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Check engine light, code PO173

Tiny
KIMZOC
  • MEMBER
  • 1995 FORD F-150
  • 5.0L
  • V8
  • 4WD
  • MANUAL
  • 140,000 MILES
Replaced plugs, wires, cap, rotor, coolant temperature sender, MAP, intake manifold gaskets, TP sensor, the only one o2 sensor in truck has been replaced, computer, air sensor, injectors, maybe more. Found one vacuum leak at heater control, tried blocking off PC vacuum hose at intake,

Runs rich, smells like fuel, uses lots of fuel.

Really would like to figure this out.
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Monday, September 28th, 2020 AT 6:42 PM

7 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

The code indicates a too rich or too lean fuel mixture. Based on what you described, it sounds too rich.

Have you checked fuel pressure? Here is a link that shows how it's done:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

The specs are listed in pic 1.

Do this and let me know the results.

Joe
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Monday, September 28th, 2020 AT 6:56 PM
Tiny
KIMZOC
  • MEMBER
  • 4 POSTS
Replaced fuel pump, cleaned tank, replaced fuel filter and replaced fuel regulator. Koeo and koer pressure is good at 33lbs idle.
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Friday, October 2nd, 2020 AT 7:52 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Okay,

The pressure is perfect. Next, when you checked pressure, did you pay attention to fuel pressure drop off? We may have an injector or injectors leaking.

Let me know.
Joe
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Sunday, October 4th, 2020 AT 4:58 PM
Tiny
KIMZOC
  • MEMBER
  • 4 POSTS
Hi Joe. Thank you. When running pressure is solid stable at 35lbs spikes up to 40ish when throttled. When not running pressure dropped to 32psi but did not drop from there. Within the 45 minutes I had tester on it.
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Sunday, October 4th, 2020 AT 6:51 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Are you certain there are no engine vacuum leaks? The code could indicate too lean or rich.

Here is a link that explains how to check for a leak. Also, I need to know if there is an exhaust leak at the manifold.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know.
Joe
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Sunday, October 4th, 2020 AT 7:48 PM
Tiny
KIMZOC
  • MEMBER
  • 4 POSTS
Hi, thanks again. There are no exhaust leaks it's nice and quiet. I found 1 leak at heater control passenger hood hinge. I blocked off PCV at intake. I squirted starting fluid around all vacuum hoses joins and intake with no rpm difference. I will look at the article and use the vacuum gauge I bought just today then get back to you. Thanks
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Sunday, October 4th, 2020 AT 8:24 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

That sounds like a plan. If by chance you have a live data scan tool, check the short term fuel trims so I have an idea if it is rich or lean. That may help our focus. Also, if you can do this, also check the ECT (engine coolant temperature sensor) reading and let me know if it seems relevant to the engine/ambient temperatures experienced.

Let me know.
Joe
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Monday, October 5th, 2020 AT 7:29 PM

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