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Discussion Starter #1
Hi everyone. I recently purchased a 2014 focus st and have done some basic stage 1 mods to it. Intake, RMM, muffler and resonator delete. I also have a stratified tune for the pops and bangs. Recently under WOT I’m experiencing constant loud backfires. If I ease into power it doesn’t do it until I’m WOT. I’m not really sure where to begin with figuring this out. I’ve tried to retune and went back to Cobb stage 1 but it’s still doing it. If anyone could give me any tips on what to monitor and where to begin I would appreciate it.
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Check your plugs. If it's not burning all the fuel due to the plugs being fouled or gapped too much, it could cause it to be sending raw fuel into the exhaust, which could easily ignite from a hot catalyst.

ETA: Also sounds like it's not doing it until it goes to open loop mode for injector firing from your description. (Only doing it at wot)
 

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What he said...

And stay out of WOT until you do or you may end up with something like this:



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My car does this on occasion from time to time on the stock tune, stock plugs, etc, but ONLY when I let off to shift, NOT during acceleration. My advice would be, before you go messing around with the plugs, just reflash the car to stock tune and go for a run, if it still does it, then you have an issue, if not, its probably a side effect of the snap and pop tune as dumping fuel into the exhaust when you let off is essentially how it works...

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Discussion Starter #5
Thanks for all the feedback so far. I'll go back to stock tune tomorrow and get back to you guys if the problem is still there. I did run the tune for a couple weeks without any problems, but this just started out of nowhere.
 

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How many miles are on the plugs? If they haven't been checked in 15k or so, you should pull one, at least, and check the gap on it.
 

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Do you feel any loss of power when it backfires? I would definitely check and replace the plugs regardless and gap them to .026
 

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Finally fixed. Some new spark plugs did the job
I’m having a similar issue with my stratified tune. Everything seems fine till go wot and hear some popping and a tiny bit of power loss almost likes sputtering. I do not have any codes and runs fine on stock tune which I have switched back to now. I doubt my plugs have ever been changed so I ordered some ngk 1-step colder plugs and going to put them in and give that a try. Stratified takes forever to answer so I have to troubleshoot myself in the meantime.
 

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Could I get some more info on this picture lol?
How much do you want?

This is a photo of the engine that was pulled out of my ST back in August.

Unfortunately all we have is theory and wild speculation about exactly what happened, but I think it had a weak connecting rod in cylinder 4 that let go when the car started backfiring.

The main difference here is that it didn’t blow under WOT... it let go at about 3800 during a 3-4 gear change.

I chimed in here because when the tech was investigating the cause of the failure, for warranty repair, pulled the plugs they were gapped to .040-.043 and the ECU didn’t report any excessive knock up to the point of failure.

That being said, it’s my theory that the poorly gapped plugs caused the backfiring, which then caused an already weak rod to fail... the end result of that failure is what you see in the photo.

I might be wrong, but plugs are cheap, $30-$50 a set... a new engine, not under warranty, is roughly $7,000-$12,000.

BTW... I got lucky. Mine was replaced by Ford under the power train warranty.


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W
How much do you want?

This is a photo of the engine that was pulled out of my ST back in August.

Unfortunately all we have is theory and wild speculation about exactly what happened, but I think it had a weak connecting rod in cylinder 4 that let go when the car started backfiring.

The main difference here is that it didn’t blow under WOT... it let go at about 3800 during a 3-4 gear change.

I chimed in here because when the tech was investigating the cause of the failure, for warranty repair, pulled the plugs they were gapped to .040-.043 and the ECU didn’t report any excessive knock up to the point of failure.

That being said, it’s my theory that the poorly gapped plugs caused the backfiring, which then caused an already weak rod to fail... the end result of that failure is what you see in the photo.

I might be wrong, but plugs are cheap, $30-$50 a set... a new engine, not under warranty, is roughly $7,000-$12,000.

BTW... I got lucky. Mine was replaced by Ford under the power train warranty.


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What tune were you using? And what modifications were done to the car?
 

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W

What tune were you using? And what modifications were done to the car?
I’ve been using a full tune from Justin @Freektune for over 2yr with absolutely no issues, and I’ve been Stage 3 since early ‘17 with CAI, Depo 3.5” FMIC, 3” stainless exhaust, catless DP, c-Pe stage 2 RMM...


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I’ve been using a full tune from Justin @Freektune for over 2yr with absolutely no issues, and I’ve been Stage 3 since early ‘17 with CAI, Depo 3.5” FMIC, 3” stainless exhaust, catless DP, c-Pe stage 2 RMM...


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And they replaced your engine under warranty in that condition?
 

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And they replaced your engine under warranty in that condition?
Yes. There were no internal modifications to the engine that would cause the failure. (I.e: balance shaft removed, low mass flywheel installed, WMI installed, alternate fuel rails, non-oem injectors...)


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Yes. There were no internal modifications to the engine that would cause the failure. (I.e: balance shaft removed, low mass flywheel installed, WMI installed, alternate fuel rails, non-oem injectors...)


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Hm, I thought tuning a vehicle from Ford voided all warranty?
 

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Hm, I thought tuning a vehicle from Ford voided all warranty?
If the failure can be directly attributed to the tune, they will deny the warranty claim.

I was sweating it because they spent quite a bit of time analyzing the ECU data before making the decision to fix my car.

I almost ended up with a $12,000 bill...


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If the failure can be directly attributed to the tune, they will deny the warranty claim.

I was sweating it because they spent quite a bit of time analyzing the ECU data before making the decision to fix my car.

I almost ended up with a $12,000 bill...


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If the failure can be directly attributed to the tune, they will deny the warranty claim.

I was sweating it because they spent quite a bit of time analyzing the ECU data before making the decision to fix my car.

I almost ended up with a $12,000 bill...


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Wow, this gets me scared doing any modifications to my car. Good thing I’m putting new plugs in it today since I had an issue like this when I applied the tune. Feel like I’m going to regret using a tune again due to these forums lol
 

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Wow, this gets me scared doing any modifications to my car. Good thing I’m putting new plugs in it today since I had an issue like this when I applied the tune. Feel like I’m going to regret using a tune again due to these forums lol
Don’t get gun shy with your mods. Just do good research, and work with reputable tuners.

My car had an internal issue that wasn’t fully realized until it started backfiring. I’m just glad it failed at 55k miles instead of 65k.


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Don’t get gun shy with your mods. Just do good research, and work with reputable tuners.

My car had an internal issue that wasn’t fully realized until it started backfiring. I’m just glad it failed at 55k miles instead of 65k.


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Wow that made me feel better. I guess your problem wasn’t due to tuning anyway. I’ve been recently checking everything out on my car including many stock tune datalogs just to make sure the tune was the problem lol.
 
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