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Discussion Starter · #1 ·
Hi all, I am new to the forum, and out of frustration at not being able to diagnose the problem I have come for help to the hive.

I have a Mazdaspeed 3 with a rebuilt and resurfaced engine with 2000 miles on it.
Bought it with an engine knock, and managed to fix that with CorkSport Injector seals. However after getting it up and running I have noticed that the car bogs down, and runs very rich at 5k rpm, and sometimes even when I take off from stoplights @ 2-2,5k rpm.
I will post some logs shortly that I took with VersaTuner (I have tried to flash the tune, -factory tune, economy tune [to try to reduce the afr] and base model 91 octane tune)

So far, I have replaced the spark plugs, loaded a tune, replaced fluids, checked compression and timing. All my tests came out great, timing was on point and so was the compression. I have ran out of ideas. The afr is 29 at idle, 12.3-13.4 at load, and reached a low of 9.0 at 5k rpm (and violently rocked the car back and forth with just loss of power)
Also my friend noticed while driving behind me, that the car produces a significant amount of black smoke when it bogs down.
 

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2013 Mazda 3 i Hatchback
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Based on the symptoms, it sounds like a loss of boost or an exhaust obstruction, which throws the A/F ratio rich. But that's a guess based on limited information. Here are some more questions for you, some of which will require a OBD scanner with live data:

  1. Does it only go rich and bog down at 5k rpm when under load, or will it bog down just revving it in neutral?
  2. What do the fuel trims look like, particularly the short term trim when it bogs?
  3. Is the money light on, and is there any stored codes in it?
  4. When it bogs down, what happens to the boost/manifold pressure? How about just before? If you had a boost leak or a wastegate/blow-off valve that isn't staying shut when it should, that could be causing your symptoms.
  5. Was the turbo rebuilt/replaced when the engine was rebuilt? A blown engine can do bad things to a turbo...
  6. Are there any mods to the engine (other than the tune)? Can you put the tune back to stock and see if it makes any difference? If you have the ability to restore things back to stock (such as putting back the stock intake instead of a short-ram) that can help isolate the problem.
  7. Have you tried cleaning the MAF sensor?
  8. Exhaust/cat plugged? Bang lightly on the cat and exhaust, listening for anything rattling inside...
 

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Discussion Starter · #4 ·
Hi, thank you very much for your reply.
1. The problem only occurs under load, neutral is fine, it also doesnt happen when I accelerate slowly. Only when I do a full throttle pull. I can very slowly get up to redline in every gear without bogging down if I increase throttle very slowly.

2. Will answer the log based questions when I get home from work and review them properly.

3. Have the check engine light on, and the only code is P2188 “System too rich at idle bank 1”

4.Need to double check

5. The previous owner did the rebuild, and I can only imagine the turbo wasnt replaced, only the internals were new.

6. The car is completely stock, besides injector seals. I have also reset the tune to factory tune with no changes

7. Now that I think about it, I have done the seafoam spray clean but not a MAF clean specifically

8. Will check the cats soon and get back to you

Thank you!
 

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Discussion Starter · #5 ·
2. The Short term fuel trim fluctuates rapidly from -22% to -29% when it bogs down. But during the random clean pulls that happen rarely it stays on -25%

4. The boost mirrors the rpms almost perfectly during all pulls. Boost goes up, rpms go up, let off the throttle boost goes down ect.

8.Checked the exhaust and the cats just then, no rattles, and doesnt seem plugged.
 

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Thanks for following up with more info. All too many new members with their first post don't follow up...

Anyway, the short term fuel trim doesn't sound correct. Your saying that even when the engine doesn't bog down the fuel trim is -25%? That doesn't sound right to me. I don't have a speed3, so I can't test that myself. Anyone out there want to see what happens when you floor it in a speed3 and check me?

My understanding is that fuel trims can vary, short term will vary quickly with changes in load, rpm, throttle position, etc. Short term is also rapidly responding to what the O2 sensors are reading, and that under rapidly changing driving, it can spike to high values, but that it should not stay at high numbers for long periods and throughout a wide range of revs. Long term fuel trims on a healthy engine should be within +/- 10 and ideally very close to zero.

Seems like either the MAF is telling the computer that it's getting more air than it is (unlikely given the boost seems consistent), there's a boost leak somewhere (again, unlikely since it's holding boost), the injectors are squirting more fuel than is being commanded, or the O2 sensors aren't reading correctly (possible, but you'd likely throw a code for it). Given that it seems like the trim is pinned at -25, and you just had the injectors out to do the seals, I'm wondering if the injectors aren't having a problem.

When you pulled the plugs, were any of them different from the others? Wet, oily, caked with carbon or with a burned up electrode? Have you looked at the plugs since the bogging down started? Just wondering if the problem is isolated to one or two cylinders. Also, if it's squirting extra fuel, you might be experiencing fuel dilution of your oil. Does your oil smell like gas?

Do you have a way to see misfires in your live data? If so, do you get misfires when it bogs down? Seems like it should be missing given that you're losing power and blowing smoke. Of course, a cylinder with a bad injector might be misfiring because it's too rich, or a good one might misfire because the fuel trim has it too lean to fire... :)
 

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Discussion Starter · #7 ·
Thank you again for responding.
So, the spark plugs themselves were all the same, clean, however back when I pulled the injectors, I noticed 3 of them were completely black, including the injector ports, and one was completely clean (including the port). I completely forgot about that as I thought the new seals would fix that issue as I cleaned everything and then put the new seals in.

I will upload a video to youtube tonight and send the link here so you can see what happens when I do a pull. The car sounds like its backfiring rapidly, and lots of black smoke comes out the exhaust, almost like a diesel. So Im not sure if its a result of misfiring.

As per my oil smelling like gas, yes it totally did when I did my oil change, I was alarmed at first but then remembered I put seafoam cleaner into the oil to clean the engine internals (followed the instructions) and dismissed the issue because I thought the seafoam could be a culprit. But yes, oil smelled heavily of gas.

I will be doing another proper log and pay attention to the fuel trims to see if I messed up on the previous logs. Will keep you updated
Thanks again 🙏
 
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