2002 4.0 misfires

[Speedwagon]

Recently bought a 2002 4.0. One of the first things I did was to replace the spark plugs, since I had no idea what condition they were. Did some searching, and got the Autolite XP5144. I had intended to wait and get the Motorcraft plug wires, but the wires that were on there did not want to come off easily, and I broke a few removing them. So I ended up getting what the local store had available, which appears to be the same rather cheap wires that were on the truck before.

Since doing this, I've had random misfires. Feels like mostly at idle. Truck accelerates fine when I give it throttle. No check engine light.

Any guidance on troubleshooting and fixing this?

 

[Dirtman]

What did you gap the plugs at?

 

[Speedwagon]

What did you gap the plugs at?

I didn't, I left them at what they came at. I was under the impression you don't gap iridium plugs?

According to Autolite, the XP5144 comes at 0.054, which is spec for the 4.0

edit:
Per Autolite site, now that you mention that, I found this

Fine Wire Plugs
Plug manufacturers typically warn against gapping fine wire spark plugs due to the fragile nature of their electrodes. However, Autolite understands a spark plug can only operate to its optimum potential if properly gapped. Proper gapping technique should be followed with any spark plug, but special care should be taken with fine wire plugs. Autolite will not warranty a plug who’s center electrode is snapped during gapping.

 

[Dirtman]

You don't gap iridium plugs with a typical wedge style gapping tool because you can damage the electrode or plating. But you should always still check the gap carefully with a feeler gauge and if they need to be adjusted, do so by using a gapping tool that bends the prong from the back and doesn't touch the tip.

 

[Speedwagon]

Gotcha. I'll verify gap on them then, and report back.

Since the engine is still hot, and I don't want to burn myself on the exhaust, going to wait for it to cool down a bit. In the meantime, I hooked up my laptop with FORscan, for a mode 6 test. Got the following:

Misfire rate for cyl 1 & 3, 0.00%
Misfire rate for cyl 2, 4, 6 0.16%
Misfire rate for cyl 5 0.32%

No check engine light, but the following codes are present:
P1000
B1877 (safetybelt driver retractor circuit failure)
P0500 (VSS sensor circuit failure)
C1230 (wheel speed sensor rear center input circuit failure)
P1816 (trans neutral safety switch circuit failure)
None related to misfire, but apparently I have things that are possibly going bad

 

[Speedwagon]

Owner's manual says gap should be 0.054. The sticker in the engine bay has 0.062-0.068

Which one is right?

 

[Dirtman]

I can't comment on what the sticker in the engine bay says but I have never heard of a gap that big. @RonD is the expert here. I think .051-54 is correct. Larger gap means harder spark but less recovery time. So a big gap may miss at high rpms, a small gap the opposite. Itll work good at higher rpm but may miss at low.

 

[sheep herder]

Chilton's manual says .052-.057. For whatever that's worth.

 

[RonD]

For the 4.0l SOHC or OHV its 0.054, emissions sticker is wrong

If you didn't have rough running before changing the plugs and wires then there is a problem with the new plugs and wires, lol, I know duh

So what brand were the old spark plugs?
Never did like "fine wire" spark plugs, kinda like a "fine wire" tow strap, I am sure it has its uses but not for ME

You can crack insulators when installing spark plugs
You can wait until its dark out and look at the idling engine when its dark and see how much the spark plug wires are arcing, that will cause rough idles

Spark plug wires have stand offs, plastic holders, that keep them away from metal parts of the engine to prevent arcing

 

[Speedwagon]

For the 4.0l SOHC or OHV its 0.054, emissions sticker is wrong

If you didn't have rough running before changing the plugs and wires then there is a problem with the new plugs and wires, lol, I know duh

So what brand were the old spark plugs?
Never did like "fine wire" spark plugs, kinda like a "fine wire" tow strap, I am sure it has its uses but not for ME

You can crack insulators when installing spark plugs
You can wait until its dark out and look at the idling engine when its dark and see how much the spark plug wires are arcing, that will cause rough idles

Spark plug wires have stand offs, plastic holders, that keep them away from metal parts of the engine to prevent arcing

Bosch plugs came out, Autolite went in.

And yes, I assume I did something.

I called a dealer about the discrepancy in gap, and they told me the sticker is the correct one(this was before you posted). I just gapped it to that, and the truck does feel a bit better than before. The mode 6 diag in FORscan indicates only 5 & 6 are having an issue now. The plugs all looked lean to me though, not much browning on them. So I'm going to try changing the fuel filter next, and see what that gets me. If that does nothing, I might try the least expensive Motorcraft plugs, and see what happens.

 

[RonD]

There is more than a few posts out there about better running with the wider, 0.065, gap, so why not

2002 Owners manual says 0.054
2002 Emissions Sticker says 0.065

Motorcraft plugs will last longer than any other brand, Autolite is 2nd
Use the larger gap as you see fit, its YOUR truck now not Fords

1989 - 2011 Rangers with coil packs use a Waste Spark system
This was the very first spark system ever used, uses Crank timing not cam timing
Ford sparks TWO spark plugs at the same time in two cylinders, they are wired in Series
So 1 spark plug has "normal" spark, center to tip, the other has "reverse" spark, tip to center

Because of this, single "coating" spark plugs won't be good to use, because 3 of the spark plugs will wear out the same as regular copper/nickle with no coating
So either use 6 regular spark plugs, no coating, or use 6 Double coating, so tip and center both have the coating

 

[Dirtman]

There he is... Listen to ron

 

[Speedwagon]

I was still getting misfires on 5 & 6 according to mode 6 test. So I thought I'd try moving the plug gap in a bit on those 2. It didn't like that at all. Made it noticeably worse. So I picked up a set of motorcraft plugs. Those go in shortly.

 

[Speedwagon]

I don't think this engine likes the 0.054 gap. Motorcraft copper plugs(verified gap at 0.054), with brand new motorcraft wires, still getting misfires. I did find that the aftermarket wires I put on were garbage. 5 & 6 pulled apart this last time, when I went to put the motorcraft plugs in. Which explains the misfires on 5 & 6. Going to try a larger gap today, see if it runs better.

 

[RonD]

And just a heads up

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

The 5 6 4 side gets me quite often, either at the coil or at the cylinders on that bank, 3.0l uses the same setup

These are Matched pairs, 1/5 spark at the same time, as do 2/6 and 3/4, so each pair shares one coil in the coil pack
[3 4]
[2 6]
[1 5]