So I have a 01 4.0 that has been giving me some problems. First off it was misfiring on cylinder 3. Changed spark plugs, distributor, and wires and it fixed that. Then was leaking coolant out of the thermostat housing and that caused another misfire somehow so I fixed that but now the misfire has moved to cylinder #4 and I’m getting a lean bank 2 code. I’m stumped to what this could be. Any help is appreciated thanks

 

Welcome to the forum

Misfires cause Lean codes
O2 sensors can only see "air"(oxygen), when a cylinder misfires then no air was burned up with the gasoline like when a cylinder fires, so that air is dumped into the exhaust manifold and O2 sensor sees that as Lean condition(too much oxygen) on that bank
Bank 1 is passenger side, Bank 2 is drivers side, #4 is on drivers side front

So lean code is not the cause, but the effect of the misfire

Cylinders 3 and 4 share the same coil in the coil pack
There are only 3 coils in the coil pack , each coil sparks 2 spark plugs at the same time, this is called a Waste spark system
Coil pack wiring looks like this
[3 4]
[2 6]
[1 5]
Those are the 3 coils
3/4 are paired, as are 2/6 and 1/5

Trace spark plug wires to their cylinders just to make sure they are wired correctly, the 5 6 4 side often gets mixed up

Swap 3 and 4 wires on the coil pack, see if misfire moves to #3
Any pair can be swapped around as both fire at the same time
4 3
2 6
5 1
Works exactly the same as
3 4
2 6
1 5

Run a can of Seafoam or similar injector cleaner in the gas tank, it cleans injector tips

Do you FEEL the misfire under load?
Or is it a light misfire and intermittent

 

 

 

Actually 3 and 4 fire at the same time, each time they are at TDC but only one spark is "used" the other is Wasted, hence the name "waste spark ignition"
Same for 2 and 6, and 1 and 5
Its how the engine is balanced, those are the "match pairs" of cylinders/pistons that are at TDC at the same time, every 120deg of crank rotation
So the video is correct for firing order but not for whats actually happening in the coil

Least amount of time wasting would be to do a compression test, compression is mechanical and either good or bad, so if you take that off the table then you can focus on spark or fuel
But IF it is a compression issue then you won't waste time on non-fixes like spark and fuel

Cold engine, all spark plugs removed, have a good look at #4 spark plug
Test each cylinder and write down results
4.0l SOHC should be 165+psi

If there are any lower psi cylinders put in a teaspoon of oil and retest, psi will go up, but if it doesn't exceed highest of the other cylinders then its a valve that's leaking
You can also Google: dollar bill test
Its an old time way to see if there is a burnt exhaust valve, by no means a definitive test, lol, but it does work
A burnt exhaust valve will allow air from exhaust to be sucked in from exhaust system on the intake stroke of that cylinder, so will pull the dollar bill closer to tail pipe instead of pushing it away, a fuel or spark misfire won't PULL the bill closer


If you have, or can get, an old time timing light you can test if #4 wire is getting a steady spark pulse
"New", coil, wires and spark plugs does NOT mean they are "good", it only means they were NEVER tested, you are the FIRST to use them, so never assume "new" means "it works", maybe 40 years ago it did, but not any more.

A Noid light can be used to test fuel injector pulse
You can also disable spark and crank engine over a few times
Then pull out spark plugs 4 and 5 and compare the tips, both should be equality WET with fuel

 

Relatively easy thing is to Clean+OhmCheck the CoilPack.