P0300 misfire quiet backfires

Just purchased 07 ms3 and I bought knowing it had some issues. First one was tb connector so replaced that then after I started car i got p0330 so I checked out the crankshaft sensor connector cleaned it and code went away until the p0116 popped up. After checking for open or short circuit with dmm when I put one lead onto terminal A of ckp and other lead on b+ and i am getting continuity. Oh terminal A is 12v referance. I chased it down to fuse box and get continuity all the way. Question is how do I go about fixing that.

 

2007 ms3 130k
Injen cai and turboxs bov and thats all for mods.
No tunes stock as far as i know
Bought the vehicle few months ago and first was throttlebody problems ended being throttle body connector was bad.
Then p0016 code so i replaced timing chain and all that except oil pump. Im new to turbos so I dont know if this one is performing the way its intended. When under load in first or second the turbo sounds like its drowning. Also stuttering and hesitating under load no codes are being thrown.

 

Which guide did you follow for swapping the timing chain. Did you swap vvt

Check your spark plugs gap make sure it's 0.027

 

2007 mazdaspeed 3
130k
Injen cold air intake that’s it for mods
Short history of what I know. I bought the car few months ago not running I diagnosed problem to be throttle body. Got the car to run and then p0016 code was popping up so I checked both crank and cam sensor and connectors. Was still getting code so replaced timing chain and vvt solenoid. After replacing all components for timing chain the first startup went as well as could be expected. No cel for first day but on the test drive I was noticing high pitched sound coming from turbo when I step on throttle along with stuttering loss of power. I have yet to drive this car when everything works as it should. Also this my first time with a turbo of any kind. I ordered a turbo so that should be here couple days. My issue is today I had to drive to appt and 3/4 of the way there the cel light came and I checked it out right and p0300 and from that point the engine seemed to misfire and make quiet backfire like sounds progressively worse until I pulled over and erased codes and from I made it home but light came back on few blocks after erasing but misifiring didnt seem to be bad or it was and I just couldn’t tell. Any input as to what could be wrong would be much appreciated

 

3 threads seemingly all related merged into one so people aren't split into 3 threads trying to help and can see the history easier.

 

Don't install the new turbo. Almost certainly not the problem

Check that you have everything in the intake tract connected properly after the vvt. Sounds like a messed up or broken connector to the tmic. Check the spark plugs gaps and report back

 

ok so I am still with the misfires. I have done a little bit work tryi g to find the soure of the problem. Since I last was here I have installed new seals on injectors orings and corksport seals.
I benchtested injectors cleaned reinstalled. Unfortunately I didnt listen about the turbo and got one from ebay for 120 installed and yeah same shit so I took the intak out and I got a fitting for ecbs vaccum line that goes to tintake jb welded it. New ngk 1x colder gapped at 28. Downpipe/racepipe I installed along with turbo. New map sensor. I just tested h02 sensor and 0.2-0.9 mv on signal wire.
With the work I have done the car now idles just fine with no cel. This car has been the biggest pos car I have ever owned in my life. I fix one thing and then right after another cel pops.and down again. Like I said now It idles like a good running csr and I can drive all.over town but like clockwork as soon as the rpms hit 3200 or more the cel starts blinkiING. Oh yeah acceleration is sluggish. The throttle is fine if drive like grammy. The power comes and goes real. Fast like and if I lightly press down I am able to feather it to get alot more speed and power. I hope this makes sense to you guys.

 

You don't need colder spark plugs install stock heat range

Do you have a hpfp upgrade

You need a tune and hpfp in order to safely run a downpipe

 

Ok and thats why when the motor is any kind of load higher than 3000 rpms the engine misifres because it needs more fuel. Its been doing this since before dp though. I will get other spark plugs.

Negative on the hpfp upgrade. I did take it to mazda dealer because they supposedly diagnose for free now but they diagnosed the misfire as exhaust leak the leak has been fixed and its still p03000. I dont know the proper way to check wire harness's and connector's so what I did is disconect the harness for coil packs and took a mm probed each wire for continuity also bending and pulling to see if connection could possibly be bad. The coil harness checked out so I am going to check out fuel injector harness next. I will install hpfp upgrade and let you know what the deal is. Much appreciate the help.

 

I figured out the po300 misfire under load. I was off two teeth on the ckp. I had only couple plastic bolts that I ordered off amazon for body/bumper work they came loose and the sensor slipped. I thought that getting rid of the p0300 would get rid of the sluggish/hesitation acceleration. It's still got no guts. I put in stock plugs from the ngk 1x colder. Car ran exactly the same with the stock plugs in. I ordered a upstream 02 sensor hopefully that takes care of the problem. Oh yeah I took it to a mazda dealer because they got a new special they are diagnosing cars for free. They said it might be your 02 sensor but I would need more time to further diagnose. Going off my scanners numbers the 02 sensor is fine. I'll find out monday.

 

Have you checked for boost leaks?

 

Did OP ever figure this out?