Weird misfire issue

[BitchinCorolla]

Hey guys,

I’ve got a real confusing misfire issue going on, hoping to get some help. I’ve always had a minor misfire that occasionally goes on during idle but it’s been a non issue so I ignored it. But I was on a 4 hour drive today and the misfire starting getting really bad. Misfiring at idle, misfiring when accelerating in neutral, and sputtering under load when driving. I limped along the highway and stopped at a rest stop and it got better. Still stumbling under any throttle but good at cruising. An hour later it changed again, misfiring a lot at neutral but fine under acceleration and load for the most part. I’m pretty lost at where to start, and I have to drive the car back on Sunday so I’d like to fix this before then. I have replaced the following relatively recently:
Fuel filter
Spark plug wires
Spark plugs
Not sure if anybody has had an inconsistent misfire like this, maybe some of the symptoms point to something specific, please let me know. Thank you.

 

[cobrajeff96]

Fuel, air, spark.

It's easy to test ignition components in these modular overhead cam motors with coil packs and the long wires. Just pluck the plugs and boots out of each bore one at a time, unhooking the fuel injector wire for that cylinder, and make contact with the plug's ground strap against some bare metal (you can very carefully jump a long wire to maybe make this process easier) while someone cranks the motor with the key. You can also just disable the fuel pump and dry crank the motor by using the ignition key as a pick to pull up on the red button inside the trunk (driver side rear, right next to the tail lamp) to lock out the safety intertia switch and the fuel pump should be disabled. Test each plug, you should see a big ass spark for each one.

I would not recommend pulling injectors because a lot could go wrong.

I'd say start with spark testing, then go from there. I've experienced it myself a few times when buying replacement ignition components for my old '96 4v motor. They just don't make 'em like they used to anymore. When you buy those things for these cars, especially in the aftermarket, it is quite literally hit or miss.

 

[96blak54]

Be sure no moisture in the sparkplug holes.

Sparkplug wires are very finicky in them sparkplug holes too. Pull the plug wire out and shove a sparkplug into the wire boot to be sure it engages and not completely swallow the plug.

 

[RAU03MACH]

Be aware
The spark plugs brand new in a box can also cause misfire
Im just giving you a problem in recently ran into
I had done a tune up on my truck 1st round
Bought a set of motor craft from o'riley
Second round had to go back in and check every thing thought mabe a coil
3 rd round put the new fox tester on the truck
It had a total of 30 misfire after I changed the plugs
4 th round cleared the codes drove it with fox tester connected on it and while driving I could see 4 out of 8 plugs misfire
5 th round bought a new box of plugs from ford
Problem fixed
Just saying that new plugs out of a box can be problems to