Hello, I recently bought a 2015 Fiesta ST with about 100k miles. I love the car but as I try to learn more my anxiety is skyrocketing. It has an injen intake, an exhaust that I don’t know the brand or how far it goes (I replaced the passenger cv Axel and forgot to inspect the exhaust and turbo), and who knows what else. I think the rmm is aftermarket. I’m concerned it has a tune that I’m unaware of. There no access port though.
The reason I’m so concerned is because I’m getting a pulsing from the turbo in 3rd around 3k rpm. The car surges and the BOV goes past psst psst psst. I can floor it or let off the throttle and it smooths out. Am I just lugging on it too low of rpm? Is my wastegate bad? I just replaced the MAP sensor that is on the left hand side at the top in front of the engine and that didn’t help. Could it be a fault in the fuel system? I have no CEL lighting up.
Im just stumped, I’m not having luck with google or YouTube as far as finding people with a similar issue. I don’t even know what terms to use as I’m new to turbo cars.
I had something similar happen last year. I’d be cruising on the highway around 55-60 mph in fifth gear, and it would just stutter and not accelerate. I replaced the spark plugs and coil packs, and that seemed to fix it. It’s been nearly 15K miles since, and no issues.
I totally get the hesitation with mods and wanting to make sure everything’s right. Pulling a plug to see what the original owner used is a great start—you’ll get a sense of what’s been installed.
As for going one step colder with the plugs, it’s generally okay, especially if you’re running higher performance or pushing the engine harder. But if your car’s not tuned for it, it might not be necessary and could affect fuel efficiency or performance at lower temperatures. It’s best to match the plugs to your current setup or consult with a mechanic if you’re unsure.
It’s clear you care about your car, and doing what’s best for it is always a good move!
I’d highly recommend getting an unmarried Accessport (AP). It’ll let you check the tune, as well as monitor fuel corrections and misfire counts. Pull a spark plug and see if they’re one step colder, then go from there. Also, check if you have an upgraded intercooler—this is a big sign of an upgraded tune. Keep us posted, and welcome to the group!
I got a used 2019 with an intake, exhaust, and a tune. I had some weird idle surges with regular 91 octane from QT, but after switching to a different fuel, it runs much smoother now. After changing the oil and spark plugs, it’s even smoother.
Don’t worry, these cars are easy to work on (so far) and parts aren’t too expensive (so far…). They’re pretty durable.
I’d recommend doing basic maintenance, running a quality fuel injector cleaner (or cleaning them the old-fashioned way), and maybe trying premium gas from Shell or Murphy, or whatever you have locally. My car seems to like those better than QT’s premium for some reason.
It could be an issue with the wastegate or BOV, but I’d start with the simpler stuff and see what others suggest. I haven’t had any problems with either so far.
You’re right, an AP isn’t needed to run a tune once it’s installed, so you might have a tune, but it’s tricky to confirm without checking the actual ECU.
From what you’re describing, it sounds like the car might be having trouble maintaining boost pressure. If the car is tuned, and there’s a stock BPV or a BOV that needs maintenance, that could be why you’re hearing it vent off despite being on the throttle. It might be worth checking or servicing the BOV/BPV to see if that’s causing the issue.
Got the plugs and coil packs ordered! Whoosh is definitely hitting hard with that price of $206 shipped. Hopefully, they’ll make a noticeable difference once installed!
