P0300 Random/multiple misfire

[bananabread]

Hello, I’m dealing with a p0300 and
p0301-308, misfire on all 8. Car is a 2017 gt, 6r80, 2018 manifold locked out, free flowing exhaust, Paxton 3.6 pulley on 93 with boostane lund tuned. Filled up with 93 and boostane and drove the car for half a tank over two days, parked it for 2-3 days and changed the belt and it started misfiring after that. Car starts fine and idles fine but you can hear the misfires from the small exhaust pops but won’t throw a code. Idle rev and hold 1-2k and she’ll throw p0300-p0308 after a few seconds. Drives fine and pulls hard. She’s on a clean tank of 93 now, new spark plugs, new o2s, crank relearn, smoke test for vacuum leaks, compression tested, leak down test, and everything looks great. Any advice, tips or ideas of what it could be, or how I should go about figuring this out? Thanks!

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[Cobra Jet]

A random code like the P0300 is a PIA and no one on here would be able to give you a definitive "it's this part".

However, here's some things you can check:

Check the connector at the MAF and make sure it's totally secured. Make sure you don't have any breaches along the air intake track, or any cracks damages to the intake. Any such breach before or after the MAF is a vacuum issue and will skew signals for incoming air flow monitoring.

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Pull the plugs and post images of what you find for their readings/condition.

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- VCT solenoids - if the solenoids are not operating properly due to debris or they are failing due to age, they can cause such codes. Quite a few threads on here about these prematurely failing and/or how to diagnose.

The culprit here was the VCT solenoid::
https://www.mustang6g.com/forums/th...s-and-cam-retarded-codes.176734/#post-3571964

Here's (2) more threads for VCT info that I had previously posted in other threads:
https://www.mustang6g.com/forums/threads/2015-2021-s550-5-0’s-ssm-50067-vct’s-again-various-dtc-codes.169419/

https://www.mustang6g.com/forums/threads/p0018-code.123932/

- Crank sensor - failure can be the sensor itself, the harness to it or the pins in the connector. If the crank sensor is failing, it also will throw various misfire DTCs. The only time the crank sensor will throw a specific crank DTC is if the sensor is disconnected or it has completely failed. Many have found even with a generic misfire P0300, that the issue was related to the crank sensor. These sensors do not last forever due to their location and under hood heat cycles.
Check this thread:
https://www.mustang6g.com/forums/threads/misfire-at-high-rpm.174380/#post-3531453

AND this one:
https://www.mustang6g.com/forums/th...e-sensor-tone-ring.156234/page-2#post-3197692

The IMRC design has been problematic since the IMRC intake system first debuted in the 1994 Lincoln MKVIII with the 4.6 DOHC (which was then carried into the 1996 Cobra and beyond). Theres MANY threads on here regarding the intake and IMRC system.
https://www.mustang6g.com/forums/threads/possibly-broken-imrc-shaft.183221/#post-3689879

Hope something above was helpful.

 

[KingKona]

It's a cracked intake manifold.

This is extremely common, and always produces those two codes.

 

[bananabread]

It's a cracked intake manifold.

This is extremely common, and always produces those two codes.

Is this common? I smoked the manifold but didn’t see any smoke, out of ideas now. At this point injectors we’re cleaned and tested, new crank sensor and relearn, new maf, oem fuel pump. I even pulled the motor and took the heads off and looked over everything and nothing looked off. New vct solenoids and phasers and all new timing and still misfiring at idle and really starts misfiring at 1500rpm and goes away any higher. Throws p0300 and will eventually throw 301-308 after I hold 1500rpm, no cylinder misfire stands out more than the others.

 

[bananabread]

Here are some images after removing the head, car was over diluted with boostane over maybe 2 weeks
54k miles

 

[17MagMetal]

Here are some images after removing the head, car was over diluted with boostane over maybe 2 weeks
54k miles

Boostane caused all that surface rust?!?

Was there any coolant residue in/near the cylinders? A “simple” answer here might be boost pissed off the headgasket. Minimal, minimal coolant got into the combustion chambers and wam bam misfire codes.

 

[17MagMetal]

Is this common? I smoked the manifold but didn’t see any smoke, out of ideas now. At this point injectors we’re cleaned and tested, new crank sensor and relearn, new maf, oem fuel pump. I even pulled the motor and took the heads off and looked over everything and nothing looked off. New vct solenoids and phasers and all new timing and still misfiring at idle and really starts misfiring at 1500rpm and goes away any higher. Throws p0300 and will eventually throw 301-308 after I hold 1500rpm, no cylinder misfire stands out more than the others.

For clarity: If they meant the IMRC rod crack in the intake manifold, it should be a nonissue for you. You’ve been locked out/tuned/boosted.

I’m not sure if the FI guys have actually broken intake manifolds before though.

 

[bananabread]

Boostane caused all that surface rust?!?

Was there any coolant residue in/near the cylinders? A “simple” answer here might be boost pissed off the headgasket. Minimal, minimal coolant got into the combustion chambers and wam bam misfire codes.

The head gasket seemed fine, the car was never overheated and never smoked from exhaust. Coolant levels never dropped either. The orange coat is the lead or whatever from the octane booster being burned, it all wiped off clean with fuel system cleaner. There was a lot of it though from it being over diluted in the tank

 

[17MagMetal]

The head gasket seemed fine, the car was never overheated and never smoked from exhaust. Coolant levels never dropped either. The orange coat is the lead or whatever from the octane booster being burned, it all wiped off clean with fuel system cleaner. There was a lot of it though from it being over diluted in the tank

Awesome, glad it’s not/doesn’t seem to be that. I honestly can’t offer much more than that. A tuner that can pull/read live data might be able to help you out with the misfire. Hopefully it’s all ignition related.

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