up to never use single platinum or single any "UM" spark plugs in a Waste Spark system, waste of money, 3 spark plugs will wear out the same as regular copper.
So double platinum or regular copper
And this is why you will often find TWO spark plug numbers listed as "stock", 3 had platinum tips and 3 had platinum centers, when buying spark plugs by the 10s of THOUSANDS, a few cents matters ALOT, lol
When buying 6 not so much



One thing idle and higher engine load have in common is high Vacuum in intake manifold.
As #2 only misfires under these conditions, it could indicate a vacuum leak at #2 intake port, and the extra air only at high vacuum is fouling the mix.
Could be on topside of lower intake, where you tested with starting fluid, or the lower side where you can't test.
Not sure a smoke test would help if its the lower side

But as you said, and documented, you have tested everything else, so just guessing.

Yes, Ford injectors can be quite loud, tick, tick, tick :)
 
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Rangerdanger408

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Thanks for the reply RonD,
I forgot to state in the post, but I have swapped #2 & #6 wires with the same result, as well as changed the plug and swapped plugs. I also have unplugged other wires with a noticeable change (due to misfire being unplugged) but when I unplug #2 there is no change. I have also pulled the #2 plug out while connected and tested for spark which it has. I do feel like it is indeed a vacuum leak, and will most likely be taking apart the intake manifold to check gaskets. Is there any other way I can check the intake for a vacuum leak to make sure it is a vacuum leak? I have sprayed the hell out of it with starter fluid with no change
 

Fordblue213

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Did a new plug make it run fine for a little while, then the misfire came back?
 

RonD

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Thanks for the reply RonD,
I forgot to state in the post, but I have swapped #2 & #6 wires with the same result, as well as changed the plug and swapped plugs. I also have unplugged other wires with a noticeable change (due to misfire being unplugged) but when I unplug #2 there is no change. I have also pulled the #2 plug out while connected and tested for spark which it has. I do feel like it is indeed a vacuum leak, and will most likely be taking apart the intake manifold to check gaskets. Is there any other way I can check the intake for a vacuum leak to make sure it is a vacuum leak? I have sprayed the hell out of it with starter fluid with no change
Lower intake vacuum leaks are pretty tough to detect since they only effect 1 or 2 cylinders usually.
If it effects 2 then you can get Lean Codes on that Bank or higher fuel trims on that Bank.
And if leak is on the underside of lower intake then smoke test wouldn't work.

It could be a sticky valve in #2, but because the misfires occur only at high intake vacuum that would be long shot, but not a "no shot"
You can spray penetrating oil into an idling engine which can temporarily stop the sticking and the misfire.
Using a Vacuum gauge while doing this is best, as you can see the misfire by the gauge fluctuating, and then see it stop misfiring(fluctuating) after oil is injected, which is better than "listening" for the misfire :)


Bluetooth OBD2 readers are not expensive, and is a good long term tool to have.
They work with any vehicle sold in the US or Canada since 1996, so not Ford specific or even "made in the US" specific.
You can watch Live Data while driving to see if fuel trims on passenger side bank(Bank 1) is higher than Drivers side(bank 2) on average.
That could indicate vacuum leak that only effects Bank 1.
But the misfire itself can also cause high fuel trim, so not definitive
 

Rangerdanger408

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RonD,
I forgot to answer one of the questions about the idle, which it seems to misfire regardless of engine temperature but seems to get better at a hotter temp. This might just be my mind playing tricks on me though.

Where would I spray the penetrating oil? I do have a vacuum gage I can use for the test

I do have a stock simple code reader as well, which if this helps at all

Under a cold start
ST FTRM1(%) -2.3
LT FTRM1(%) 10.9
ST FTRM2(%) -6.3
LT FTRM2(%) 3.9

After warm the LT FTRM1 still remains pretty high
 

RonD

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Yes, higher + LTFT(long term fuel trim) on bank 1 would point towards smaller vacuum leak on lower intake.

Computer runs cold engine on a Richer mix, Choke mode, as O2 sensors get hot, 650degF, they come online, then computer can use them to Lean out the Rich mix.
And this is when misfires would probably be more noticeable if its caused by vacuum leak.
So that fits, but isn't definitive.


You spray a light oil, like penetrating oil, into the intake while engine idles or any RPM that has the misfire.
This can prevent sticking valves temporarily.
On older cars we would add a light oil to gas tank, lol, to prevent sticking valves on a longer term bases.
I think now a day people use Marvel Mystery Oil(MMO) for that
 
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Rangerdanger408

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RonD,
Thank you for the help, I will be spraying the oil and then most likely taking apart the engine in order to find and hopefully fix the leak. You have been a great help, and I will post results
 

RonD

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You have tried everything else so..............lower intake gasket would be next on my list
 

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