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Engine runs rough and codes PO175, PO172, PO351, PO161 and PO141

Tiny
SWEETIE1965
  • MEMBER
  • 2003 FORD F-150
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
Purchased this truck yesterday. The previous owner told me the engine was rebuilt about 6-8 months ago. Drove the truck home with it running rough. It has very little pick up power. It burned about $20.00 gas just to go about forty miles. When I got home, I scanned the truck with a handheld scanner. It gave me the following codes:PO175, PO172, PO351, PO161, AND PO141. According to the previous owner, someone told him the truck needs valve springs replacement. I'm really not sure where to start. I was going to try to do an entire tune up to see if that solves the problem, but I don't want to spend money for nothing. If you know what some or all of these codes have in common, would be greatly appreciated. And how do I go about repairing this truck? Thank you for your help in advance.
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Thursday, October 14th, 2021 AT 7:57 AM

52 Replies

Tiny
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  • MECHANIC
  • 6,383 POSTS
Hello,

So, these are the codes:

P0141 - Oxygen sensor circuit malfunction
P0161 - Oxygen sensor circuit malfunction
P0172 - System Rich Bank 1
P0175 - System Rich Bank 2
P0351 - Ignition Coil circuit malfunction

Just about all of these are fuel / oxygen sensor related.
Possible causes are contaminated mass air flow sensor, faulty fuel pressure regulator, Leaking injectors, EVAP canister purge valve leak, vacuum leak, faulty oxygen sensor etc.

I think the best course of action would be to do a thorough inspection under hood for any fuel and vacuum leaks. Check all the vacuum lines as well as fuel lines. Inspect the fuel pressure regulator.
Do a thorough cleaning off the mass air flow sensor and the throttle body. Check the plugs for fouling. Replace if necessary.

https://www.2carpros.com/articles/throttle-actuator-service
https://www.2carpros.com/articles/mass-air-flow-service

After that you should clear the codes and run the truck and see what all code still exists.
This way you will be able to narrow down the possible issue.

I have attached more details on those codes below.

Let me know of any questions.
Thank you.
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Thursday, October 14th, 2021 AT 8:28 AM
Tiny
SWEETIE1965
  • MEMBER
  • 158 POSTS
The motor oil in the truck smells like gas. Do you think it would be best to change the oil and filter? I have Motorcraft spark plugs and a fuel pressure regulator to replace them.
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Thursday, October 14th, 2021 AT 10:08 AM
Tiny
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Yes, it would definitely be a good idea to change the oil. Typically, you will get fuel in oil when the engine has been running rich for an extended period of time.
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Thursday, October 14th, 2021 AT 10:19 AM
Tiny
SWEETIE1965
  • MEMBER
  • 158 POSTS
Okay. I will change oil and filter before starting the engine, so I don't cause further damage to the engine.
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Thursday, October 14th, 2021 AT 10:57 AM
Tiny
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Sounds good. Let me know how it turns out. Or if you have any questions.
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Thursday, October 14th, 2021 AT 11:08 AM
Tiny
SWEETIE1965
  • MEMBER
  • 158 POSTS
Checked four spark plugs and coil packs, they seem to be in good condition. The plugs didn't have a gas smell to them. The coil packs had resistance of 1-1.5 ohms. Changed the fuel pressure regulator, it made a good difference in the way the truck runs. Would gas smell in the motor oil cause blue smoke to come from the tailpipe? All the codes are gone except the oxygen sensor codes. The previous owner told me all the sensors were changed when the engine was rebuilt about 6-8 months ago. Would gas fumes in motor oil cause blue smoke from tailpipe and slow pick up?
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Thursday, October 14th, 2021 AT 1:26 PM
Tiny
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Typically, the engine will produce blue smoke if it is burning oil (example: due to a leaky piston ring etc).

https://www.2carpros.com/articles/blue-smoke-from-engines-exhaust

Excessive smoke can make the oxygen sensor to not function properly or malfunction and go bad.
Follow this guide to test the sensor:

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

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Thursday, October 14th, 2021 AT 2:00 PM
Tiny
SWEETIE1965
  • MEMBER
  • 158 POSTS
Would a faulty oxygen sensor cause a hard to start condition? The truck runs better since I replaced the fuel pressure regulator, but it's still hard to start and the "get up and go" isn't there. It gradually picks up speed. Once the truck is going, I can smash the gas pedal and most times it will go. Sometimes not though.
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Thursday, October 14th, 2021 AT 2:37 PM
Tiny
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Oxygen sensor does not impact the start up. It could make it run rough afterwards.
Typically, hard start is due to either a fuel or spark issue.
Does it idle rough?
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Thursday, October 14th, 2021 AT 3:06 PM
Tiny
SWEETIE1965
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  • 158 POSTS
It idles fine. It just has slow pick up. Once it gets going its fine. Like about 40 MPH it's fine. Before that it's like slow pick up.
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Thursday, October 14th, 2021 AT 3:18 PM
Tiny
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So, it drives normal past 40 MPH? Normal acceleration?
Is there any noise associated with the slow acceleration?

Any other codes? See if you can scan for historical codes.
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Thursday, October 14th, 2021 AT 3:21 PM
Tiny
SWEETIE1965
  • MEMBER
  • 158 POSTS
No. It has slow pick up until I get to about 40 MPH. After 40 MPH it gets a little bit better. And so on until I reach the speed limit. When I was driving it home last night, I noticed it backfired slightly only one time at about 30 MPH It hasn't done it since then.
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Thursday, October 14th, 2021 AT 4:10 PM
Tiny
SWEETIE1965
  • MEMBER
  • 158 POSTS
No noise is associated with the acceleration. No excessive fuel pump noise or anything like that.
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Thursday, October 14th, 2021 AT 4:10 PM
Tiny
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I wonder if the catalytic converter is clogged. A clogged converter will have this type of slow acceleration as it will have too much back pressure.

Just so we have a clear picture. What have you replaced or serviced so far? And what is the code that you currently have?
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Thursday, October 14th, 2021 AT 6:38 PM
Tiny
SWEETIE1965
  • MEMBER
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I have checked 4 spark plugs which appears to be in good condition with a very faint gas odor, I have changed the fuel pressure regulator, which helped a lot. I have checked 4 of the coil packs, each one has a resistance of 1-1.5ohms, which according to Google is within specs, I have checked the mass air flow sensor and cleaned it out. It's hard to start any light blue smoke is coming from the tailpipe. The codes I get are oxygen sensor codes only. I was going to pull them off and try to clean them up before I replace them. I may be able to get away with cleaning them. The codes are: PO161 and PO141. That's the only codes. What is causing the hard to start condition after the previous owner told me the engine was recently rebuilt? But he may have lied. I can tell you; all the gaskets appear to be new. No leaks anywhere and engine is super clean. I did check the engine oil. It smells like gas, and it did go down some since I drove it home which is about 30-35 miles.
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Friday, October 15th, 2021 AT 5:16 AM
Tiny
SWEETIE1965
  • MEMBER
  • 158 POSTS
I forgot to mention, I also unplugged the PCV valve while the engine was running. There is no blow-by coming from the PCV. There is strong vacuum from PCV hose like normal.
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Friday, October 15th, 2021 AT 6:18 AM
Tiny
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It is good possibility that the issue lies within the oxygen sensor or the circuit.
Inspect the harness for the oxygen sensors. Make sure there is no corrosion, short or broken/damaged wires. This can also be triggered by a damaged oxygen sensor. If the sensor is not getting adequate power due to wiring issue.
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Saturday, October 16th, 2021 AT 9:11 AM
Tiny
SWEETIE1965
  • MEMBER
  • 158 POSTS
I checked everything I can think of. The only thing I haven't checked is the fuel pressure. I can check that to see if it has proper pressure and check for leaks at the same time. I will also check the fuel pump driver module. Everything I checked so far check out. I replaced the oxygen sensor. It was full of black soot so I'm sure it wasn't functioning properly.
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Monday, October 18th, 2021 AT 7:02 AM
Tiny
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Here are the fuel pressure specifications:
Engine Running: 193-310 kPa (28-50 psi)
Key On Engine Off: 240-310 kPa (35-45 psi)

Let me know how it turns out.
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Monday, October 18th, 2021 AT 11:24 AM
Tiny
SWEETIE1965
  • MEMBER
  • 158 POSTS
I wasn't getting any fuel pressure at all but yet the engine would start and run. That's a new one to me. I think maybe the Schrader valve is bad or something. Well anyway, I found the fuel pump relay was not in the proper place, so I put it in its proper place. It started up easy the first time. Ever since then it's back to the same thing. Hard to start. It still idles rough but not quite as bad. I know there is gas in the oil or at least gas fumes in the engine oil. I have some brand new oil I will change it tomorrow. Now I'm leaning towards the fuel pump is weak.
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Monday, October 18th, 2021 AT 3:00 PM

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