P0300 code random multiple cylinder misfires after mods

[dennisdiecast]

Ok so here is my story. Over the winter i installed Van's 13-6 kit with the lower 10% ATI pulley and i installed stainless work headers with off-road H-pipe. When i drive the car and go over 4500rpm i get the P0300 code (even if i'm not going into boost and slowly increasing rpm in 2nd gear). Did a data log for Lund and the tune was all good according to the logs.

I contacted Van and he suggested that there is a possible vacuum leak and/or i need to do a crank re-learn. So i took the car to BPS and they performed a smoke test and found no leaks, they also changed the spark plugs to the TR06 and gapped them at 0.028, the sct programmer wasn't able to do the crank re-learn so they installed the original air intake and put back the original tune so i can take the car to Ford. Ford was able to do the crank re-learn. So i came home and re-installed the JLT air intake and the throttle body and re-tuned the car. Took the car for a spin and still at around 4500-5000rpm i get the P0300 code.

Spoke to the guys at BPS and they said to put the original tune and install the original air intake and try it again. Slowly going up to 4500-5000rpm i get the same code again. The only thing non-original on the car at this point is the 10% lower pulley, the headers, and the spark plugs.

Anyone care to chime in on some possible solutions?

 

[SCGallo2]

Attempt to duplicate the problem again and monitor your AFR between 4500-5000 rpm to see if it goes lean. Did any of your O2 sensors get damaged when swapping them to your new headers and O/R pipe? Maybe recheck your O2 sensor electrical connections.

 

[Snoopy49]

From the 2014 Mustang Service Manual

View attachment P0300 - Random Misfire Detected.pdf

 

[2011 gtcs]

You didn't put 02 sensor extenders on did you ? I know that messes with the car. Other than there being a issue with the crank pulley I'm not sure what else it could be.

 

[Shelbanator]

I had the same code pop up on me aswell about a week ago what i did was change my spark plugs i noticed the plugs i had installed (auto lite) when i had my pulley swap done werent cool enough and figured hell this is a brand new car theres noway it can have a cylinder misfire already so as i went to remove them all 7 came out perfect except for 1 wich i assumed was the bad one and i threw on some tr7ix plugs and ever since then problem solved

 

[railroad]

You have a PM

 

[Lillou74]

My car started the same thing last weekend. My tuner says I have a air leak, I'm yet to find it. I data logged and he adjusted my tune so I have no KR. I noticed my left exhaust tip is black and right is fairly clean. Ive checked plugs twice and they all look good. I'm thinking possibly fouled plugs. I also ran Torco for the first time last weekend. I just got motocraft sp-471 spark plugs and I'll be installing them tomorrow. Keep us posted and I'll reply on my results. Thanks

 

[dennisdiecast]

Attempt to duplicate the problem again and monitor your AFR between 4500-5000 rpm to see if it goes lean. Did any of your O2 sensors get damaged when swapping them to your new headers and O/R pipe? Maybe recheck your O2 sensor electrical connections.

yes i'll have to check that, what should the AFR be at? i'm pretty sure the O2 sensors are ok, i was very careful with them... but that could be an issue and i will recheck the connections. Also i did not put the O2 extentions on since Van told me they aren't good for the car.

I had the same code pop up on me aswell about a week ago what i did was change my spark plugs i noticed the plugs i had installed (auto lite) when i had my pulley swap done werent cool enough and figured hell this is a brand new car theres noway it can have a cylinder misfire already so as i went to remove them all 7 came out perfect except for 1 wich i assumed was the bad one and i threw on some tr7ix plugs and ever since then problem solved

I had the TR8IX that came with the kit and even with those plugs i got the error code. I just find it weird that the car runs perfectly (even when going into boost) and then when it reaches 4500-5000rpm it throws the codes. Even above 5k rpm i don't feel any hesitation with the car or anything.

 

[SCGallo2]

yes i'll have to check that, what should the AFR be at?

Just easing into the gas pedal (not going in to boost), I would expect to see less than 15. 16-17 is leaning out and you should feel the car stumble with a momentary reading above 17. Under boost at WOT, I would expect to see 11.1 to no more than 12. These values are derived from datalogging my own car while drive tuning.

 

[Lillou74]

Has anyone resolved this issue?
I have changed plugs, checked coil packs, smoke test for vacuum leak. No progress, wondering if it has something to do with EGR valve sticking.
Any help would be appreciated. Thanks

 

[Ghoust]

I got this code today as well. I just came home and parked the car..I haven't gotten a chance to mess with it yet. I am curious as to what your guys' diagnosis was?

 

[Lillou74]

I have tried everything that I could think of and nothing has changed. I just put all the original parts on and it will be going to the dealership. I'll let ya know what I find out.

 

[dennisdiecast]

I have tried everything that I could think of and nothing has changed. I just put all the original parts on and it will be going to the dealership. I'll let ya know what I find out.

are you still getting the code with all the original parts back on? (when i put back the stock tune, throttle body and intake i still got the code). Playing around with the car on friday i found that my crank bolt had come loose, so i'm really hoping that is my problem, gonna be taking the car to BPS on saturday for them to pull the crank pulley and inspect the crank snout and they're gonna install the ARP bolt, (also gonna have them check that the header install i did is ok). Hopefully this will solve my problem.

 

[Lillou74]

I haven't drove it yet but it still has a slight miss at idle. I've been so frustrated, I've worked on the car every free min this last week. I had upper pulley so I doubt it's my crank bolt but you never know. I'll drive it tomorrow and post what it's doing. Thanks