'15 F-150 2.7L, P0299 that won't go away

Tyler Technician Kansas Posted   Latest   Edited  
Resolved
Driveability
2015 Ford F-150 XL 2.7L (P) 6-spd (6R80)
P0299 — Turbocharger/Supercharger "A" Underboost Condition
P1548 Air Filter Restricted

Good Morning Diag​.​net Hoping you can offer us some insight on this F-150 that refuses to be fixed.

Initially came in with a complaint of low power, stored P0299 and P1548 that mature to Current on a test drive. It's really not all that low on power, but the PCM goes into limp mode and wide opens the wastegates once P0299 goes current. Becomes an NA engine at that point.

Tested for boost leaks, found none. Found that the MAP, throttle inlet pressure sensor and wastegate pressure sensor all agree KOEO. Tested for excessive exhaust backpressure with a gauge AND dropping the exhaust. No change. Checked for fuel delivery at WOT, both upstream air/fuel sensors go to 12:1. Verified VVT actual matches desired at all times. Wastegates can be controlled manually with a vacuum pump and with the scan tool. All hose routing appears correct.

Found excessive oil in the charge air cooler and piping, coming from the left turbo. Replaced both turbos with the CAC, bypass valve and wastegate solenoid. Problem remains. Oops.

The other interesting symptom is the 'hooting' noise it makes occasionally during WOT or heavy load. Kinda reminds me of the old Ford cars with IAC noise? The lack of boost and the noise don't always coincide, but the coincide often enough that I think they're related. The noise sounds like it's coming from the drivers side, but it's very tough to tell, as it can't be reproduced in the bay.

Almost forgot to mention, we can induce an overboost condition by pinching off the hose from the wastegate solenoid to the wastegates. This suggests that the turbos are capable of producing boost.

P1548 has not returned after CAC and turbo replacement.

Again, we'd appreciate any suggestions or ideas you have. Scan data and screenshots are available upon request. Thanks for your time!

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LaMont Owner/Technician
Ohio
LaMont Default
 

This may not apply to your vehicle, but I just had a Ford truck with 6.7 that had this code last week. It would not pass the key on engine running test. I ended up finding that there was not enough vacuum to fully open the wastegate. I'd suggest teeing in a vacuum gauge to make sure you have enough vacuum. If you search (Turbo underboost condition after turbo replacement) you can see my detailed…

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Tyler Technician
Kansas
Tyler Default
 

I like your thinking here, sir. I'll definitely check out your post. Thanks!

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Edward Owner
Texas
Edward Default
   

Tyler Sounds like a leaking flow tube...🤔 P0299 - Turbocharger/Supercharger A Underboost Condition Description: This DTC sets when the actual throttle intake pressure is less than the desired throttle intake pressure by 27.6 kPa (4 psi) or more for 5 seconds. A minimum throttle intake pressure (TIP) PID reading during engine operation indicates an underboost condition. Possible Causes: -…

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Jared Diagnostician
Maryland
Jared Default
 

I dont want to be too obvious, or basic... but have you replaced or checked the air filter?

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Gary Technical Support Specialist
New York
Gary Default
 

- Hi Tyler Check for excessive exhaust back pressure, unable to breath will cause a under boost condition. Has a 3.5 in a Mustang with the same it was the 3rd cat not the front 2 causeing the problem

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Marlin Technician
Oregon
Marlin Default
 

You should read a post before replying to it.

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Inappropriate
Mark Owner/Technician
California
Mark Default
 

I read a case earlier on a GM that had similar condition. Visibly clean air filter & only 6 months old. Air filter OEM or High quality aftermarket (Motorcraft, Denso). I've had 3 in the last year.

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Thanks
Tyler Technician
Kansas
Tyler Resolution
   

Many thanks to everyone that took the time to reply! It's actually fixed now, but I'm very embarrassed to say how. After lots of leak testing, more sensor rationality checks, and following the Ford flow chart all the way to the end, we were still nowhere. On one frustrated test drive, the P1548 decided to return. On a WAG, I decided to leave the air filter out of the filter box and drive it…

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Jared Diagnostician
Maryland
Jared Default
 

It would have been embarrassing if you had given up, and send it to the dealer. ;)

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Edward Owner
Texas
Edward Default
 

Tlyler We all been there brother, what's counts is learning from our mistakes... Great fine 🤠

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Agree
Eric Owner/Technician
Wisconsin
Eric Default
 

Just think how easy it will be the next time!

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LaMont Owner/Technician
Ohio
LaMont Default
 

Good to know. Your post may help someone else in the future with the same problem.

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Paul Mechanic
Illinois
Paul Default
 

Glad you shared and admitted the seemingly simple fix. I know a few shops that would have never admitted what some would say is/was an easy fix (hindsight is always that way). It did take some out of the box thinking and I'm sure all of us who read this either learned something or reinforced past lessons/concepts . Good job.

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Marlin Technician
Oregon
Marlin Default
 

Excellent information! Not all things are apparent, which is why we need to test. At least it wasn't just a dirty or incorrect filter. ;-)

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Geoff Diagnostician
Hawaii
Geoff Default
 

Wow, that's crazy! Those kinds of things are broken on every car I see out here, so if I hadn't read this, I would have never thought of that for sure. Great one!

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Richard Technician
New York
Richard Default
 

Great job, nothing to be embarrassed about!

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Scott Manager
California
Scott Default
 

Thanks for the followup in this Tyler. I suspect that you feel pretty good about solving the issue. Question, did you log and save any of the data before and after that you’d be willing to share? I’d sure like to have a look if possible. Thanks, Scott

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Tyler Technician
Kansas
Tyler Default
 

Sure did, Scott. I'll post them up this afternoon.

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Tyler Technician
Kansas
Tyler Default
   

Before any repairs: scanshare​.​io/share/uodv4_K7… After turbo replacement and clipping down the intake: scanshare​.​io/share/8pwaiAWC… Apologies that the PIDs aren't the same between the captures. The worst part is that I was actually on the right track, just looking in the wrong place. Before any repairs, I could force the wastegates open and see just the breathing of the engine itself. I…

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Mark Owner/Technician
California
Mark Default
 

All that matters is you fixed it and shared, so others can fix their customer vehicles.

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Caleb Diagnostician
Indiana
Caleb Default
 

Wow glad you got it man!!

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