More Fiesta issues: misfires

[FiestaSTdude]

Ok, my car is testing my patience at the moment and I’m trying to figure out if I’m overreacting. After resolving the wiring/boost sensor issues I drove it for a couple days and it was fine. I reinstalled the cowl and fired it back up and immediately got codes for random misfires and misfires on cylinders 1 and 4. I drove it briefly and it felt fine so I cleared the codes and continued to drive it. I’ve been monitoring misfire count on my accessport and I’m getting lots more misfires than I would expect, like 200 or 300. I’ve filled up once since it noticed the issue with no change. Plugs are ngk 6509s with 15k and ignition coils are also ngk with 15k miles. Am I overthinking this and worrying about something I shouldn’t be? I plan to pull my plugs and check the gap and maybe replace the ignition coils. Any thoughts or advice?

 

[DEss]

Ok, my car is testing my patience at the moment and I’m trying to figure out if I’m overreacting. After resolving the wiring/boost sensor issues I drove it for a couple days and it was fine. I reinstalled the cowl and fired it back up and immediately got codes for random misfires and misfires on cylinders 1 and 4. I drove it briefly and it felt fine so I cleared the codes and continued to drive it. I’ve been monitoring misfire count on my accessport and I’m getting lots more misfires than I would expect, like 200 or 300. I’ve filled up once since it noticed the issue with no change. Plugs are ngk 6509s with 15k and ignition coils are also ngk with 15k miles. Am I overthinking this and worrying about something I shouldn’t be? I plan to pull my plugs and check the gap and maybe replace the ignition coils. Any thoughts or advice?

You can try swapping the coils for 2 and 3 to 1 and 4. Clear the codes and take a drive. If the codes indicate misfires on 2 and 3 then it's likely the coils. If the misfires stay on 1 and 4, then swap those plugs to 2 and 3. Reset the codes and retest.

 

[FiestaSTdude]

It’s been a minute, but I’m still getting these random misfires. They seem to happen primarily under high rpm low load situations. I swapped the coils and the misfire codes are still only present in cylinders and 1 & 2. That car runs fine except sometimes if I’m pushing it and run high rpms then the check engine light will start flashing and it will run rough. Also, when I monitor misfires on the accessport I notice a lot more than I would imagine is normal.

 

[FiestaSTdude]

This has been a while now, but I pulled cylinders 1 & 4 spark plugs

 

[FiestaSTdude]

Something else I should probably mention is that my short term fuel trims are fluctuating a lot. Long term fuel trims stay in the 4 to -4 range but I’ll see STFTs from-29 to 29. They don’t always fluctuate that much and they tend to be extremely negative more than extremely positive. Note that this happens almost every time I drive, not just when the misfiring gets to the point where I can notice it.
I’ve been very lazy about looking into this because 98% of the time I don’t notice anything. I’m going to see if I have new 6509s and if so I’ll throw them in and see what happens.

 

[FiestaSTdude]

So during our process of resolving the wiring issue, we had swapped out the pcm for one from a junkyard car. Because the misfire occurred after that we suspected it might have caused them. Today we swapped the original pcm back in to my Fiesta. I’m now seeing a lot less misfiring, 40 misfires in 30 minutes of driving instead of 200-500. I do still seem to have a single misfire occur fairly often if I accelerate lightly in 5 or 6 gear. Is that normal/something I should be worried about in y’all’s opinion? I’m trying not to let my accessport become an anxiousport lol I’m just very conscious of misfires at the moment.

 

[bshanahan14rulz]

Mine misfires when I accelerate lightly in 5th or 6th. I don't feel it, though I'm not sure I would know what it would feel like. I just see the misfire counter go up by one. And "lightly accelerate" means me touching the gas about as lightly as possible.

I generally get 5-15 misfires in total for my 40-minute commute, depending on the weather for some reason. So, I don't know if it's "normal", but here's another owner who has observed the same symptoms.

Do you have the clunky transmission that clunks and clacks when shifting 1-2? I have read different things, from "that's just how they sound" to "your output shafts need to be replaced", but I'm curious if the clack might point to some slack in the drivetrain, which may cause false positive for a misfire due to maybe affecting the rotational velocity of the drivetrain enough to make the computer think it's a misfire.

 

[NATYPE]

Big LTFT swings sound like EVAP harness to me. Mine is currently bad / going bad and it causes the same bahaviour. And smaller swings you can feel and see (watch AFR) as surging in any gear mostly when light throttle inputs are concerned. If you happen to accelerate in a bad moment I imagine that would cause some not great behaviour. Otherwise I guess I'd be checking the plug gaps or swapping them entirely? I'm at 12K miles on mine and I think I'm starting to see some wear signs through increased negative corrections. Just observations from my own car and AP though.

 

[FiestaSTdude]

Mine misfires when I accelerate lightly in 5th or 6th. I don't feel it, though I'm not sure I would know what it would feel like. I just see the misfire counter go up by one. And "lightly accelerate" means me touching the gas about as lightly as possible.

I generally get 5-15 misfires in total for my 40-minute commute, depending on the weather for some reason. So, I don't know if it's "normal", but here's another owner who has observed the same symptoms.

Do you have the clunky transmission that clunks and clacks when shifting 1-2? I have read different things, from "that's just how they sound" to "your output shafts need to be replaced", but I'm curious if the clack might point to some slack in the drivetrain, which may cause false positive for a misfire due to maybe affecting the rotational velocity of the drivetrain enough to make the computer think it's a misfire.

That sounds exactly like what mine does. I get about 5-10 misfires in my 25-30 minute commute. Since both our cars do it, I’m going to assume it’s fine lol.
My transmission doesn’t make much noise but 1-2 is jerky if I don’t let off the clutch just right. I’ve always blamed rev hang and the heavy flywheel. To be honest, that jerky shifting is my biggest issue with the car. It’s just annoying.

Big LTFT swings sound like EVAP harness to me. Mine is currently bad / going bad and it causes the same bahaviour. And smaller swings you can feel and see (watch AFR) as surging in any gear mostly when light throttle inputs are concerned. If you happen to accelerate in a bad moment I imagine that would cause some not great behaviour. Otherwise I guess I'd be checking the plug gaps or swapping them entirely? I'm at 12K miles on mine and I think I'm starting to see some wear signs through increased negative corrections. Just observations from my own car and AP though.

It could be related to that, I’ve had evap codes for months now lol. Do your STFTs stay pretty consistent? Mine will go as low as -28.

 

[robine]

Hello, were you able to solve this? I‘ve been having the exact same problems, I replaced the spark plugs and the ignition coil and the car is still misfiring.

 

[TyphoonFiST]

Hello, were you able to solve this? I‘ve been having the exact same problems, I replaced the spark plugs and the ignition coil and the car is still misfiring.

Every single car misfires to a certain Extent* Some manufacturers set the tolerance higher or lower in order for the check engine light / MIL to illuminate. If your car doesn't misfire or knock at all its Lawn art with an artificial window

 

[FiestaSTdude]

Hello, were you able to solve this? I‘ve been having the exact same problems, I replaced the spark plugs and the ignition coil and the car is still misfiring.

My problem ended up being the PCM. I had replaced the original pcm trying to fix something else and the junkyard pcm I got had issues.

 

[bshanahan14rulz]

That sounds exactly like what mine does. I get about 5-10 misfires in my 25-30 minute commute. Since both our cars do it, I’m going to assume it’s fine lol.
My transmission doesn’t make much noise but 1-2 is jerky if I don’t let off the clutch just right. I’ve always blamed rev hang and the heavy flywheel. To be honest, that jerky shifting is my biggest issue with the car. It’s just annoying.


It could be related to that, I’ve had evap codes for months now lol. Do your STFTs stay pretty consistent? Mine will go as low as -28.

I don't feel like my 1-2 is jerky, but this is the only manual I've ever driven, and I try to let the clutch out when the RPMs are where I think they'd ought to be, I think some call this granny-shifting? I'm gonna assume that our level of misfires is "normal" too, and just focus on my fuel trims.

I did start monitoring my STFT and LTFT, though not writing it down or anything. I don't recall my LTFT, but my STFTs vary WILDLY, I saw -28 just this morning. I think mine's just related to the typical Ford Evap BS. I've already replaced the solenoid, but getting different errors now which may be pointing to a clogged canister or something that connects the fuel tank to the canister. Because of the type of damage I saw in the solenoid, I don't want to keep buying parts until I know what the actual cause is.