Engine problem
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Cross-Country
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From: cheney
Engine problem
I have a 1999 f250 superduty v10 and its throwing the P0171 code, I already changed the fuel filter. I was going to change mass airflow sensor next, but cant find it any ideas, where its at? Also engine runs like it wants to die when in drive or reverse, neutral is fine, any thoughts on that?
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dies
I have a 1999 f250 superduty v10 and its throwing the P0171 code, I already changed the fuel filter. I was going to change mass airflow sensor next, but cant find it any ideas, where its at? Also engine runs like it wants to die when in drive or reverse, neutral is fine, any thoughts on that?
P0171 FORD code possible causes
- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Positive Crankcase Ventilation (PCV)
- Faulty Mass Air Flow (MAF) sensor
- Incorrect PCV hose connection
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Check for anything that could be giving you a vacuum leak - basically anything that lets air into the engine that the MAF doesn't see. Cracked intake hose, the big rubber plug on the bottom of the air box fell out, bad PCV valve, etc.
Then, get a fuel pressure gauge, hook it to the fuel rail and see what pressure you get at idle and with the key on but engine not running. Cycle it a few times between off and on, to give the fuel pump a chance to build pressure. Then, if you can find a gauge with a long enough hose, see what it does under load, say accelerating up to highway speed, but with your foot to the floor.
At idle, it should be 28-30 lbs, under load (or engine not running, with key on) it should be 38-40. Approximately.
Then, get a fuel pressure gauge, hook it to the fuel rail and see what pressure you get at idle and with the key on but engine not running. Cycle it a few times between off and on, to give the fuel pump a chance to build pressure. Then, if you can find a gauge with a long enough hose, see what it does under load, say accelerating up to highway speed, but with your foot to the floor.
At idle, it should be 28-30 lbs, under load (or engine not running, with key on) it should be 38-40. Approximately.
Fleet Owner
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To my eye that looks like the vacuum line running from the intake manifold to the HVAC system controls. I've dealt with a few E-Series where the leaking vacuum reservoir prevented those controls from working but never triggered a DTC P0171/P0174. FWIW that line is post-MAF so in theory could be triggering that DTC but I wonder if the IAC isn't giving you problems?
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From: cheney
It started the hesitating while i was at idle in drive and park, I had to put it in neutral and rev the engine to keep it running, then I cleaned the IAC and replaced a vacuum line now it does it just a little in idle and now while I am driving when I press the gas.
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From: Reynoldsburg, Ohio
Unfortunately that's not a quantifiable comment so kinda tough to offer advise based on that alone. Have you checked fuel pressure as already advised? Have you had the OBD-II system scanned for DTC's?
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I'd concentrate on all vacuum lines attached to intake, including plugging that red vacuum line, even if it is small.
How is the PCV hose going into the intake (especially at the tight bend)? Ensure no cracks anywhere on it.
From the Ford Powertrain Control/Emissions Diagnosis service manual:
- Check intake air system for leaks, obstructions and damage
- Check air cleaner element, air cleaner housing for blockage
- Verify integrity of PCV system
- Check fuel delivery system and filter for restriction
- Check for vacuum leaks
If no issues found above, it takes you to a MAF diagnosis chart. At that point, as others have already mentioned, you'll want to try cleaning the MAF first.
You may also want to try to pull the battery cable for a few minutes to reset the computer just in case.
How is the PCV hose going into the intake (especially at the tight bend)? Ensure no cracks anywhere on it.
From the Ford Powertrain Control/Emissions Diagnosis service manual:
- Check intake air system for leaks, obstructions and damage
- Check air cleaner element, air cleaner housing for blockage
- Verify integrity of PCV system
- Check fuel delivery system and filter for restriction
- Check for vacuum leaks
If no issues found above, it takes you to a MAF diagnosis chart. At that point, as others have already mentioned, you'll want to try cleaning the MAF first.
You may also want to try to pull the battery cable for a few minutes to reset the computer just in case.
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