SOURCE: po171 po172 po174 po175 ???
If the fuel pressure was low enough to give lean codes then u would have a loss of power that you would easily notice, you say you checked for vacuum leaks, did you use a can of carb spray or a bottle of propane? it only takes a very small leak to trigger the codes, spray carb spray around the intake area, see if the engine sound changes, this will indicate a leak,
SOURCE: 1996 ranger 4.0 codes po171 and po174 come up on the screen
Check for vacuum leaks, especially the intake manifold gaskets. If those are o.k., clean the Mass air flow sensor.
Barring any vacuum leaks, P0401 is indicative of a bad EGR valve. Hope this answers your question. Best of luck.
Greg
SOURCE: 05 mercury sable check engine po174
You has a vacuum leak on the engine.
In order to troubleshoot this, you must start with a clean engine wipe down.
The major offender parts are
air intake gasket on the manifold
air tube after the mass air flow sensor
rubber seal under idle air control IAC motor
===
Warm up the engine for 15-20 minutes (LEAVE THE engine at idle) then spray a little Barmen carburetor clear on the potential air leak location (ONE AT A TIME) and listen for a surge in rpm.
If the engine speed go higher that's mean the carburetor clean (ADDITIONAL FUEL) got into your engine and that's the gasket you need to change.
There may be multiple leaky spots so take your time and check all rubber gaskets,sensor and hose that are lead into the intake manifold.
When you finish fill up with one tank of Chervon to clean out the injectors.
Please post more information after your inspection.
can cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
Possible solutions include:
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