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Discussion Starter #1
Hello everyone, Got a long one here so thanks if you read until the end!

Car recently had a refreshed long block installed by myself. Runs great but cant seem to nail down this issue. The only issue is with idle. The car drives perfect otherwise.

Car misfires at idle, video below. LTFT at idle is +25 to +28. If car is left idling for too long P0300 (random misfire) code is thrown. P0171 (system too lean bank 1) is always throw


I smoke tested the vacuum system. Balloon in intake, smoke machine plugged into the vacuum pump first, then the vacuum line going to the solenoid for the wastegate second. No visible leaking.

I suspected bad gas since I had a few gallons of old e85 I diluted with 10 gallons of 91 non oxy in the tank. Fuel trims under load were +20 ltft while cruising in 6th at 60mph. 0 fuel trim at WOT. I ran the car down to half a tank babying it and added 2 more gallons of 91 non oxy to see if they got better. Fuel trims under load dropped it +15 in 6th at 60mph. Still +25 at idle with the misfire for the next 80 miles or so.

I drove about 20 more miles and when I got home, +28 LTFT -28 STFT. Misfire was gone! Only to return the next morning with +25 LTFT +0 STFT

Ran the tank down to about 1 gallon. Topped off with 91 non oxy again and fuel trims in 6th at 60 dropped to +10. Idle was still +25 ltft and misfire is present.

Not sure where else to look here. Fuel pressure on the high and low side looks good. No drivability issue or odd noises besides at idle. I did try a bottle of fuel injector cleaner in case an injector was clogged and not firing at idle.
 

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Some things to consider: Check O2 sensors, check fuel injectors, replace high pressure fuel sensor.

Why the reason for a new longblock, and what mods again?
 
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Hello everyone, Got a long one here so thanks if you read until the end!

Car recently had a refreshed long block installed by myself. Runs great but cant seem to nail down this issue. The only issue is with idle. The car drives perfect otherwise.

Car misfires at idle, video below. LTFT at idle is +25 to +28. If car is left idling for too long P0300 (random misfire) code is thrown. P0171 (system too lean bank 1) is always throw


I smoke tested the vacuum system. Balloon in intake, smoke machine plugged into the vacuum pump first, then the vacuum line going to the solenoid for the wastegate second. No visible leaking.

I suspected bad gas since I had a few gallons of old e85 I diluted with 10 gallons of 91 non oxy in the tank. Fuel trims under load were +20 ltft while cruising in 6th at 60mph. 0 fuel trim at WOT. I ran the car down to half a tank babying it and added 2 more gallons of 91 non oxy to see if they got better. Fuel trims under load dropped it +15 in 6th at 60mph. Still +25 at idle with the misfire for the next 80 miles or so.

I drove about 20 more miles and when I got home, +28 LTFT -28 STFT. Misfire was gone! Only to return the next morning with +25 LTFT +0 STFT

Ran the tank down to about 1 gallon. Topped off with 91 non oxy again and fuel trims in 6th at 60 dropped to +10. Idle was still +25 ltft and misfire is present.

Not sure where else to look here. Fuel pressure on the high and low side looks good. No drivability issue or odd noises besides at idle. I did try a bottle of fuel injector cleaner in case an injector was clogged and not firing at idle.
Is it worse cold or fully warm?

Ciao
 

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Discussion Starter #5
fuel filter?
Will look into this tonight since it's a cheap diagnosis.


Some things to consider: Check O2 sensors, check fuel injectors, replace high pressure fuel sensor.

Why the reason for a new longblock, and what mods again?
02 sensors should throw their own codes right? Not sure how to check fuel injectors short of sending them out for cleaning. Isn't the high pressure sensor integrated into the pump?
Car had a built long block installed previously. Returned to stock. 0 performance modifications as of now.


Is it worse cold or fully warm?

Ciao
No change really. The one time the fuel trims went +28 and -28, fixing the misfire the car was warm but it has never done that since. Another 150 miles has been driven since then.
 

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Will look into this tonight since it's a cheap diagnosis.



02 sensors should throw their own codes right? Not sure how to check fuel injectors short of sending them out for cleaning. Isn't the high pressure sensor integrated into the pump?
Car had a built long block installed previously. Returned to stock. 0 performance modifications as of now.




No change really. The one time the fuel trims went +28 and -28, fixing the misfire the car was warm but it has never done that since. Another 150 miles has been driven since then.

and

 

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Discussion Starter #7

and

Both of these had a P2195 code and drivability issues. The AFR on my car is stable with the fuel trims the ECU is doing. I have 0 driveability issues, just the misfire at idle and high fuel trims.

Jessica Livernois thinks it's the crankshaft position sensor so I ordered a tool and will be realigning the tool and taking it in for a neutral misfire profile correction, again. PITA to get it in for the programming but she's a damn wizard with these cars so we will see.

If that doesn't work my next step will be replacing the front O2 sensor and low pressure fuel pressure sensor I guess. 95% sure neither of these are the issue however.
 

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Both of these had a P2195 code and drivability issues. The AFR on my car is stable with the fuel trims the ECU is doing. I have 0 driveability issues, just the misfire at idle and high fuel trims.

Jessica Livernois thinks it's the crankshaft position sensor so I ordered a tool and will be realigning the tool and taking it in for a neutral misfire profile correction, again. PITA to get it in for the programming but she's a damn wizard with these cars so we will see.

If that doesn't work my next step will be replacing the front O2 sensor and low pressure fuel pressure sensor I guess. 95% sure neither of these are the issue however.
Can you not do the static misfire correction with an OBD connector and an Iphone/android app?
Yes you should have used the setting tool to do the crank sensor. You also need to restrain the crank pulley when you torque up the bolt and not have the alignment pin in otherwise the pulley can move and the timing will be wrong. You can put the alignment pin in and count the teeth on the pulley from the gap and see if you are out.

Ciao
 

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Discussion Starter #9
Can you not do the static misfire correction with an OBD connector and an Iphone/android app?
Yes you should have used the setting tool to do the crank sensor. You also need to restrain the crank pulley when you torque up the bolt and not have the alignment pin in otherwise the pulley can move and the timing will be wrong. You can put the alignment pin in and count the teeth on the pulley from the gap and see if you are out.

Ciao
Adam from Tune+ set the timing on the engine since he assembled the longblock for me.

Multiple techs have told me with the pin in the crank pulley to the valve cover they have always been able to eyeball it without issue. But Jessica has far more experience than either of them so it's worth a shot. The correct tooth does line up perfectly with the sensor once the bolt is placed through the pulley into the timing cover but I guess if it's off by even a little but it could cause issues.

I don't believe you can do the neutral misfire profile correction without a ford scan tool. I could be wrong and would be happy to learn that I am if you know of another way. Im using a OBD Link MX and the Torque Pro app.
 

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Discussion Starter #10 (Edited)
Update. It was the front O2 sensor

Changed the LPFP pressure sensor, fuel rail pressure sensor, purge valve, Redid all the vacuum lines for the turbo and ran through a tank of gas until I nearly stalled out and filled up with fresh 93 octane. The fuel trims did get a bit better under load but the ltft was still maxing out at idle and throwing P0171

Changed the Front O2 sensor. LTFT is now +5-8% at idle and P0171 nor P0300 have returned since. I waited until all the emissions monitors had readied to claim victory.

There is still a misfire at idle but it is MUCH less frequent. Once every 10 seconds or so and it has not thrown any codes. I'm calling it there. I took the only logical step I could after and I killed it with fire.

 
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