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Discussion Starter · #1 ·
2017 Focus RS with 61K miles. Dealer replaced the head gasket after the history of minor oil leaks since they changed the head head gasket under recall years ago.

A few cold starts after, CEL lit up - P0300, P0171. LTFT 28-29% on idle, dropping to about 20% on 3K RPM.

Brought the car back, dealer checked for vacuum leaks, replaced the O2 sensor, redid intake manifold seal... None of this helped, still getting misfires on warm up, LTFT still 29%. STFT hovering around 0%.

I tried looking for vacuum leaks myself (with a can of propane ). Cleaned MAF. No luck.

The coolant level is stable after about 300 miles since the head gasket job, car runs fine.

The dealer has been pretty cooperative and they are working with Ford to troubleshoot, but at this point they seem to be out of ideas. This has been dragging for a couple months. Any help?
 

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HPFP sensor and or fuel injectors. Many people here have had fuel injector issues after HG changes for some reason. They are pretty cheap and easy to replace. This engine is marginal on idle stability so it doesn't take much to tip it over the edge.
Phil
 

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Discussion Starter · #3 ·
HPFP sensor and or fuel injectors. Many people here have had fuel injector issues after HG changes for some reason. They are pretty cheap and easy to replace. This engine is marginal on idle stability so it doesn't take much to tip it over the edge.
Phil
Cylinder 4 seems to be the only one not getting misfires. Should I try moving the injectors around before replacing them?
 

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Discussion Starter · #4 ·
Cylinder 4 seems to be the only one not getting misfires. Should I try moving the injectors around before replacing them?
Forgot to mention, the dealer did a bunch of other stuff to the car as a part of the head gasket job. Including changing the timing chain. (Forgot the reason for that, didn't care at time because it was under ESP). Does this change anything?
 

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Forgot to mention, the dealer did a bunch of other stuff to the car as a part of the head gasket job. Including changing the timing chain. (Forgot the reason for that, didn't care at time because it was under ESP). Does this change anything?
Well the timing chain needs to come off for the job anyway. Why it needed replacement at that mileage is anyone's guess as it should have been fine. Sometimes mechanics stuff things up and ruin parts and just replace them an cover up the mistake.
BTW first thing you should do is a "static misfire correction" as per the shop manual. Sorry should have mentioned that before. The dealer will need to do this though.
After the static misfire correction if the issue persists then try injectors. You could just do the #4 but the whole rail needs to come off anyway and they aren't that expensive and at your mileage it's probably a good idea to either have them cleaned anyway. Most people don't bother cleaning them as for the cost replacement is the better option.

Phil
 

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Discussion Starter · #6 ·
Well the timing chain needs to come off for the job anyway. Why it needed replacement at that mileage is anyone's guess as it should have been fine. Sometimes mechanics stuff things up and ruin parts and just replace them an cover up the mistake.
BTW first thing you should do is a "static misfire correction" as per the shop manual. Sorry should have mentioned that before. The dealer will need to do this though.
After the static misfire correction if the issue persists then try injectors. You could just do the #4 but the whole rail needs to come off anyway and they aren't that expensive and at your mileage it's probably a good idea to either have them cleaned anyway. Most people don't bother cleaning them as for the cost replacement is the better option.

Phil
ForScan has "Misfire Monitor Neutral Profile Correction" and I may or may not have run it the other day. I assume this is the same as "static misfire correction"? The LTFT is still 29% on idle and looks like I have another lean code maturing in ECU, so it didn't seem to have helped.

I plan to do a smoke test myself to rule out the vac leak next, just to be sure. After that, I will take the car back to the dealer and see if they would be willing to do injectors and fuel pressure sensor replacement. The procedure looks easy enough for DIY, but I will likely be forfeiting any claims on potentially bungled head gasket replacement if I take the engine manifold off.
 

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ForScan has "Misfire Monitor Neutral Profile Correction" and I may or may not have run it the other day. I assume this is the same as "static misfire correction"? The LTFT is still 29% on idle and looks like I have another lean code maturing in ECU, so it didn't seem to have helped.

I plan to do a smoke test myself to rule out the vac leak next, just to be sure. After that, I will take the car back to the dealer and see if they would be willing to do injectors and fuel pressure sensor replacement. The procedure looks easy enough for DIY, but I will likely be forfeiting any claims on potentially bungled head gasket replacement if I take the engine manifold off.
And they would know how?

Phil
 

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Normally when i run into p0171's it's from a leak before the primary o2 on these as they are speed density. So look at where your downpipe bolts up to the turbo and where the turbo bolts up to the head.
 

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Discussion Starter · #10 · (Edited)
Normally when i run into p0171's it's from a leak before the primary o2 on these as they are speed density. So look at where your downpipe bolts up to the turbo and where the turbo bolts up to the head.
Tried a smoke test, there doesn't seem to be a vacuum leak anywhere.

Is showing the smoke machine to the intake immediately past the airbox the right way to do it?

Like this video here:
.
 

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Discussion Starter · #12 ·
Do you have a cobb accessport? What does your boost reading report at idle?
Don't have Accessport. OBDFusion shows -10.7psi, which seems to be normal?



BUT! I was reading up on fuel trims (there is 1st time for everything) and staring on my O2 PID data...

O2S11 seems to be stuck at > 1v. O2S12 is around 0.73v.

I am using ForScan/OBDLinkEx for this. It doesn't have upstream O2 voltage per-se, there is current, resistance and O2S11_IMPED voltage which seems to be calculated. So, this O2S11_IMPED alternating between 1.01V and 1.02V. The resistance shows 0 0hm. Is this an indication that the O2 sensor is fu.. damaged?

The dealer actually replaced the O2 sensor "because it wasn't working correctly". But given that they gave me back the car with +30% fuel trims, I wouldn't be surprised if they didn't bother to check if the sensor was actually working after they swapped it.
 
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