p0300 only when under boost

2007 mazdaspeed 3
130,000 miles
Cai, cheap-o dp/racepipe
Corksport tb
Tuneless
P0300 still fighting changed spark plg twice maf, map, ckp, cmp, new turbo, timing chain and vvt stuff and 02sensor, injector seals cleaned, battery, changed oil several times and motor mounts.

I just did a compression test 10 minutes ago 160psi all 4 cylinders. Spark test comes back good. Boost leak test passed.

Still fighting the p0300 stutter under load which anytime i punch it used to go into limp mode now the cel blinks amd throttle still pressed but the speed comes and goes and I can drive lkke granny forever but its like as soon as I give enoufj throttle for the turbo to start car stutters and cel blink. The only test I havent done is leak down but I was under the impression that if engine has compression in all cylinders there is no need for a leak down test.

THere seems to be a good amount of people kinda the same issues but 95% of posts I read on this problem nobody ever solves or they arent sharing.

Oh yeah I even tried replacing the ecu with pos company flagship -0.

 

Have you considered getting a tune? CAI & DP. What size intake? Do you have HPFP internals?
Even my CEL-less skinny Corksport Stage II CAI & TIP work better with a tune.

 

I'm with Synthetic here you need a tune and HPFP internals if you don't have them at a minimum. I'm assuming you have no way to data log since you don't have a tune. I'd be very curious to see what your fuel pressure looks like at WOT.

Also about your assumption with the good compression test and not needing a leak down well that's not the case. My OEM motor had good compression numbers but terrible leak down right before I went built motor.

 

Need a tune and hpfp

 

OP you're lucky you still have good compression, as easter bunny said you need hpfp internals (this should have been done before adding an intake let alone DP) and a tune.
Go with freektune or purple drank, even if you just get the ots+ map from freektune. If you don't already have an access port then if you buy it from freektune he gives you an ots+ map for free, essentially it's a MAF cal + 1 revision after for your car. If you don't want cels at all then you've got to go versatune as Cobb doesn't let you disable them anymore (blame California)

 

So a pcm thats bad or going bad couldnt cause these issues. Only #2#3 misfire counts. I pulled the spark plugs for tests and the two that have all the bs going on they are clean no soot ot anything. Middle 2 are misifres. Looks like they been washed to me. What do yall think?

 

downpipe and no HPFP=bad time

 

The flashing CEL happens during a missfire event. It stops when the missfire event ends. That what it means.
Compression test tells you how well the cylinders can compress air, Leakdown tells you how much of that compression stays in the cylinders and helps you distinguish where it might be going if the loss rate is bad.
If you have a CAI and no tune, your computer is making computations for air/fuel mixture that are flawed as the MAF isnt calibrated for the flow characteristics of the pipe it is located in. A tune is required to remedy this. This could be the reason for your missfire.
Your downpipe isnt the same as the stock unit. Flow characteristics arent the same, and the change in backpressure will mess with the computers ability to make proper computations again for air/fuel mixture. A tune is required to remedy this. This could be the reason for your missfire.
You dont mention having HPFP internals. This is in my view the 1st upgrade any Speed needs. You dont want a fuel pump that cant keep up at WOT.
Yes the lack of tune for your CAI & DP, as well as the lack of HPFP internals *might* not be the reason for your issues, but you are playing poker against almost 20 years of blown Speed engines due to owners making these mistakes.
Not having a means to log parameters is like diagnosing in the dark. Kinda like trying to diagnose a CEL without a code scanner.

 

Wait are you running the corksport throttle body with no tune?

 

You don't need one with this. I didn't retune. However when I did it smoothed acceleration out a lot.

 

Today I learned

 

"Don't need" as you've pointed out it's better when tuned for it, also CS recommends a tune for engine health;
"The CorkSport Throttle Body can be installed with no tuning, however, to ensure optimum performance and engine health, a tune after installation is recommended"
https://www.google.com/amp/s/corksp...e-throttle-body-for-2006-2013-mazdaspeed.html

I certainly wouldn't run one in my car without a tune, but I'm one dude on the Internet

 

More than one feel that way!

 

Oh I know. It definitely was smoother with the tune touched up

 

Raider, I ran my Speed with a CorkSport stage 2 intake and no HPFP on the OEM tune for 140,000 miles with "no issues" before I knew better. I wouldn't do it again but nothing seemed out of the ordinary.

 

Gen1 you can do pretty much everything but catless dp w/o a tune. I did for a long time too.

 

When I bought the tb corksport said it.would be fine without tune. Anyways I bought mbership to versatune light and was.going to install last.night but all the tunes are either 91 or 93 octane and where i live i cannot find 93 only 92 and 89. Can I run tune that calls 93 on 92 or?

 

just run the 91 tune on 92

 

I didnt get a response fast enough so i first went with the first tune and still misifre. Super bummed but then I changed the tune to a differnt and for the first time in 6 months I am able to drive however with no cel blinking in my face..fuck yeah the help much appreciated. Shoulda listened the first.post. but I hard headed like that. Thanks again to yall.