Good Morning All,
I am new to the group and have had a lot of issues getting this Mustang Registered. I bought the vehicle not knowing it was flagged by the state ref and now I have reverted everything back to stock to get the title transferred. The car runs with a rough idle setting intermittent misfire codes at times. I have read through countless forums and ran many diagnostic tests. It seems this can be a variety of issues based on what I have read and seems to be pretty common amongst all the 2011-2014 Mustang owners out there. Below is a synopsis of everything I have done to isolate the issues which I still have.Purchased Condition:

Boss 302 Intake Manifold

GT500 Injectors 52lbs

SCT Tune

Catalytic Convertor Delete

JCT Intake

Borla Exhaust

4.10 Rear End Gears

- Flagged for Smog Referee in order to register.

Reverted Parts to stock for Smog Ref:

Installed Parts in order timeline:

· Used Factory Intake Manifold

· Used Factory Intake

· Ford La Mesa Re-flashed PCM to stock

· Ed Hanson Muffler shop Installed CARB Catalytic Convertors purchased from Ford

· Bosch Spark Plugs installed and gapped to .52"

· New Bosch GT Injectors 37lbs, New Upstream O2 Sensors, New Crank Shaft Position Sensor

11/2022 - Upon pick up from Ford after Re-Flash PCM listed random multiple misfire. Swapped spark plugs and injectors. Cleared codes. PCM listing misfire on number 6. Monitored with scan tool and it shows 4,6,8 misfiring but no CEL.

2/2023 – Swapped Ignition Coils around to see if misfire changed locations. Still showing misfire on cylinder 4, 6, 8. Car did not have MIL but misfires showing on misfire monitor of scan tool.

3/2023 – Performed Compression Check on all cylinders all cylinders within 148-150psi. Performed Misfire Monitor Neutral Profile Correction. Still showing misfires mainly on 4,6,8. 6 with the most misfires per cycle, no CEL.

3/2023 – Performed leak down on cylinder 6 with 6 on TDC. Used magnet stick to get cylinder to TDC rotating crank by hand. Shows within acceptable range on gauge. No air seems to be getting past rings or valves head gaskets etc.

3/2023 – Replaced Crank Sensor. Although started car and it still runs the same. PCM logged MIL and P0300 Random Multiple Misfire at idle. Performed Misfire Monitor Profile Correction. No change in idle.

3/2023 – Inspected o2 sensor holding clips were broken off indicating that the transmission was removed at some point without proper o2 sensor clip removal. Downloaded wiring diagram and inspected to verify upstream 2 sensors were plugged into correct banks. It appears they are in the correct locations.

3/2023 – Replaced upstream o2 Sensors. Old O2 sensors have some black but mainly white soot. Sign of running lean? This build up was mainly from running previously as the stock tune had only seen about 20 start-ups so I don't think this was fro my current stock tune. Car seems to respond better with throttle input. Car still running rough at idle. No CEL.

3/2023 – Performed Fuel Pressure check with inline fuel pressure gauge. Fuel Pressure was steady at 55psi at idle. Ignition off Fuel pressure dropped to roughly 40 psi.

3/2023 – Performed smoke test. Inserted smoke line in inlet in intake tube. No smoke escape. Removed Air Filter cover to verify smoke was present in system. Air Box full of smoke. Inserted smoke line after throttle body into intake manifold PCV Port to verify smoke was entering manifold, smoke for 10 minutes. No smoke escape anywhere on motor. Removed throttle body and verified intake manifold was full of smoke. Observed some build up around throttle body plate, cleaned throttle body with throttle body cleaner. Reinstalled throttle body. Car still runs rough at idle. No CEL since Misfire Monitor Profile Correction performed after Crank Sensor Change.

3/2023 - Noticeable tick at idle. When car is misfiring with Clutch disengaged engine lopes a little harder. With clutch engaged car still misfires but does not shake as bad with the clutch disengaged.

Summary:

Car ran fine with aftermarket parts.

Car seems to run fine on cold start open loop. Closed loop car runs poorly at idle through roughly 1800-2000 rpm. 2000+ rpm car seems to run smoothly. Driving the vehicle there is no loss of power or rough running.

Could this be a VVT Solenoid issue? Cam Phaser Issue?

 

Try doing the crank relearn process. You mentioned that you discovered the transmission had been removed, and when you separate the engine and transmission you have to do the relearn process. If it isn't done, you will get things like random misfire.

 

I did the Crank Relearn twice. Still the same.

 

Back to basics.

Have you confirmed the throttle body is stock? With those mods, I suspect an upgraded (higher flow) throttle body was also installed.

What are the actual codes you are getting for the misfires?

There are two types, P030x is a generic misfire code usually related to a mechanical issue like cylinder leak, bad plug, dirty injector, timing etc.

The second type that is less well know is P035x. This is related specifically to a coil or coil wire failure and is produced when the PCM doesn't get the expected voltage/resistance value back from the coil.

Do you have a hand held with live data capabilities?
What do your Long Term Fuel Trims look like?

Rev the engine until it gets to misfire and hold it. What do the Short Term Fuel Trims look like when it's misfiring? What do the values on the O2 sensors look like when it's misfiring? What does the MAF/MAP value look like when it's misfiring? If Short term goes very Positive while you are holding RPM (maxes out even), you have a lean condition in the car meaning more air than fuel is present. Also, the O2 sensor would be reading very negative

O2 sensor values are between 0.1v to 0.9v with 0.1 being Lean and 0.9 being rich. Typical value at warm idle is around 0.45v. The injectors will go the opposite direction of the O2 sensors. If the sensor is reading lean, the injector will open up as much as possible (show '+' ) as the injector is dumping in as much fuel as it can to correct the lean condition. If the O2 sensor is showing Rich (close to 0.9v) the injector values will show ('-') as the injector shuts down to reduce the amount of fuel being used.

In short,
STFT Bank 1 and 2 at a stead RPM will show high values + for lean conditions and high values - for rich conditions
O2 sensors at a steady RPM will show closer to 0.1v for lean conditions and closer to 0.9v for rich conditions.

The MAP/MAF sensor is what reads the air density. If Throttle body was changed/modified it will throw all off the calculations by the PCM off because it changes the flow characteristics of the intake. The PCM It uses the MAP/MAF values to adjust the fuel table at various RPM's based on the signals from the O2 sensors. If values in used calculations are erroneous, you end up with all sorts of problems.

I suspect your bank 2 readings will be very different from your bank 1 readings since Bank 2 has two cylinders misfiring.

 

I will get it on the scan tool and see if I can pull the live data. Thank you for your detailed response.

 

This site looks pretty good but how do they rate Mustangs?

 

Update: Pulled Driver Side Valve Cover. #6 Exhaust Valve Spring is Broken.

 

Yes it was the #6 Exhaust valve spring. It was broken and the valve was floating with a loose rocker. Although when performing a compression and leak down test it checked out fine as with pressure in the cylinder it held the valve closed. It was an expensive fix since the cams and timing cover timing chain etc all had to come off.