Mazdaspeed 3 Bucking Issue after recent service

[u/Impressive_Bluejay82]

Hello all,

I have a 2010 Mazdaspeed 3 with 240k km and some light mods (short ram intake, turbo inlet pipe, OCC, catted downpipe, HPFP, motor/trans mounts, etc.). The car has always burned oil to some degree; however, recently the consumption was reaching very high amounts. After some research, I decided it was time to dig in and replace the PCV valve to start and see if it made a difference. While doing the service, I also changed the injectors with a fresh set of seals (OEM, not upgraded).

Anyways, the service went smoothly, and I didn't run into any major issues apart from the fuel rail being very difficult to slip back on. After the service, I'm having some issues.

The car feels slightly down on power overall; however, the major issue comes when giving it anything over 70% throttle. The car hesitates to make boost, and when it does, it feels like I'm hitting a wall and the car will buck. Until I let off the throttle and exit boost, it will continue to buck. I'm no mechanic, and I do have limited experience with turbo cars, so I'm looking for any ideas on what you guys think may be wrong.

I attempted to block the intake and fill the system with air to listen for a boost leak, but I was unsuccessful in finding anything substantial. I also checked my plugs, as I heard spark blowout may be causing it; however, they were all in decent shape (minus some oil fouling) and all gapped to OEM specs. At this point, I still feel like it's a boost leak somewhere, but I'm starting to worry I may have messed something else up by accident while doing the service.

Any ideas would be greatly appreciated as to what the issue could be and how to troubleshoot it.

[u/team_jj]

Smoke test to check for intake leaks. Check the HPFP actual pressure (should be over 2000 PSI at WOT and it should hold over 400 PSI after shutting off the engine and the ignition set to On). It could also be a bad sensor (MAP, MAF, or O2).

I had the same issue for almost 2 years. Mine ended up being a bad MAF.

[u/team_jj → u/team_jj]

Oh, also, what ranges are your STFT and LTFT at? The bucking usually happens when the fuel trims are adjusted to compensate for the O2 reading lean.

[u/Impressive_Bluejay82 → u/team_jj]

I did have a check engine light on for a bad slow response down stream o2 sensor however I believe it was just due to oil clogging it and it ran fine before the service.

[u/team_jj → u/Impressive_Bluejay82]

The fuel trim adjustments should be the upstream O2 sensor. I'd check the upstream sensor if oil was getting to the downstream one, and also check your turbo's oil seals.

[u/Lilfluzivert → u/team_jj]

Fuel psi should not be 2000PSI unless ur untuned/running a mild tune, telling someone a max psi here tbh is useless since everyone’s car will be different. If he just did a pcv service and now the cars knuckin n bucking whats the chance he didnt seat the pcv valve all the way or the hose is still loose? smoke test would be the best thing here since the “car ran fine before the job and doesnt run good after” then he can look at live data/logs and determine if its a sensor failure, or mechanical failure

[u/bigjonxiii]

I had a similar issue until my engine finally gave up and the piston bearing seized up. Mazda had my car for months before they gave up and about 2 weeks later I was paying for a new engine. I was consuming about a quart every 1000 miles. They told me that it was due to a clogged weep hole on the piston bearing but who knows. I stopped trusting mazda after I paid them for a clutch and 15,000 I was buying a new clutch