P0300 driving me insane

[Daniel Arteaga]

Hello, i had a 08 mazdaspeed 3 before but was not modded one bit, had to get rid of it. Settled for a CX-5, just to sell it and get another 07 Speed3 however this one was modded. Dumb of me to not actually take it on a long test drive because the next day on a cold start p0302 came up. I changed the plugs to LTR7IX-11 gapped at .026 and even swapped coils to a different cylinder just to see if it moves after but next morning on a cold start p0302 came back. I did a compression test and 180 on all four cylinders. I read some forums and suggested to inspect the injectors, removed them and sent them out to injectox to get cleaned and tested, they were fine, they also didn't appear to be leaking and they had the cs seals on them. Cleaned the valves while I was there. put everything back together and car was running fine. Next morning p0300 came on. it seems to only come on during cold starts, it never flashes and individual cylinders don't show on the accessport. With the light on the vehicle doesnt appear to drive bad or stumble on acceleration. i can clear the code and it wont come on until either the vehicle sits for long periods (more than 3 hours) or the following morning. i made sure everything that i had removed was plugged in. Im not too knowledgeable with these cars whenever they have mods on them so im learning as i go. Just looking for input to point me in the right direction to diagnose this car. i had posted on a different thread about what STFT and LTFT should be as to maybe that could be it? i attached logs sitting at idle or just cruising on my way to work. idk im at a loss right now, so any help would be greatly appreciated.
Mods: Stock reman k04, 2nd cat delete, cobb SF intake, Cobb Turbo inlet hose, cs hpfp internals, turbosmart bov recirc, cpe catless downpipe, egr delete.
Miles: 147000
Accessport V3
tuned by Freektune

 

[L337TurboZ]

It only happens on cold starts? Sounds like an injector to me. I don't know the firing strategy on Mazda DI engines but on GM engines we see cold start misfires with failed injectors due to the "dual pulse" they use when the engine is first started cold.

If the injector is leaking then it'll be noticable on cold starts and after 30 seconds to a minute it will smooth out.

You could swap injectors between cylinders to verify without sending them to be tested. Usually a P0300 is set initially until the misfire count on a specific cylinder reaches a certain amount which you'll then get a P030(X) code. You already swapped coils and put in plugs so I doubt it's that.

 

[Daniel Arteaga]

It only happens on cold starts? Sounds like an injector to me. I don't know the firing strategy on Mazda DI engines but on GM engines we see cold start misfires with failed injectors due to the "dual pulse" they use when the engine is first started cold.

If the injector is leaking then it'll be noticable on cold starts and after 30 seconds to a minute it will smooth out.

You could swap injectors between cylinders to verify without sending them to be tested. Usually a P0300 is set initially until the misfire count on a specific cylinder reaches a certain amount which you'll then get a P030(X) code. You already swapped coils and put in plugs so I doubt it's that.

I used to work at a Chevy service department, prior to me enlisting. So we would see any 5.3 with the injectors failing. But I did send them out to get tested, had an extra car so it didn’t bother me being down one. But they flow tested and cleaned and they were all good. That’s where I’m at a loss. Before I even did the work I would only get a p0302 no p0300 so that’s what threw me for a loop. I did order an injector but never put it on because they tested fine.

 

[L337TurboZ]

I used to work at a Chevy service department, prior to me enlisting. So we would see any 5.3 with the injectors failing. But I did send them out to get tested, had an extra car so it didn’t bother me being down one. But they flow tested and cleaned and they were all good. That’s where I’m at a loss. Before I even did the work I would only get a p0302 no p0300 so that’s what threw me for a loop. I did order an injector but never put it on because they tested fine.

It's a shame you can't use the AFIT on a Mazda. It also sucks that you can't exactly do a pressure drop test on the injectors with the AP. Do you have any other scan tool like a Snap On or even a copy of Forscan?

I have an MDI2 and was able to use it to communicate with the Mazdaspeed ECU's through Forscan. Maybe a test procedure could be located there. I haven't checked all what it can or can't do yet.

 

[Daniel Arteaga]

It's a shame you can't use the AFIT on a Mazda. It also sucks that you can't exactly do a pressure drop test on the injectors with the AP. Do you have any other scan tool like a Snap On or even a copy of Forscan?

I have an MDI2 and was able to use it to communicate with the Mazdaspeed ECU's through Forscan. Maybe a test procedure could be located there. I haven't checked all what it can or can't do yet.

I wish I had a snap on scanner lol. I did order a forscan should be here Thursday, just to see if it does or shows something the ap isnt

 

[StockishSpeed3]

Go check out my thread, I chased a P0300 just like you and since I’ve put my new flywheel and clutch on, no CEL. And I would clear my code and just like you, it would depend when it comes back on but usually first thing when your pulling out the driveway in the morning.

 

[Alden]

Hello, i had a 08 mazdaspeed 3 before but was not modded one bit, had to get rid of it. Settled for a CX-5, just to sell it and get another 07 Speed3 however this one was modded. Dumb of me to not actually take it on a long test drive because the next day on a cold start p0302 came up. I changed the plugs to LTR7IX-11 gapped at .026 and even swapped coils to a different cylinder just to see if it moves after but next morning on a cold start p0302 came back. I did a compression test and 180 on all four cylinders. I read some forums and suggested to inspect the injectors, removed them and sent them out to injectox to get cleaned and tested, they were fine, they also didn't appear to be leaking and they had the cs seals on them. Cleaned the valves while I was there. put everything back together and car was running fine. Next morning p0300 came on. it seems to only come on during cold starts, it never flashes and individual cylinders don't show on the accessport. With the light on the vehicle doesnt appear to drive bad or stumble on acceleration. i can clear the code and it wont come on until either the vehicle sits for long periods (more than 3 hours) or the following morning. i made sure everything that i had removed was plugged in. Im not too knowledgeable with these cars whenever they have mods on them so im learning as i go. Just looking for input to point me in the right direction to diagnose this car. i had posted on a different thread about what STFT and LTFT should be as to maybe that could be it? i attached logs sitting at idle or just cruising on my way to work. idk im at a loss right now, so any help would be greatly appreciated.
Mods: Stock reman k04, 2nd cat delete, cobb SF intake, Cobb Turbo inlet hose, cs hpfp internals, turbosmart bov recirc, cpe catless downpipe, egr delete.
Miles: 147000
Accessport V3
tuned by Freektune

I have the exact same issue, and also tried pretty much exactly the same stuff you did. Does yours sound pretty rough on cold start? like RPMs dipping and bouncing back up, similar to a VTCS delete? At this point, i just slightly depress the gas pedal on start up to override the cold start.