Missfires when engine wet - Ranger-Forums - The Ultimate Ford Ranger Resource


4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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  #1  
Old 05-18-2017
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Missfires when engine wet

I first noticed this when I was pressure washing my Truck , when I pulled out the engine started to misfire on cylinder 3 . I popped the hood open but couldn't see any excess water anywhere , was thinking that the water was sucked in through the radiator . not sure if it is coil or plug wire problem?
which is the more likely culprit .
If I need to replace either not sure where the best place( in Aldergrove BC Canada Area) to buy at a decent price. also I read somewhere that there are two different coil packs for the 4.0 2004 ranger if so I am not sure which one I have.
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Old 4 Weeks Ago
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Welcome to the forum

Shouldn't be different coil packs on the 4.0l SOHC
3.0l Vulcan engine use two different connectors over the years but same coil pack

Is the misfire gone after a day or so of drying out?
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Old 4 Weeks Ago
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after a few say I drive for a little bit then stop restart engine seems to go away. also occasionally happens on rainy wet days it will start up running rough but same thing I drive it shut truck down start it back up seems to go away. this confuses me . I am ol;d school not used to any engines that run with Computers lol
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Old 4 Weeks Ago
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Not a computer issue

Most likely a wiring issue, well a wiring connector issue
High humidity can cause corroded connection to drop enough of the connection to cause a problem, but works OK in drier weather.
For single cylinder misfire you have the fuel injector and spark plug, so wiring for those would be where to start

2004 should have 104 wire computer connector in engine bay upper center of firewall.
It is in a place where water can get in via the hood gasket.
Unhook battery and pull off the connector, look for any corrosion on the plugs and pins
Each fuel injector has its own wire from computer to the injector, so 6 wires, and these wires Ground the injectors to open them, a slight change in Ground potential would cause injector to not open for the full time, so a misfire from too little fuel

Also check fuel injector connection for #3

Ford uses a Waste spark system which means #3 and #4 share the same coil in the coil pack, both spark plugs spark at the same time, when #3 and #4 are at TDC, so one spark is "wasted", hence the name
Same for #1 and #5, and #2 and #6
There are only 3 coils in the coil pack

Point being if it was a coil issue you would most likely get misfire on 3 and 4 both.
But it can happen, pretty easy to test a coil or coil pack with an ohm meter
Google: test ford coil pack

Yes could be spark plug or spark plug wire on #3
You could swap wires around, and see if problem moves to another cylinder
I think #3 spark plug is pretty hard to get to on the 4.0l SOHC so I would just replace it vs. swapping it.

On the 3.0l Vulcan there is a large Engine wiring connector, not sure if it is the same for the 4.0l SOHC
Wires from the computer, for injectors and coil pack, go thru this connector, so it should also be checked

Last edited by RonD; 4 Weeks Ago at 10:06 AM.
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Old 4 Weeks Ago
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"2004 should have 104 wire computer connector in engine bay upper center of firewall."
I am not sure what your talking about here are you talking about the wiring harness connecting to the computer?


last night I fired up the engine and squirted water all over the coil and spark plug wires , I didn't see any sparks but mind you the engine wasn't under any real load ( if that matters because I only noticed thew miss fire when the engine was under load)
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Old 4 Weeks Ago
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Yes, PCM(computer) is "in the cab" and connector is in the engine bay.
One bolt holds it in place
Video of location here: www.youtube.com/watch?v=-9C3zPpwlfY

Yes, idling engine and engine under load are different, main reason is that a random misfire at idle is usually not "felt", under load you for sure "feel" the loss of power when a cylinder misfires.

No matter what "they" add to the outside of a gasoline engine, on the inside nothing changes.
Each cylinder needs these 3 things to fire
Spark, at the right time
Fuel, with the correct mix with air
Compression, above 100psi

Compression doesn't tend to be intermittent, it can be low which would cause steady miss at low RPMs, that would go away at higher RPMs.

So that leaves spark and fuel
A single cylinder can misfire on a Waste Spark setup but usually not a coil issue

A fuel injector is fairly reliable but with your description, high humidity, I would suspect it.s Pulse signal more than the injector itself

Spraying water on the engine doesn't increase humidity, pressure washing with hood closed would increase humidity in the engine bay, especially if it was warm outside or if engine was warm.
And of course raining weather is high humidity
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Old 4 Weeks Ago
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that makes total sense, I was just outside and the connector is at the center of firewall.
I need to pull the connector off and check for corrosion, if I find a little corrosion and am able to clean it off will this solve the problem? also if so how do I keep water\ moisture from casuing the same problem again ?
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You can usually see a discoloration from corrosion, yes you can scrap connectors and pins just be careful.
To prevent moisture intrusion on electrical connectors you use dielectric grease.
This grease won't conduct electricity.
And because it won't conduct electricity you DO NOT want it to get on the metal contacts and pins, or they won't conduct electricity, lol.

You put it on the edges of the connectors to seal them when they are pushed together.
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Old 4 Weeks Ago
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thanks people. I am going to check the fuel injector wire ,
I did forget to mention on my scan reader it came up with A couple of codes the first is P0457 hoping it is a gas cap problem the other is a p0303, then only once ( quite a while back) it came up with p0316.
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Misfire codes can be many things, P0316 = Random misfires and could be from some "bad gas", has a higher water content than "normal", all gas has water in it, not suppose to but does, lol.
In a gas stations large underground tanks the water will settle to the bottom, but if you are filling up while gas delivery truck is delivering gas to that tank or has just delivered gas to that tank then the water can be stirred up and you end up pumping in more water than "normal"

Then when you park the truck overnight that water settles to the bottom of YOUR tank
At start up the fuel pump sucks in that water and you will get random misfires until water is cleared from fuel lines

P0303 or other specific misfire codes would not be from "bad gas"

Last edited by RonD; 4 Weeks Ago at 11:04 AM.
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Old 4 Weeks Ago
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hmm so I checked all the fires appear to be ok. I am now debating on buy all new plugs wires and coil pack , and I am not really looking forward to doing the plugs closest to the firewall.
any suggestions on where to buy at a descend price I will not do Nappa or Lordco they are way over priced Someonne suggested buying the coil pack through Amazon.ca
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Call local Ford Dealers and ask if they are having any sales on spark plugs and wires, yes I know a Ford Dealer????

I have gotten OEM Motorcraft parts from a Dealer on sale for same price or less than cheap 3rd party parts

Coil packs are usually not on sale but never really looked, my 1994 4.0l coil pack is still running fine
I did change spark plug wires after 17 years, should have done it at 16 years, lol, did cure idle misfires
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Old 4 Weeks Ago
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SO did the wires and plugs Number 3 cylinder took a while to replace plug but I got it. the funny thing is the 1-3 plugs were loose, no more miss fires when engine is wet.
one thing that I noticed also was that when I pulled the number 4 plug I could smell almost a blow by smell or fuel smell.

anyway all is good . next thing is to figure out the the P0457 .
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Old 4 Weeks Ago
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Never would have guessed loose spark plugs

Thanks for the update

P0457 = EVAP system leak

This means when EVAP system uses engine vacuum to put slight negative pressure in the gas tank the pressure is not holding.

Most notice when they stop to get gas there is a "whoooshing" noise when they open the gas cap, that's from the negative pressure the EVAP applied to the gas tank, this prevents gasoline fumes from polluting the air during driving and just sitting.

This is why you will often see "check gas cap" if you google this code
Obviously a loose gas cap wouldn't allow pressure to hold steady in the tank

Most common cause is the Filler and/or Vent tube leaking, these rubber tubes from side of bed to tank crack when they get older and leak so pressure can't be held in the gas tank.

Remove gas cap
Use a hose and rag/towel
Put one end of hose in the filler tube
wrap rag around it to seal opening
BLOW into the hose
Listen for any air leaks, might need a friend to listen under truck and also in the engine bay, vacuum hoses can crack as well.

DO NOT use an air compressor for this, your lungs can generate about 2psi of pressure, more pressure than that WILL BLOW OFF hose connector.
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Old 3 Weeks Ago
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when I bought the truck 2 years ago I noticed that one of the bolts were missing on the truck bed and I can actually slightly lift the upper corner of the bed where the gas filler is. SO if anywhere I am thinking that this is were the problem is. I am going to do the hose and cloth trick unfortunately I don't have anyone close by to help me out but I do have good ears.
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If towel is damp you can usually get a pretty good seal and can tell if tank is leak pressure, not holding it, but code P0457 says that's the problem.
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