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Old 11-14-2020, 08:10 PM   #1
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Issues with a PO171 code? 5.4L

Keep having issues with a PO171 code, seems to happen during startup/at idle.

Here is the freeze frame data, anyone else have this issue and what was the fix?

2000 5.4L 2V

https://drive.google.com/file/d/1HoL...ew?usp=sharing

https://drive.google.com/file/d/13Fr...ew?usp=sharing

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Old 11-14-2020, 08:24 PM   #2
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If the sensors have never been replaced, I’d recommend replacing my both forward sensors at this point. After a whole, the heater elements wear out and don’t get hot enough, or hot at all. The sensing part does need to be hot to properly respond.

Once the sensors are confirmed good, the next most likely cause is broken manifold bolts, which lets air suck IN (due to the Venturi effect) when the manifold forms gaps when it’s cold.

It possible low fuel pressure can trigger this code, but during high load, not during startup. But... good time to think about the fuel filter if it’s been more than 30,000 miles.
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Old 11-14-2020, 08:32 PM   #3
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Thank you for the reply, I'll give the fuel pressure a check and poke around the exhaust manifold. The van runs great for having 300K, but this code randomly come back every 1500-2000 miles.

I've done the following pretty recently,

Coils
Plugs
PCV + Supply Hose
Fuel Filter
Air Filter

I need to clean the MAF and test the pressure, would love to find the culprit before dealing with the exhaust/intake manifold.
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Old 11-14-2020, 08:51 PM   #4
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FWIW Ford recommends doing the forward sensors every 100k.
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Old 11-15-2020, 06:46 AM   #5
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300k and it runs fine? Sounds like it's time for the black tape CEL fix.
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Old 11-15-2020, 07:28 AM   #6
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Do you keep the scan tool connected as the engine goes into closed loop operation? If so what happens to the LTFT's at that point? I have an occasional DTC showing one of the catalytic converters is not within spec or threshold of efficiently. I'm told that can be due the sensors themselves or the cats are beginning to fail. FWIW I have about 165K miles on an '05 E350 with 5.4 motor.

The engine has just about 20K miles but the exhaust system is factory original.

When I watch my Fuel Trims I seem to run a bit negative while in the LTFT's, STFT's switching as they should.

I would maybe run your data again while driving, coolant warm enough to open the thermostat.

Also here's a video I've found very informative about Fuel Trims---this guy is one great teacher! If you're not careful you can spend a lot of time watching his presentations!
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Old 11-15-2020, 03:18 PM   #7
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Thank you for all the responses, I have a reader on to monitor most of the time so I will keep an eye on that.

It has 300K, but was a fleet vehicle before it got to me so with the way it drives and shifts has me thinking its not the original motor or transmission.
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Old 11-15-2020, 03:46 PM   #8
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Why wouldn't you think they're original? The 5.4L easily goes 500k+. And... You probably have the 4R100! After 2001 they downgraded the 5.4L to the 4R75. My 4R100 hasn't been touched since the factory with 493,000 on the ODO. Pan has only been off twice, plus a few more "bucket flush" fluid services.
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Old 11-15-2020, 03:54 PM   #9
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Honestly, you could be right.

We've been trying to get the service records just to know what's coming up repair wise down the road.

Really appreciate the replies to this.
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Old 11-15-2020, 04:08 PM   #10
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Quote:
Originally Posted by JWA View Post
Also here's a video I've found very informative about Fuel Trims---this guy is one great teacher!
Great videos, thanks for the link............
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