4.2 electrical problem

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Apr 6, 2009 | 05:02 PM

nomore

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Joined: Apr 2009

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4.2 electrical problem

hi everyone, i hope you can help me with my problem. i have a 99 f150 with a 4.2 5 speed. i have the 171 and174 codes and i have read so much about this problem and i'm still lost. i know that these are lean codes left and right and the main source of the problem is a vacuum leak. i have vacuum tested every line under the hood. when i put the motor in new fel-pro intake gaskets went in. the fuel regulator and egr valve held vacuum. i went through 2 cans of starting fluid checking for any leaks. changed the pvc and fuel filter. i am 99 percent sure it's not a vacuum leak. what i have questions about is when i hook up the obd ll reader and i'm watching the readings in the live mode. the iat reading will jump from what the temp is out side to 200 - 300 degrees. when driving the truck the tack will jump 3000 - 5000 rpm with no change in engine speed. this truck runs good and idles @800 rpm and vacuum holds steady at 18 at idle i need help just short of having a marshmellow roast. thanks

Last edited by nomore; Apr 6, 2009 at 05:10 PM. Reason: forgot something

Apr 7, 2009 | 08:36 AM

KingRanchMan02

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Joined: Oct 2005

Posts: 2,209

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From: Louisville, Kentucky

Having the codes for both banks indicates something in common to the two. Something in the air filter and air intake to the throttle body. The IAT sensor is in this tract and is suspect with the live readings. Good luck!