Question about 1999 Ford Windstar

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Check engine light keeps coming up with same OBD-II codes

PO171 and PO174 "System adaptive fuel too lean (Bank 1)" and "System adaptive fuel too lean (Bank II)" The first time this happend I was told by the Ford dealership that I had an upper intake vaccum leak and that I had to replace the upper intake gasket and the 6 port seals. I did this and my problems went away for about 8 months. Now I'm getting the same codes with the new gaskets. The shop said it could be a Mass Airflow Sensor, but those are expensive if it's not the problem. I've replaced the PCV valve and the fuel filter in the past year. I did new plugs 2 yrs ago and I've installed a K&N air filter. Could my problem just be a leaky hose or something? What would cause both banks to lean out? It has started Idling a little funny at times and it surged the other day. Do I need to dig back into the Intake or is it an MAF sensor? Please help with any tips for diagnosing this problem that you can. Thanks.

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If they did not replace the front valve cover with a new updated one when they did the intake the code will come back.there is a tech service bulletin about this . your mass air flow sensor can be cleaned but would recommend a shop do this.

Posted on Feb 01, 2009

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1 Answer

Po171 po174 code


Lean bank 1 and bank 2 , and throttle actuator system fault. Check reason for lean codes 1st, vacuum leak(s), air inlet boot and hoses, or low fuel pressure / clogged filter. Repair as needed then clear codes and recheck .

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Look for vacuum leaks,that are causing the O2 Sensors to go lean, and set codes on both banks

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1995 Windstar OBD II showing codes PO340, PO171, and PO174


Hello;
With those codes, the first place I would check is the fuel pressure. Also check the fuel filter and replace it if you haven't already. Then clear codes and recheck. Even if your fuel pressure is with in range it still may not push enough fuel to operate your vehicle.

Jan 15, 2009 | 1995 Ford Windstar

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