Misfire upon half throttle acceleration

[Smurfysi]

Hey guys. I got a 2018 civic si and I have the following mods, injen intake, maperformance catback, and boomba bov. Just about a week ago when I put gas in my car, I noticed that when I was accelerating I was only building 13-10 psi in 3rd gear. And I just put a new tank of gas in my car yesterday and now I’ve noticed a spudder/misfire when accelerating at half throttle upon the first 5-10 minutes of driving and sometimes after that. I’m just asking if you guys have had the same issue or if I should go to the dealership. Would they still warranty me with the parts on the car?

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[Royal_Purple_Oil_Filter]

Certainly the dealer is going to deny you warranty, especially if mods are engine related.

 

[Matthyahuw]

is it a full BOV or BPV?

could be something simple like bad gas, or plug change...

 

[Overeazy]

Betting on the bov causing your issue they're known to be trash for these cars..Start taking them off starting with the bov, then the intake. They will probably let the exhaust slide.

 

[Smurfysi]

Betting on the bov causing your issue they're known to be trash for these cars..Start taking them off starting with the bov, then the intake. They will probably let the exhaust slide.

Just took off the bov and disconnected the battery and reconnected it. No CEL or warning lights at all but still have the slight sputter and misfire. Took it to Honda and scheduled an appointment. But I noticed that it mainly does it right after start up. Whether the car is cold or has been running for 30 minutes and it was only off for 5 minutes and still warm

 

[Overeazy]

Probably a good idea to have Honda take a look before you drive it more. If it was a miss fire the check engine light would flash so I think you're safe there. I think the bov screwed up your air fuel ratio (too rich causing sputters when the engine is cold) and the ECU probably needs some time to re-learn. Just a guess I'm not a mechanic. Hopefully it didn't damage your maf sensor I think those are expensive.

 

[Smurfysi]

Probably a good idea to have Honda take a look before you drive it more. If it was a miss fire the check engine light would flash so I think you're safe there. I think the bov screwed up your air fuel ratio (too rich causing sputters when the engine is cold) and the ECU probably needs some time to re-learn. Just a guess I'm not a mechanic. Hopefully it didn't damage your maf sensor I think those are expensive.

Thanks I don’t think it would damage my MAF sensor seeing how everything’s happening after it. Only thing I can think of is probably fouled spark plugs

 

[Doc_Mello]

Yeah, please keep us updated. I would think that, with fouled plugs, the performance would degrade over time, not just suddenly happen.

Since it started after refueling, it sounds to me like you didn’t put in the correct octane fuel.

 

[caspar21]

bad gas maybe?
if it gets worse replace plugs. run it right down, possibly fuel filter(if it got plugged up).
run it through or drain it. yur call.

with the direct injection and hi pressure pumping system it can get messy quick. walk carefully. fouled injectors and messed pump is a real possibility(assuming my guess is correct and its bad gas).

 

[Overeazy]

Impossible to say without more info, the Honda dealer can tell you exactly what it is. But they will question you about the intake and probably try to blame the problem on that first. The bov just shouldn't be on the car there's threads here about them causing the motor to run rich, yep we want turbo noises too. https://www.civicx.com/threads/how-safe-is-the-boomba-racing-blow-off-valve.36280/

 

[Lifesabeach]

I have this on mine, UK based. Its been to the dealers 4 times and Honda also got involved and the result is they cannot find anything wrong, I hope you have better luck then me please keep us posted.

 

[Smurfysi]

Update: Honda says the car is leaning out pretty hard. So they’re putting a stock air box back onto the car and seeing if that stops the issue. If it does, they’re not going to warranty the vehicle

 

[Smurfysi]

Final update: Honda says it was my exhaust. They put the stock one back on and it stopped sputtering. They put the modified exhaust on and it started to do it again. It’s reading rich conditions and making the car run lean for some odd reason. So my next step is to get a tuner for my car and tune it shutting off the o2 sensors and forcing it to run on a set map instead of adjusting itself for stock power. I’ll let you guys know more once it’s tuned

 

[Troy Jollimore]

That’s odd. Usually an exhaust leans things out on it’s own. Does it have any mountings for O2 sensors on it? The other thing you can try is put the stock airbox back on and see if the problem goes away. It could be a tandem thing.

 

[herox]

That’s odd. Usually an exhaust leans things out on it’s own. Does it have any mountings for O2 sensors on it? The other thing you can try is put the stock airbox back on and see if the problem goes away. It could be a tandem thing.

Surprised no one has said this but a few people have had issues with the Injen intake: https://www.civicx.com/threads/what-the-hell-is-so-wrong-with-the-injen-cai.26539/

OP did they put the stock airbox back on?

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