Question about 2002 Ford F150 Regular Cab

2 Answers

OBD11 codes Ok have the 171/174 code showing lean problem I have changed Mass ariflow/EGR valve/EGR flow senor and can clear codes and as long as I dont turn the engine off i can drive anywhere and let it idle forever BUT once I shut engine off the next time I drive it and go one mile the codes reappear // Now why would these lean codes not show if I was driving it around for hours and idling for hours ?

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  • Dale Clark Nov 20, 2008

    LOL I like the idea to just burn it and collect insurance but think be more fun if was inside the Ford garage at the time LOL // Truck runs great idles fine gets good gas mileage just driving me nuts LOL

  • bonlucas12 Nov 26, 2008

    I have the same problem. I've changed the o2 sensors, fuel filter, plugs, wires, and the IAC. And cleaned the MAF. Sprayed around all vacume lines and Intake. No change in Idle when spraying carb cleaner, Im at a loss. The truck runs fine but these codes always come back.PLEASE HELP. Runnin outta cash. Thanks,

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Lean codes are codes created when the air/fuel mixture is too much air not enought fuel. With that being said you lean codes are caused be either unmetered air entering the intake such as oiled down intake gaskets or a too little fuel like a weak fuel pump. If the vehicle runs fine I would suspect it to be an air issue. Short of hooking a computer and monitoring the o2 pid data which most causual mechanics wont have you can take a look at all the vacuum lines. A cracked vacuum line will create these lean codes due to air entering after the MAF sensor. A quick an easy trick for finding vacuum leak which is what you will be looking for is brake cleaner. Spray the brake cleaner around the engine taking a spray then stop then listen approach. You will be looking for a rise in engine rpm. A large vacuum leak will also make a hiss noise at idle. Your second question being why will this light only come on after the second key cycle is due to obd2. The system strategy will illuminate a light only when the faults are detected after two drive cycles. The problem is there the first time but the car will illuminate the light until is see the fault the second time. What engine do you have? The 4.2L engine has constant problems with the upper intake gaskets. hope this helps.

Posted on Mar 03, 2009

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Does vehicle run ok ??,if so leave well alone and do not disturb a bag of worms, emmisionwiz might be able to answer this one better but personally i think the problem is more likely to be the software being used? as the newer the vehicle depending on model and make the more likely you are to come up against encrypted software that means its a dealer only solution.Sorry if iam not of any help but iam getting this more and more with cars over the last year or so ,and as for RENAULT ??burn it and claim insurance money

Posted on Nov 20, 2008

  • Colin Stickland
    Colin Stickland Nov 20, 2008

    it was only burn the renault ,not the ford.when i started a tune up kit consisted ot a points file,timing,dwell meter and a nive long thin screwdriver to adjust carb,with a collection of different sized hammers to fix everything else.now every main dealer has bill gates look alike nerdy type to play with the computer and ex lehmans bros bank employee to write the bill out.and with the newer cars in last year i cant evan change the oil without the immobiliser cutting in.think i will have to change my work to say an old ladies companion who husband owned a motor dealers ,snuffed it and left her all the money and income .Because in all honesty here in europe thats how its become now with all this encrypted software being used and iam afraid it will get worse with the introduction of modules,which are like a remote relay box operated by computer signals so say changing a speaker will cause the module to send a signal to computer which cuts the immobiliser in so its dealer only evan to change a speaker or window winder motor ,and it will not release either unless you enter the bar code of the part which you can only get at the dealers.its here already in spain can only work on older cars

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1 Answer

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1 Answer

P0171


There are a number of things that can cause these codes to come up (they mean bank 1 and bank 2 lean fuel mix, which is too much air, or not enough gas ), Here are some possibilities:
common on fords--bad differential pressure sensor (DPFE), this sensor is located on the engine near the EGR valve, it monitors EGR flow, it may be misreading the flow, which increases EGR resulting in a too lean fuel mix. To fix, replace DPFE.
Leak @ PCV valve
Leak @ EGR valve
Dirty Mass Air Flow Sensor
Dirty fuel injectors
Low fuel pressure
Vac leak @ intake manifold.
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