Heavy misfire under load

G

Gabriel Buscema

Greenie N00B Member
Hey guys! I need some help. My car stutters/chops/misfire under load.

Here is some information about my car:
2007 mazdaspeed3
Engine was rebuilt 3 months ago (bent rod lmao)
FBO, BNRs4, middle of getting tuned with Justin using versatuner

Here's a further explanation of my issue:
When slowly increasing rpm of the car (like 10 percent throttle) the car acts and drives fine and idles like normal
When you give it any more than 10 percent or any load, it suddenly starts "chopping" and misfiring
Will throw an occasional p0300 code but it's rare and when I'm REALLY fucking with it

Now here's what I've tried already
Replaced plugs
Rotated a new coil through all 4 cylinders
Swap in 4 used coils
Compression test (170 on all 4)
Checked grounds
Added an extra ground wire from the hpfp to the chassis
Verified spark in all 4 using a coil pack tester
Verified fuel pressure is good
Verified prv is working
Cleaned MAF
Swapped back in stock map sensor
Verified it is in time
Replaced crank sensor and cam sensor
Took an oscilloscope to the injector plugs (as per Justin's recommendation) and verified a pulse to all 4 injectors from the ECU
There might be more that I cant remember right now
This is my daily so the sooner I can get it running the better
Thanks!
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It almost sounds like it's getting too much fuel. Like if you try to floor a car with a carburetor before it's warmed up

What size intake do you have?
 
Raider said:
@Gabriel Buscema Just saw this. If you sourced the plugs on Amazon, that could be why. They are fakes. Also check plug gap. .026 is ideal. Oem coilpacks only.
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It was off a part out car, so they are confirmed OEM. And like I (might) have mentioned I rotated through a brand new single one as well
Plugs were from the local O'Reilly's
 
Easter Bunny said:
It almost sounds like it's getting too much fuel. Like if you try to floor a car with a carburetor before it's warmed up

What size intake do you have?
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3.5 inch damond motorsport intake, the MAF is calibrated and was working before this issue suddenly popped up
Also I'm getting no rich or lean codes, just the random misfire only on startup
Also threw a smoke machine on the intake and there are 0 boost leaks
AFRs looked fine too I think? Idk id have to check back through the log lol
 
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What has Justin said about the logs of this? Probably good to upload here.
 
While mine was being tuned by damond also with VersaTune. Found that at the upper end of fueling flows for IDC max that my old Hpfp internals would fail to have maximum sustained pressure. So I needed to halt tuning. I replaced HPFP internals and a full teardown cleaning of PRV. IDC % would climb but was leaning out from logs. That was the cure.
Please post logs, especially ones that you send to Damond for fine tuning of your specific tuning needs.
 
Raider said:
What has Justin said about the logs of this? Probably good to upload here.
Click to expand...
Besides testing the ECU with an oscilloscope, Justin hasn't said too much. Here are the logs that I sent Justin
Recently I pulled injectors and I found that
1. They were all super dirty
2. previous owner only put aftermarket seals on 3 of the injectors?? not 4??
Justin basically said one of my seals was defiantly blown and could be the cause of misfiring
The injectors are currently on their way to SP63 for their cleaning and flow testing, and will also redo all the seals as well
IMG_20240829_170621892.jpg 5b22db79-4da0-4c99-9173-255cdf109aeb.jpg
 

Attachments

Alright guys, after 3 months of the car being down, injector cleaning and new seals not working, and not even the dealer figuring out what's wrong, I just fixed the issue
Turns out, it was the ECU the whole time!
I guess I did the oscilloscope test wrong because it was sending a pulse to my injectors on startup, and I couldn't test the injectors while the car was running due to the tmic lol.
I'm really tempted to create a video to help anyone else replace their ECU, i figured out a way to replace my ECU with a used ecu ($230) and program it for free, took me all about 30 minutes and the other writeup on this forum requires you buy a mazda dealer tool and have 2 keys. having an updated VIDEO on the process would probably help the community too (even though it's gonna be like 15 years late lol)
 
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Gabriel Buscema said:
I guess I did the oscilloscope test wrong because it was sending a pulse to my injectors on startup, and I couldn't test the injectors while the car was running due to the tmic lol.
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*Technically* you *could* have, though that involves having the TMIC off the car with the MAF completely unplugged. It's not really ideal and may run like shit but *should* be doable.
 
Gabriel Buscema said:
Alright guys, after 3 months of the car being down, injector cleaning and new seals not working, and not even the dealer figuring out what's wrong, I just fixed the issue
Turns out, it was the ECU the whole time!
I guess I did the oscilloscope test wrong because it was sending a pulse to my injectors on startup, and I couldn't test the injectors while the car was running due to the tmic lol.
I'm really tempted to create a video to help anyone else replace their ECU, i figured out a way to replace my ECU with a used ecu ($230) and program it for free, took me all about 30 minutes and the other writeup on this forum requires you buy a mazda dealer tool and have 2 keys. having an updated VIDEO on the process would probably help the community too (even though it's gonna be like 15 years late lol)
Click to expand...
glad you got it fixed. even if you don't make a video please make a write up.
around here I'd argue a write up is better as video links die over time messing videos the augments, same with any pics upload here directly so we don't lose them like we did with photo bucket
 
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