P0300 code only at high rpm's under load

TheGreatWhite5.0

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So when I'm driving my car, when I go WOT and over 6500 rpm's my car starts to flash the check engine light and its a p0300 code. I check my misfire data through a handheld I have and I have misfires on every cylinder as follows (cylinder and number of misfires): cyl1-8 cyl2-2 cyl3-18 cyl4-1 cyl5-4 cyl6-7 cyl7-7cyl8-1. This problem started occuring randomly so I'm not sure what caused it.
My car is 2014 Mustang GT block
10.45:1 compression ratio
Fully built (manley rods/pistons/arp-bolts/billet oil-pump-gears)
Automatic
Roush 2.3 blower, 79mm pulley, jlt 123mm maf intake, ported elbow, stock kit gt500 tb, Deatchworks 95ib injectors, and I have a Boost-a-pump.
I run cali 91 octane and sometimes use VP octanium booster, not sure if that would have anything to do with it
car is Lund tuned and I've asked Jon jr. to look through it and he says its a 'lean misfire' and leaning out at the top. He thinks its the injectors but what are the odds 8 injectors are failing? I've changed the spark plugs, done a crank relearn, kam reset, and swapped coils around and it still is happening.
 

MastaAce03

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That's not good man, don't get on it anymore until you figure this out.

What's you're FPDC at? Also, make sure you're running the correct heat range spark plugs for your setup.

Vp Octanium is some good stuff, are you sure you're using enough of it to deter detonation?


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TheGreatWhite5.0

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What is FPDC? I'm running 2 step colder NGK plugs and gapped at .028 The car was running great and everything was good. Took a trip to vegas, came back, few days later was doing some pulls and everything was great. Few days later was doing some more pulls and it started to have the issue.
 

MastaAce03

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What is FPDC? I'm running 2 step colder NGK plugs and gapped at .028 The car was running great and everything was good. Took a trip to vegas, came back, few days later was doing some pulls and everything was great. Few days later was doing some more pulls and it started to have the issue.

Sorry, fuel pump duty cycle.


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MastaAce03

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You have to data log to figure out the FPDC. Have you data logged your car at all after the new motor and tune?


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TheGreatWhite5.0

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Yes I have multiple datalogs that I sent to Lund Racing, Jon jr. said its a lean misfire and thinks its the injectors. I've checked to make sure they are seated and everything seems to be working fine. If they weren't seated correctly I'd think it would be showing more of an issue at any rpm, not just at 6500 plus, and I'm doubtful that all 8 injectors would be bad causing all 8 cylinders to have misfires.
 

basspro302

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Sounds like a weak fuel pump. I would hook up a fuel pressure gauge or drop pulley sizes to lower the boost see if that helps. You might be running out of fuel up top
 

nxhappy

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Faulty spark plug (s) ,Faulty ignition coil (s) ,Clogged or faulty fuel injector (s) ,Intake air leak ,Fuel injectors harness is open or shorted ,Fuel Injectors circuit poor electrical connection ,Ignition coils harness is open or shorted Ignition coils circuit poor electrical connection Insufficient cylinders compression Incorrect fuel pressure

first simple check air intake leaks or vac leaks
could be partially clogged injector, run some lucas injector cleaner through it
put a gauge on it, measure fuel pressure
do not run it WOT anymore, it's running lean. You WILL cause damage.
 

TheGreatWhite5.0

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Update, so I re-checked everything. Plugs are all good, had a shop look at everything and they say it all checks out. Put it on the dyno and Air/fuel all looks great. I did some data logging and ran through the logs, short trims on bank 1 and 2 look decent. At WOT 6900rpm, bank 1 is at .99 and bank 2 is at 1.02 about. I cant see this being my issue. Car now has Kooks 1 7/8 headers and high-flow cats as well. Another thing, maybe its just because they didn't run the car to 7k on the dyno but those numbers seem very low for what I have :/ Dynojet
 

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twistedneck

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I have the same issues - cant get the P0300 to stop turning on... for years now. I investigated the hell out of it with no luck everything from clutch re-sets to new crank trigger sensors and wheels. and plugs and intakes and the biggest fix was two new cheap ass bosch O2 sensors. best money I've spent. h

had no clue the e85 was eating them up and making my car slow.

I also swapped out injectors because the e85 turned them into stick sludge due to a blow by issue I had with wrong oil.

anyhow - I think we need a new ECU to fix that and if I go that route its AEM time with one of those cool mini dash boards and 9600 RPM capability!!
 

TheGreatWhite5.0

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Update:
I fixed the issue with headers lol for some reason after doing a header install the code went away and never came up again. Exhaust leak somewhere maybe was causing it and when putting in the new exhaust everything was re-tightened and buttoned up. 02 sensors were a little lose as well so my guess is it was something to do with that.
 

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