Bucking underload and moving misfire

[Awafrican]

I don't see one, also I think it's time for a compression test. Skimmed through thread again didnt see one posted (could have missed it)

 

[2008ms3nick]

Not yet but what logs do you need I can do readings on my scanner in a moment

These are all the stats I can get you guys at the moment my scanners not the best
(Cold start)

I did a compression test 3 months ago and I tested 175,175,175,160

 

[jsmith]

You dont have an Access Port? Does the Cobb SRI require a MAF cal?

Does your intake look like this one?

https://www.cobbtuning.com/products/mazdaspeed3-sf-intake-system-mazdaspeed3-2007-2013

 

[2008ms3nick]

I have the corksport sri and it looks like it does have a plastic inner housing around the mass air flow sensor, this one to be exact

https://www.google.com/amp/s/corksport.com/amp/mazdaspeed-3-short-ram-intake.html

 

[jsmith]

I only have a cobb Sri installed.

Just quoting what you had said initially and below from the Cobb site.

"All aftermarket intakes for MAZDASPEEDs require tuning in order to ensure the MAF sensor reads properly and the engine operates within safe parameters."

Edit. So what that means is if you dont have an Accessport (a way to tune to ensure the MAF sensor reads properly), that the lack of one may be your issue.

 

[2008ms3nick]

Oh , I was told by Zach at corksport that the Sri can be installed and run without a tune, I’ve had it on there for about a year now and with or without it my car is still bucking at wide open throttle with a changing misfire, at first a year ago it was cylinder three that gave me the most issue so I swapped out the injectors and coils and it seemed to be fine for a week and then it went to cylinder number one and now cylinder number 4 with a random misfire only on WOT. But now she just won’t run without idling right which began about a day before I started this thread, I just cannot figure out this car

 

[jsmith]

So you don't have an access port, OK.

Can we get some pictures of the engine bay and complete, as you know it, mod list?

 

[2008ms3nick]

Mod list -
Corksport Sri
Rear resonator delete

edit- this is how she is currently running

 

[2008ms3nick]

Update- took it to the dealer and they did a internal diagnostic on my cylinder head and found a burnt exhaust valve on cylinder 4, so I’m looking at a pretty hefty fix.


Anyone got any heads laying around they are trying to get rid of? Will pay if the price is right

 

[Easter Bunny]

For what it's worth Cobb is the only Sri that won't run correctly on stock tune. All of the other stockish size ones including corksport will be fine

 

[originalmarshmello]

You can check the pressure relief valve by monitoring HPFP pressure after a hot shutdown. If your fuel pressure (which should be at ~1000 PSIish) starts dropping after you shut the engine off...its likely the relief valve failed/failing.

The relief valve is on the driver side by where the water exits the block. See picture below, look for the yellow clip thing I am pointing at.

View attachment 15771

I am having a similar gremlin appearing at wot, and was planning to test this relief valve on my AP. How much drop in pressure after shutting off is acceptable? None?

My car seems to run, albeit +15 on the fuel trims, without obvious misfire at low to even moderate engine load, but on wot it bucks. Started happening on the final revision my tuner was doing. The car went strong for the whole session but the last revision he did made it wonky. It was not lean before it started bucking. I have new coils, new NGK 1 step colder plugs (0.026” gap, no visible damage), so I’m assuming neither of those would be the culprit. I also had cleaned my injectors, resealed them, they passed the flow test flawlessly.

mods are:
Htp 3.5 intake
TurboXS DP and Race pipe
Cobb catback exhaust
Autotech hpfp internals
ETS TMIC
BNRS4 turbo

Thanks in advance!

 

[Easter Bunny]

when testing the PRV the fuel pressure should climb to 1600 then release any pressure less than that is a failed valve. just make sure the car is hot when you do the test

 

[Awafrican]

+/-15 on ltft you have a leak somewhere... and need to find it yes the car will run but as you can see not always well

 

[originalmarshmello]

Turns out my issue was with an ignition coil. I had just replaced the oem ones (causing spark blowout) with brand new densos from rock auto. One of those failed, I got it warrantied, and now seems to be working fine.

 

[Awafrican]

glad you got it sorted