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I have a Ford Fiesta SE from 2012, and I've had this issue for months that feels like a Damocles sword above my head. Mechanics can't pinpoint it, I'm trying here.

I have a massive torque dip around 1500-1700rpm - sometimes I drive through it and I can feel it without it being much of an issue, sometimes I shift up and end up right in that range and it's killing my acceleration entirely and it takes time to recover unless I shift back up - which has been dangerous at the beginning (now I know, but still). Some other times it's fine (though rarely when the car is already developing significant torque)...

Doesn't happen anywhere else.

I've given up on clearing the check engine light, as it comes on very quickly; reports are more or less this - misfires come and go (sometimes random, sometimes 1, sometimes 4), but the MAF is always there and the fuel leak very often. First time I see battery voltage, might have been when I briefly unplugged the battery recently to reset my radio's BT. enter image description here

Note that the car has a rough idle and is really acting its weirdest when I am low in fuel (Below quarter, though I haven't been there in a while), but the above still stands when full. I must admit I used to run it to the last drops more often that I should have.

Any ideas?

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    Welcome to Motor Vehicle Maintenance & Repair! Sep 11, 2023 at 19:32
  • I agree with MTA here ... you need to fix what you know is wrong first, then concentrate on what you don't. One of the first things which comes to mind about you saying there is a "torque dip" is, I'm assuming you are doing everything by seat of the pants. IOW, you don't really know if there is a torque dip, you're assuming that's what's going on. Just like what MTA stated, I'd get away from that line of thinking and work on fixing what you can fix. Also, providing the exact codes would be a big help, but that may be another question. Sep 11, 2023 at 19:32
  • I'd gladly do that but there is nothing I know is wrong. The codes don't point to anything in particular, in isolation or combined. At least not to me nor my mechanic, maybe you'll all see it straightaway. I'll put them here tonight. Although there is no easy way for me to measure the torque dip, I can say with 100% certainty the torque plummets in an instant if I find myself shifting up right in that range: I basically buy myself a 0g horizontal experience for a moment, if not a negative acceleration. I may not know how much the torque dip is but there's one & it can be massive. Sep 11, 2023 at 19:51
  • Updated with the OBD diag report Sep 12, 2023 at 4:09
  • Had an similar thing ages ago: Turns out the insulator of a spark plug was broken. Dip only manifested itself on certain RPM ranges. That ignores the MAF issue, but controlling the spark plugs is always a good idea.
    – Martin
    Sep 12, 2023 at 9:41

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EDIT: This answer was written before engine codes were supplied.

I’m not going to answer the question “What causes my massive torque dip” because (1) you have not provided essential information about specific engine codes and (2) you are knowingly driving a broken car (your check engine light is nearly always on) but you are not taking effective steps to repair it.

Fix all the problems that are causing your check engine light to come on, and your massive torque dip will probably resolve. If it does not, at least you will know what is good so you’re not chasing your tail and guessing or relying on hunches from random strangers on the internet.

First and foremost, you need to find a mechanic whose mantra is diagnose, diagnose, diagnose, then repair. You need evidence-based diagnosis and repair, not hunches.

You need to get past the false assumption that a particular engine code means that a particular part needs to be replaced. Sometimes it’s true, but often it’s not. You mentioned a MAF code. Sorry, no such thing. Did you mean P0101 Mass Air Flow Circuit / Performance Malfunction? Sometimes that means that the MAF is bad. Not always. The same code can be caused by a melted wire or corroded connector, a vacuum leak, a hole in an air duct, a dirty air filter, a clogged cat or a dent in an exhaust pipe from driving over a branch. If you replaced the MAF sensor but you still have the code, that wasn’t the problem and you wasted your money.

Diagnosis is not free and it’s not cheap, but in the long run it’s way cheaper than replacing random parts on a hunch, and infinitely cheaper than giving up on a repair and junking a car that “can’t be fixed” because no one spent the time to do a proper diagnosis.

Your car can be fixed. It requires a methodical approach to run down and repair each code, one at a time. When the mechanic tells you that X engine code means that Y needs to be replaced, don’t give permission unless he or she can guarantee that this will fix the code or the repair is free. That will separate the facts from the BS right away. If the mechanic isn’t diagnosing but just guessing and won’t give a guarantee, you need a better mechanic.

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  • I appreciate you answering, but you are actually assuming I blindly replace things based on hunches. I'm not asking you to fix it, I'm asking for leads I can investigate with my mechanic because at the moment there is nothing that stands out from all the possible contributors. As I said the "MAF code" was just me trying to remember the codes I had obtained a while back - I can give a complete report. Sep 11, 2023 at 18:49
  • Finally I am not driving my car "not taking steps to fix it": first, I only drive it because we have established it was safe to do so (wouldn't have done so with faulty brakes), and second taking steps to fix it is what I've been doing for weeks if not months. No one knows locally, so I'm asking for stranger's opinions as a last resort. My mechanic doesn't fix things if he's not sure it's not that, but the drawback is that nothing's moving with this. Sep 11, 2023 at 18:49
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    @MisterMystère Hey, if my approach to your question made you a bit defensive, that's not my intention. I know you're not a dumbass -- I remember your name under some very good answers in electrical engineering. You should visit here more often and contribute on electrical questions. All I'm saying is that you're going about this backwards. Forget the torque dip and fix whatever is causing engine codes. Everything, a permanent fix. There's no point in asking opinions on torque dip until your car is 100% code free. Your mechanic has not achieved this.
    – MTA
    Sep 11, 2023 at 19:08
  • @MisterMystère You need a better mechanic. If that's not going to happen, come back with a new question listing of all codes and symptoms for ideas to fix the codes, not necessarily the torque dip. Chances are it will resolve on its own when all the codes are addressed.
    – MTA
    Sep 11, 2023 at 19:08
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    @MisterMystère Dang it, I really wish you had made a new question as Paulster2 and I had both recommended. A new, fresh question with no distracting comments and tedious answers would definitely get more attention here. You can still salvage this by editing to remove what you've just added before anyone takes the bait and compose a new question giving codes and symptoms. It would help if you include short term and long term fuel trim readings at the same time, because that may reveal a fertile ground for diagnosis.
    – MTA
    Sep 12, 2023 at 11:58

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