MECHANICAL ASSISTANCE NEEDED (advanced level misfire diagnostic)

[Jeff7814]

I have a 2016 V6 mustang. Only while I'm driving the car will get a flashing check engine light and spike to 20 on the AFR gauge. It generates a p0300, p0301, and p0305 codes.

Current tests completed:
Coil swap from cylinder 4 to 5
Injectors cleaned and tested
Spark plugs replaced and gapped properly
Fuel emptied and replaced with fresh 93

None of those have fixed the misfire and I'm at a loss the car is heavily modified so ford wont touch it and because it only does it while driving I'm not sure what the next step should be.

If anyone has any idea's or questions ill do my best to answer as fast as possible.

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[W.O.T. Stang]

Do you have access to a good scan tool? What are your fuel trims looking like (short term and especially long term). This will point you in a direction as to what the PCM is seeing and adjusting for.

Have you done an in cylinder compression test as well as a relative compression test? Also if you have access to a good borescope with a side/wiggle lens - have a look inside the cylinders. Look for cylinder wear/coolant leakage/valve condition.

The fact that you are hitting 20:1 AFR (according to the PCM output) this points to an extreme lean condition which points towards a fuel delivery issue or too much unmetered air. Are you using the stock MAF? Has it been cleaned? If you have the misfire at idle check for a vacuum leak. But you state this happens while you are driving and this is much less likely.

Im sure others will chime in here as well, but trying to do remote diagnostics is tough, but hopefully we can point you in a direction to help.

 

[Jeff7814]

Do you have access to a good scan tool? What are your fuel trims looking like (short term and especially long term). This will point you in a direction as to what the PCM is seeing and adjusting for.

Have you done an in cylinder compression test as well as a relative compression test? Also if you have access to a good borescope with a side/wiggle lens - have a look inside the cylinders. Look for cylinder wear/coolant leakage/valve condition.

The fact that you are hitting 20:1 AFR (according to the PCM output) this points to an extreme lean condition which points towards a fuel delivery issue or too much unmetered air. Are you using the stock MAF? Has it been cleaned? If you have the misfire at idle check for a vacuum leak. But you state this happens while you are driving and this is much less likely.

Im sure others will chime in here as well, but trying to do remote diagnostics is tough, but hopefully we can point you in a direction to help.

short and long term fuel trims are both pretty steady around exactly 1 the lowest I’ve seen is like.9 in the short and the highest I’ve seen is the long at 1.15 at startup

I haven’t done a compression test because my assumption was if compression was bad the issue would be constant and not coming and going

it’s a upgraded 3 bar ford oem map sensor that I also haven’t cleaned because I felt that would cause more universal issues rather then two random cylinders on seperate sides

I do really appreciate the help

 

[SCP440]

Coulld you have an injector going ? If you can get to the plugs on the injectors pull them off one at a time and see what difference it makes.

 

[Mike Pfeifer]

You should do the compression test. You may have borderline situation that seems ok at idle but goes out of tolerance at load.

Also, please fill us in on what “heavily modded” means.

 

[volvofan94]

Potentially a roller cam follower on the bank 1 side of your engine is wearing out and not opening the intake valve for the correct duration. It looks like the V6 and V8 engines share the same TI-VCT design. I'm guessing your car has roller cam followers and one or maybe 2 of them are out of spec because the roller ball bearings inside the follower have wear on them.

My Mustang had a similar problem; difference was the car had a misfire in cylinder 6. I was hoping for an easy DIY fuel or electrical fix, but after taking it to my local Ford dealership, they found the cam follower was out of spec. The dealership replaced them and the car is running fine ever since.

 

[Jeff7814]

You should do the compression test. You may have borderline situation that seems ok at idle but goes out of tolerance at load.

Also, please fill us in on what “heavily modded” means.

Heavily modded means:
DW400 Fuel pumP
FIC 1000CC injectors
Boundary billet oil pump gear
Manley billet pistons
Manley forged rods
King performance main and rod bearings
ARP Head studs
1 Step colder NGK spark plugs
Precision 6766 turbo
Ford OEM 3bar MAP Sensor
and probably a few other small things im forgetting

 

[Jeff7814]

Anyone can feel free to correct me if i'm wrong but i believe because of the way it misfires its not possible for this to be a mechanical issue. The misfire only happens when i'm driving the car doesn't misfire and then stay running two cylinders down if i continue driving or pull over the car will recover on its own.

It also gets a flashing check engine light but that goes away when it recovers. I think its hitting some kind of safety and cutting fuel to the cylinders but im not sure how to know what that saftey is or how to fix it

Its also worth mentioning that while its misfiring the Short term fuel trims lock at their current value while when im driving the car it regularly moves by .01 up or down multiple times a second

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