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Old 05-28-2015, 08:44 AM
robert.wynkoop@gmail.com robert.wynkoop@gmail.com is offline
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Default 1996 4.0L OHV High LT Fuel Trims P0171

Working on my sons 1996 Ford Ranger 4.0L with long term fuel trims that are HIGH, due to a lean condition. I have the Autoenginuity with the Ford pack.

I have looked at MASS AF values. Idle: .78, WOT 3.98V.
Upstream OS2 look good and respond to lean / rich. (Lean tested with leak, Rich tested with WOT to IDLE response.)
Fuel Pressure: 28psi at idle running. 35 with fuel regulator vacuum removed.
No upper intake or vacuum leaks that I can find. Canister purge, closed at idle - (Would cause rich, but I'm not sure if my vap line is good, as I have a line running to the back that is full of rust holes.)

I think I need to:
- Block fuel regulator return and verify max fuel pressure. I do not think this is an issue, because I can get 45 pis with truck off and FP jumpered. (I resisting throwing a FP regulator on it, since I'm using a Autozone gauge.)
-Remove PVC from Valve cover. Then block both the PVC hole and crankcase vent input hose near MASS AF and check if I develop a vacuum. I do not this it should, is this correct. If I develop vacuum, I have a lower intake leaking.

Only code is P0171, Lean bank 1(If I recall correctly.) But both banks are adding extra fuel, not just bank 1. Bank 1 is running 18%, bank 2 is running 12%. LTFT do go down a bit off idle, but not to zero, and still more than 5%. I can clear the code, and light has stayed off after a 50 mile highway trip.

This code set in the middle of February, my son says truck sounded like it was out of gas on a cold start.

I think this is going to be a Lower Intake leaking.

Any suggestions on how to confirm, or have I done enough to confirm it.

Robert Wynkoop,
Former ASE tech(1989)
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