p0300 and 6 other cylinder misfires

[Rypkr937]

2015 gt all stock. 24k miles. A few weeks ago I had my AC compressor fail. Got it back and probably 200 miles later I got a check engine light.

Autozone printout says p0300 random cylinder misfire as well as 6 of the other 8 specific cylinder misfires. I had just put a few gallons of gas in it probably 20 miles before this happened. Drove around to burn it down and then refuled with new 93 and code went away. 2 days later the on my way to work this morning I got a flashing check engine light. I haven't pulled the codes yet. In neither instance did I feel any misfiring or sluggishness or anything abnormal.

I'm aware of the IMRC issue on these intake manifolds but if that were my issue wouldn't it only be cylinders on one side? I have at least 6 cylinders throwing codes. Could this somehow be related to something with the new AC compressor or something during the install? The autozone printout references doing a PCM reprogram alongside the p0300 code - is that a practical viability? I tried disconnecting the battery for a few hours but that didn't discharge the system. Will resetting the keep alive charge possibly help? How is that done? I'm really not trying to take this to the dealer out of warranty and have them troubleshoot everything under the sun.

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[Rypkr937]

Anybody????

The question I REALLY need answered is if the IMRC failure would cause misfires on both sides? So far I've logged individual misfires on every cylinder but 1 and 8. Im trying to figure out if I should start there to troubleshoot this but my rudimentary understanding of the intake I'd only be seeing misfires on one side of the engine unless both sides broke.

 

[nnnnnn]

I currently have misfires. Sometimes I get P0300 and sometimes it's just one cylinder alone but most of the time it is on cylinder #5. Initially I got the p0300 AND I've been fighting it for a while and I have a 2016 mustang. But let me update you so far on what has been checked:

initially I had a P0301, I didn't immediately take it to a shop and then it evolved to a p0300, then a P0305 too but upon towing it to a shop about 4 weeks ago, it was a dead coil on #5 and I think a dead plug too. They replaced all my spark plugs and replaced #5 coil. The other coils were fine. They also replaced all spark plug boots. I had a reische 170 thermostat installed that time as part of all that work.

The code was cleared, I started driving it. I go to start it and it just starts flashing check engine and idling rough, then it went away. I took it back, they suspected a bad fuel injector but then after taking it back, they checked and they saw the fuel injectors were fine. I asked them about the throttle body and they said they checked that too.

A compression test was done and it passed compression. The shop manager though who used to be a ford service dealership manager for many years said that although it passed his alternative compression it showed a 3% power loss which he couldn't figure out why. The code was cleared and when I drive, as long as I don't hit high rpm, it ran fine. Once I hit 5k rpm, it came on. He recommended I take it to the dealership.

So I did. I took it to the dealership, they wanted to open the manifold and check the imrc shafts to see if they were cracked. The fee to open it and check is $1k on top of diagnosis fee. I said no way, I want my car back. This is just to check not to fix the problem. Since imrc were part of manifold and with FI, manifold gets replaced I said, I'll do my SC install. The fuel injectors were checked at the dealership, spark plugs, coils, no issues. For you maybe have those things checked too. The other thing will be the manifold and imrc shafts. Took it to my SC installer and SC was installed. A roush.

I have added a Roush Stage 2 since then and then misfire came on quick. The installer asked how long I had been fighting that cylinder misfire and I told him a few weeks. Before I left, he swapped out my crank position sensor with a used one and then misfire only came on at a higher rpm. The misfire would come at high rpm, engine would flash and sometimes it would go away on its own. He recommended I change both the camshaft sensors and crankshaft sensor together and report back. I still have cooling mods to do with them and if I still had issues, it will be further looked into by them.

This coming monday, I am having all four camshaft sensors replaced per the SC installer recommendations. He also recommended replacing the crankshaft position sensor. I will also have them put new ignition coils on the remaining 7 cylinders just to change them out. I hope my post has been helpful to you. And by Tuesday next week, hopefully that fixes the issue.

Right now I still occasionally get the P0300 even though #5 is causing the issues mainly.

 

[nnnnnn]

Update for you: I had 2 intake camshaft sensors replaced, 2 exhaust camshaft sensors replaced as well as my crankshaft position sensor and pigtail for it replaced and that still did not fix the high rpm misfire issue. The mechanic said that the car runs too good to have any issues and it must be something in the programming.

I was told I had the wrong ignition coils but I need to follow up on that so coils weren't changed.

So misfire at high rpm still exists for me. Maybe at least you know what to check for based on my troubles so far. Definitely have your intake taken out and your IMRC Shafts examined to see if they are cracked or something.

My next plan is to have all my ignition coils replaced and maybe new MAF sensor? My Roush Phase 2 SC already comes with a new MAF assembly so maybe existing sensor is bad. who knows

 

[SensesFail]

I had the same issue on my '16 GT. I ended up locking out the IMRC and tuning out the DTCs with Palm Beach Dyno. Do you guys feel these misfires when they happen? I would have never known if I didn't look into $6 with OBDWiz on my laptop. I thought misfires were extremely noticeable not subtle.

 

[nnnnnn]

I had the same issue on my '16 GT. I ended up locking out the IMRC and tuning out the DTCs with Palm Beach Dyno. Do you guys feel these misfires when they happen? I would have never known if I didn't look into $6 with OBDWiz on my laptop. I thought misfires were extremely noticeable not subtle.

For me they're not noticeable at high RPM. But sometimes at initial start if it randomly misfires, it idles rough but that's random and on rare occasions. I wonder what OP has done since. OP have you had anything done so far?

 

[SensesFail]

For me they're not noticeable at high RPM. But sometimes at initial start if it randomly misfires, it idles rough but that's random and on rare occasions. I wonder what OP has done since. OP have you had anything done so far?

Define rough idle; RPM fluctuating?

 

[nnnnnn]

Define rough idle; RPM fluctuating?

No the RPM doesn't fluctuate. The whole car body shakes a bit, check engine light comes on quick, starts flashing immediately. I turn the car off, wait like 15 seconds, turn it back on and no more flashing check engine and rough idle and it drives smooth. That random start misfire happens out of nowhere. The only thing I now want to rule out is ignition coils. Going to have all replaced. My mechanic told me #4 ignition coil was replaced not #5 and he said they could swap the coils to test it. I haven't taken him up on that offer yet since I'd rather just replace the remaining 7. I'm having CarId work one exchanging my standard coils UF824 coils for motorcraft coils since the standard ones don't fit per mechanic. They're pretty easy to do but I'd rather not mess with it and have professional do it.

Just sent an email to my roush installer shop asking if the IMRCs were locked out in the tune. I'm pretty sure roush SC replaces the upper and lower intake manifolds completely so if it was the imrc, that would have been swapped out correct? And I don't know if OP has had a manifold replacement done

 

[nnnnnn]

Replaced my MAF Sensor too, that wasn't the problem but car ran better litte as far as throttle response but that specific cylinder misfire is there. If I cold start the engine and leave it for 2 min, it just starts to idle rough, throws misfire code, CEL later starts flashing etc but if I start it and get moving as soon as I start, none of that happens and the light hasn't come on for some weeks now until I leave it long on idle after starting. Now, all is left is to replace ignition coils, spark plug wires, purge valve and purge reservoir which I'm waiting on.

If all that fails, the only thing I can think of is broken valve springs but I'm not jumping to that conclusion yet due to the fact that it passed compression when it was checked.

 

[nnnnnn]

Today I received a new Purge Canister Valve also called EVAP Purge Valve. I replaced the current in it as soon as it was delivered. I took it for a test drive, hit 5k rpm and check engine light did not come on. I only got a chance to hit 5k rpm once. Car idles better too but it's all too early to know. But so far I hope I have fixed the problem.

I haven't replaced ignition coils yet, parts on hand. I'm also expecting a vapor canister reservoir. I still plan on replacing ignition coils either way but so far car runs better.

 

[Temovic55]

Interesting! I never had those codes when the car was bone stock but once I installed my Odin kit it stated to give P0300, P0304, P0306 on several occasions. Along with some fueling issues, P0175, P0172 BUT I have changed my tuner and still waiting for the new tune to be sent and then I could be %100 sure the car has no mechanical failure! Only unfortunate Ex-tune!

 

[nnnnnn]

Interesting! I never had those codes when the car was bone stock but once I installed my Odin kit it stated to give P0300, P0304, P0306 on several occasions. Along with some fueling issues, P0175, P0172 BUT I have changed my tuner and still waiting for the new tune to be sent and then I could be %100 sure the car has no mechanical failure! Only unfortunate Ex-tune!

Have you had a compression check done?

Mine has gone through compression check as of this weekend, came out fine so I know it's not the block. I thought I had fixed the issue but it's still somewhat there. The CEL comes on flashes then disappears. Ignition coils were replaced this past week and also charcoal canister.

Looking forward to knowing what they find on yours. For me, my next step will be engine wiring harness replacement, or VCT Solenoid but not anytime soon. I'm fed up of this gremlin. it's already put me through needless costs and various people can't seem to find the problem

 

[Temovic55]

Have you had a compression check done?

Mine has gone through compression check as of this weekend, came out fine so I know it's not the block. I thought I had fixed the issue but it's still somewhat there. The CEL comes on flashes then disappears. Ignition coils were replaced this past week and also charcoal canister.

Looking forward to knowing what they find on yours. For me, my next step will be engine wiring harness replacement, or VCT Solenoid but not anytime soon. I'm fed up of this gremlin. it's already put me through needless costs and various people can't seem to find the problem

Mine running waaay better now! no codes or whatsoever after the new revision tune. The surging is not noticeable between gears or even while stationary so I think mine was having bad tune at the beginning.
About your car, how many miles ? forced induction ? tuned ? aftermarket front grille ? if not, I would check VCT Solenoid or at least flush them then install them back for testing. If the car did pass the Compression test then coils, sparks..etc are fine.
the misfire is pain tho..really can't point out a single suspect!

 

[nnnnnn]

Mine running waaay better now! no codes or whatsoever after the new revision tune. The surging is not noticeable between gears or even while stationary so I think mine was having bad tune at the beginning.
About your car, how many miles ? forced induction ? tuned ? aftermarket front grille ? if not, I would check VCT Solenoid or at least flush them then install them back for testing. If the car did pass the Compression test then coils, sparks..etc are fine.
the misfire is pain tho..really can't point out a single suspect!

I have 86k miles, it's got FI but the issues started before FI install. The front grill is aftermarket but it's been on it for like over 40k miles before I had this issue.

 

[nnnnnn]

My issue evolved to P2135 where wrench symbol came on and car would go into limp mode if I stopped the car, turn it off then try to start it and keep driving soon. I replaced throttle body, gas pedal sensor but the P2135 was still coming on although it didn't throw a wrench the moment I turned off the car then try and keep going les than a shortwhile after, so I figured that was progress but then it changed to just going into limp mode the moment I try to get on the gas. Same P2135 code. I suspected it was an electrical issue so I bought new pigtail TPS harness, cut the old ones coming off engine bay and connecting to TPS Sensor. I crimped the wires together very good and then problem went away with P2135. Saved myself labor and diagnosis lol.

Misfire for Cylinder #5 is still there. My installer noticed oil on my spark plugs so long story short, piston for cylinder #5 is done or on its way out most likely. I got a different car for daily.

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