[SOLVED] Cyl 2 Misfire

JimmyFC

JimmyFC

Greenie N00B Member
Hey lads, currently chasing a pretty odd misfire on cylinder 2.
Just bought this bad Larry a month or so back, and was running fine until one morning went to start it up and got the P0302 misfire on the AP. Misfire doesn't appear immediately upon every start up, but only after a few seconds.
* AFR readings are consistent, not running lean even during misfire but STFT readings jump around -20/17 during normal city driving.
*Replaced plugs with 4 new NGK Iridium 6509's gapped to .028. Started up and misfire persisted. Swapped coil packs around and cylinder 2 is still misfiring.
*On WOT, fuel trims appear normal as does AFR readings, car does not misfire; only under low load and idle does the misfire rear its ugly head.
*Performed compression test & yielded following results:
1: 185
2:175
3:162
4:180

Currently in the engine bay to check out the injectors as this is my next guess.
Will update with logs when the pig is back together.
Any input is appreciated! Thx

Year/Make/Model: 2008 Mazdaspeed 3
Mileage: 162,xxx
DTC's: P0302
Modifications: Autotech HPFP
ECU/Tuning Software: Cobb Accesspport V3
 
What's ltft? At idle and cruise? Have you done a boost leak test.

Ideal parameters below
JohnnyTightlips said:
Pre-turbo = + trims, air added or sucked in
turbo to TP = - trims, air lost or pushed out
post TP = + trims, air added or sucked in

+5 or -5 is ideal
+7 or - 7 not crazy might want to look into it
+10 or -10 look into it , you got a leak
+20 or -20 shits broke yo
Click to expand...
 
Awafrican said:
What's ltft? At idle and cruise? Have you done a boost leak test.
Click to expand...
LTFT's are good, all the logs i took before taking the car apart were all under 4.

Though, i just got the intake manifold off and look at the valves from cyl 2 and i think this is my problem...

Looks like a bushing of some sort, no f'in clue how this guy got lost and ended up there. Wtf even is that?
 

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What the heck image format are you uploading in heic?
That's looks like the grommet from tmic or intake mounts. Wonder if it fucked your valves and piston...bore scope time

Reupload pics on this post so others can seeScreenshot_20240107-130443~2.png Screenshot_20240107-130543.png Screenshot_20240107-130532.png
 
Oops my bad haha, uploaded the pics from my MacBook. This was wedged bout halfway in, inspected the chamber there and it looks like it didn’t even make it more than halfway down.
 
Yikes!

Good thing you found that OP. As was mentioned I'd be looking to borescope and see what's going on.
 
It does look like the tmic grommet and luckily for you it looks like it stayed in one piece.

A horoscope is probably not a bad idea in case something else is in there. If it was my car I would check inside the cylinders then just bolt it back together and see what happens. Seems likely that something that large in the intake would mess up the flow in that cylinder.

I also wouldn't pay the 2x premium for a MacBook in order to surf the internet
 
Easter Bunny said:
It does look like the tmic grommet and luckily for you it looks like it stayed in one piece.

A horoscope is probably not a bad idea in case something else is in there. If it was my car I would check inside the cylinders then just bolt it back together and see what happens. Seems likely that something that large in the intake would mess up the flow in that cylinder.

I also wouldn't pay the 2x premium for a MacBook in order to surf the internet
Click to expand...
Horoscope huh? LOL
 
Thanks for all the helpful advice!
Definitely gonna go over the car this weekend with a fine tooth comb, see what other goodies i can find.
 
Well after an eventful weekend, all is right again.
Got a boroscope in and thankfully nothing is damaged. Valves are good as well as the piston head, looks like that grommet got lodged and held in tigh.
Took it for a few test drives and no misfire, engine back to normal operating conditions.
But of course it’s always something, and the boot for the slave cylinder has a minor leak but got an OEM replacement in the mail!
Thanks again for all the help :)
 
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