2001 Mercury Mountaineer Cylinder #1 MisFire Help | Ford Explorer - Ford Ranger Forums - Serious Explorations
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2001 Mercury Mountaineer Cylinder #1 MisFire Help


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March 31, 2022
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2001 Mercury Mountaineer
Hello All,

I've been a lurker on these forums for awhile and always found them helpful, but this issue has been stumping me for awhile and I want to verify with others where I think my next step is. Please read through everything if you have time to understand what I have done and things I've noticed.

Info on the car for your reference: 2001 Mercury Mountaineer, 4.0L V6 SOHC.

I have had a misfire on cylinder 1 for at least a month, here is what I have already replaced: replaced the plug on cylinder 1, replaced the plug wire, and even replaced the ignition coil pack, the issue usually went away for about a 15 minute drive after each change, which might just be coincidence.

Currently, I was able to get my hands on an OBD that can connect to ForScan. I happened to be able to measure some values both with and without a misfire. I want to say it is the injector itself but I can still here is clicking or ticking, even when the misfire is occurring, so I am a little confused. Here are some screenshots of the data with a misfire and without a misfire.

Here is a still frame of the car misfiring:

Here is a still frame of the car NOT misfiring after about 5 minutes to allow for fuel trims to settle:


What I noticed is that INJ1_F is shown as "Yes" during the misfire and "No" when the engine is running fine. However, this only points that this is derived internally to the ECU that the harness, connector, or injector has an electrical fault. Maybe someone can shed some light on the accuracy of this reading.

Additionally, the LTFT during the misfire is pegged at 25%, but after the engine ran without the misfire for about 5 minutes to LTFT is sitting pretty at 2.34%

So from what I gather I know the misfire has to do with something from the ECU to the Injector itself. However, what I find confusing is that the injector still clicks with or without a misfire and I did rig up a noid light that showed when the engine was running the bulb flashed. Could the injector just be clogged, I couldn't see how that would tell the ECU there is an electrical fault though... So I am finding it hard to be 100% sure that the injector is at fault, but strange things happen so I wanted some input here from everyone.


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It’s possible it’s clogged. Not having fuel will cause a misfire. A weak fuel pump can also cause a misfire, but it’s usually distributed amongst the cylinders.

Most of the time a misfire code for a specific cylinder is a problem with the injector

The ignition is waste spark and there is no feedback to the pcm from each cylinder

So the pcm can easily spot a misfire on a specific cylinder when there is an injector issue
It takes far more drive cycles for the pcm to use timing info to try and determine which cylinder is misfiring and it can give its best “guess” based on when the misfire occurs when it is an ignition problem

Just because the injector clicks does not mean it is spraying a clean mist

Have you checked fuel rail pressure?
My bet is your injector is having issues

Many many many times I have fixed a misfire code on the 4.0 v6 by finally removing, cleaning and bench testing all 6 injectors and re sealing the fuel rail and intake plenums
It is fun to watch a semi clogged injector free itself and start spraying again

With the sohc engine the injector sit inside a plastic “hat” and they can deteriorate and cause blockage
It’s worth a quick look in there, it literally can take 15 minutes to remove the sohc upper plenum
Good idea to Re ring the upper and lower plenums, upgrade the thermostat housing and replace the drivers side chain tensioner

Sorry for the late response, had some other things come up recently. I appreciate all the advice! Seems as though it's agreed there is something wrong with the injector itself whether it is a clog or just a faulty injector.

Any recommendations on brand of fuel injector to go with other than Motorcraft? I feel it would be best to replace all 6 injectors, o-rings, and those plastic fittings they sit into at the same time. However, I'd rather not spend $400 on injectors if there is a brand that is trusted that I can get for cheaper because this car isn't getting any younger!

Thanks for the suggestions, I'll check for cracks and blockages before replacing the injector, however, not a lot of time recently.

Bosch injectors
Remanufactured and flow tested
Sets available on ebay by reputable sellers for around $80-120

The injector seats can be had online too
They call it an injector sleeve


From what I’ve read, the PCM identifies which cylinder is missing based on crankshaft acceleration. It basically takes the first derivative of crank velocity. If it detects a crank decel, it knows the angle and can deduce which cylinder missed. But as mentioned, it can’t differentiate between fuel/spark/etc

That injector fault though…check the wiring between the PCM and injector and if it checks out, I’d throw a new set of injectors in.

If it is due, I’d just do them anyway.


The pcm can usually pinpoint a problem with an injector feedback issue electronically, however it has no idea if it is actually opening and closing.

In order to detect a misfire in the ignition it has to calculate based on timing which cylinder I thinks is misfiring
This can take several drive cycles, and the code can be pending for some time

So typically a misfire cod that appears right away is usually injector related, at least that has been my experience with these engines.
The ignition is very stout and it is waste fire so typically you can move the misfire by doing some testing and switching of the wires from one cyl to the one it shares a spark with

Misfire codes USUALLY fuel, but not always. How quickly the code comes back and can you move the code to another cylinder by switching wires will tell the tale